Contents
Cisco Response
Device-Specific Mitigation and Identification
Additional Information
Cisco Security Procedures
Related Information
Alert History
Cisco Response
This Applied Mitigation Bulletin is a companion document to the following
PSIRT Security Advisories:
- Advisory ID: cisco-sa-20120926-sip
- Advisory ID: cisco-sa-20120926-cucm
This document provides identification and mitigation techniques that
administrators can deploy on Cisco network devices.
Vulnerability Characteristics
There is a vulnerability in Cisco products that process
the Session Initiation Protocol (SIP). The following subsections summarize
the vulnerability:
Vulnerability in the Cisco
Unified Communications Manager Session Initiation Protocol (SIP)
implementation: This
vulnerability can be exploited remotely without authentication and without
end-user interaction. Successful exploitation of this vulnerability could cause
a denial of service (DoS) condition. Repeated attempts to exploit this
vulnerability could result in a sustained DoS
- SIP using TCP port 5060
- SIP Transport Layer Security (TLS) using TCP port 5061
- SIP using UDP port 5060
An attacker could exploit the vulnerability using spoofed packets.
Vulnerability in the Session Initiation Protocol (SIP)
implementation in Cisco IOS Software and Cisco IOS XE Software: This
vulnerability can be exploited remotely without authentication and without
end-user interaction. Successful exploitation of this vulnerability could cause
a DoS condition.
Repeated attempts to exploit this vulnerability could result in a sustained DoS condition. The attack vectors for exploitation
are through IPv4 and IPv6 packets using the following protocols and ports:
- SIP using TCP port 5060
- SIP TLS using TCP port 5061
- SIP using UDP port 5060
An attacker could exploit the vulnerability using spoofed packets.
The vulnerability in the two advisories has been assigned Common Vulnerabilities and Exposures
(CVE) identifier CVE-2012-3949.
Information about vulnerable, unaffected, and fixed software is available in
the Cisco Security Advisories, which are available at the following links:
http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20120926-sip
http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20120926-cucm
Mitigation Technique Overview
Cisco devices provide several countermeasures for this vulnerability.
Administrators are advised to consider these protection methods to be general
security best practices for infrastructure devices and the traffic that
transits the network. This section of the document provides an overview of
these techniques.
Cisco IOS Software can provide effective means of exploit prevention using
the following methods:
- Infrastructure access control lists (iACLs)
- Transit access control lists (tACLs)
- Unicast Reverse Path Forwarding (uRPF)
- IP source guard (IPSG)
These protection mechanisms filter and drop, as well as verify the source IP
address of, packets that are attempting to exploit this vulnerability.
The proper deployment and configuration of uRPF provides an effective means
of protection against attacks that use packets with spoofed source IP
addresses. uRPF should be deployed as close to all traffic sources as
possible.
The proper deployment and configuration of IPSG provides an effective means
of protection against spoofing attacks at the access layer.
Effective means of exploit prevention can also be provided by the Cisco ASA
5500 Series Adaptive Security Appliance, Cisco Catalyst 6500 Series ASA
Services Module (ASASM), and the Firewall Services Module (FWSM) for Cisco
Catalyst 6500 Series Switches and Cisco 7600 Series Routers using the
following:
These protection mechanisms filter and drop, as well as verify the source IP
address of, packets that are attempting to exploit this vulnerability.
Cisco IOS NetFlow records can provide visibility into network-based
exploitation attempts.
Cisco IOS Software, Cisco ASA, Cisco ASASM, and Cisco FWSM firewalls can
provide visibility through syslog messages and counter values displayed in the
output from show commands.
Effective use of Cisco Intrusion Prevention System (IPS) event actions
provides visibility into and protection against attacks that attempt to exploit
this vulnerability.
The Cisco Security Manager can also provide visibility through incidents,
queries, and event reporting.
Risk Management
Organizations are advised to follow their standard risk evaluation and
mitigation processes to determine the potential impact of this
vulnerability. Triage refers to sorting projects and prioritizing efforts
that are most likely to be successful. Cisco has provided documents that can
help organizations develop a risk-based triage capability for their information
security teams. Risk
Triage for Security Vulnerability Announcements and Risk
Triage and Prototyping can help organizations develop repeatable security
evaluation and response processes.
Device-Specific Mitigation and Identification
Caution: The effectiveness of any
mitigation technique depends on specific customer situations such as product
mix, network topology, traffic behavior, and organizational mission. As with
any configuration change, evaluate the impact of this configuration prior to
applying the change.
Specific information about mitigation and identification is available for
these devices:
Mitigation: Infrastructure Access Control Lists
To protect infrastructure devices and minimize the risk, impact, and effectiveness of direct infrastructure attacks, administrators are advised to deploy infrastructure access control lists (iACLs) to perform policy enforcement of traffic sent to infrastructure equipment. Administrators can construct an iACL by explicitly permitting only authorized traffic sent to infrastructure devices in accordance with existing security policies and configurations. For the maximum protection of infrastructure devices, deployed iACLs should be applied in the ingress direction on all interfaces to which an IP address has been configured. An iACL workaround cannot provide complete protection against this vulnerability when the attack originates from a trusted source address.
The iACL policy denies unauthorized SIP packets on TCP and UDP ports 5060 and SIP-TLS on TCP port 5061 that are sent to affected devices. In the following example, 192.168.60.0/24 and 2001:DB8:1:60::/64 represent the IP address space that is used by the affected devices, and the hosts at 192.168.100.1 and 2001:DB8:1:100::1 are considered trusted sources that require access to the affected devices. Care should be taken to allow required traffic for routing and administrative access prior to denying all unauthorized traffic. Whenever possible, infrastructure address space should be distinct from the address space used for user and services segments. Using this addressing methodology will assist with the construction and deployment of iACLs.
Additional information about iACLs is in Protecting Your Core: Infrastructure Protection Access Control Lists.
ip access-list extended Infrastructure-ACL-Policy
!
!-- Include explicit permit statements for trusted sources
!-- that require access on the vulnerable TCP and UDP ports
!
permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5060
permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5061
permit udp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5060
!
!-- The following vulnerability-specific access control entries
!-- (ACEs) can aid in identification of attacks
!
deny tcp any 192.168.60.0 0.0.0.255 eq 5060
deny tcp any 192.168.60.0 0.0.0.255 eq 5061
deny udp any 192.168.60.0 0.0.0.255 eq 5060
!
!-- Explicit deny ACE for traffic sent to addresses configured within
!-- the infrastructure address space
!
deny ip any 192.168.60.0 0.0.0.255
!
!-- Permit or deny all other Layer 3 and Layer 4 traffic in accordance
!-- with existing security policies and configurations
!
!
!-- Create the corresponding IPv6 tACL
!
ipv6 access-list IPv6-Infrastructure-ACL-Policy
!
!-- Include explicit permit statements for trusted sources
!-- that require access on the vulnerable protocols and ports
!
permit tcp host 2001:DB8:1:100::1 2001:DB8:1:60::/64 eq 5060
permit tcp host 2001:DB8:1:100::1 2001:DB8:1:60::/64 eq 5061
permit udp host 2001:DB8:1:100::1 2001:DB8:1:60::/64 eq 5060
!
!-- The following vulnerability-specific access control entries
!-- (ACEs) can aid in identification of attacks to global and
!-- link local addresses
!
deny tcp any 2001:DB8:1:60::/64 eq 5060
deny tcp any 2001:DB8:1:60::/64 eq 5061
deny udp any 2001:DB8:1:60::/64 eq 5060
!
!-- Permit other required traffic to the infrastructure address
!-- range and allow IPv6 Neighbor Discovery packets, which
!-- include Neighbor Solicitation packets and Neighbor
!-- Advertisement packets
!
permit icmp any any nd-ns
permit icmp any any nd-na
!
!-- Explicit deny for all other IPv6 traffic to the global
!-- infrastructure address range
!
deny ipv6 any 2001:DB8:1:60::/64
!
!-- Permit or deny all other Layer 3 and Layer 4 traffic
!-- in accordance with existing security policies and configurations
!
!
!-- Apply tACLs to interfaces in the ingress direction
!
interface GigabitEthernet0/0
ip access-group Infrastructure-ACL-Policy in
ipv6 traffic-filter IPv6-Infrastructure-ACL-Policy in
Note that filtering with an interface access list will elicit the transmission of ICMP unreachable messages back to the source of the filtered traffic. Generating these messages could have the undesired effect of increasing CPU utilization on the device. In Cisco IOS Software, ICMP unreachable generation is limited to one packet every 500 milliseconds by default. ICMP unreachable message generation can be disabled using the interface configuration command no ip unreachables. ICMP unreachable rate limiting can be changed from the default using the global configuration command ip icmp rate-limit unreachable interval-in-ms.
Identification: Infrastructure Access Control Lists
After the administrator applies the iACL to an interface, the show ip access-lists and show ipv6 access-list
commands will identify the number of SIP packets on TCP and UDP port
5060 and SIP-TLS on TCP and UDP port 5061 that have been filtered on
interfaces on which the iACL is applied. Administrators should
investigate filtered packets to determine whether they are attempts to
exploit this vulnerability. Example output for show ip access-lists Infrastructure-ACL-Policy follows:
router#show ip access-lists Infrastructure-ACL-Policy
Extended IP access list Infrastructure-ACL-Policy
10 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5060 (60 matches)
20 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5061 (41 matches)
30 permit udp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5060 (188 matches)
40 deny tcp any 192.168.60.0 0.0.0.255 eq 5060 (9 matches)
50 deny tcp any 192.168.60.0 0.0.0.255 eq 5061 (18 matches)
60 deny udp any 192.168.60.0 0.0.0.255 eq 5060 (34 matches)
70 deny ip any 192.168.60.0 0.0.0.255 (17 matches)
router#
In the preceding example, access list Infrastructure-ACL-Policy has dropped the following packets that are received from an untrusted host or network:
- 9 SIP packets on TCP port 5060 for ACE line 40
- 18 SIP packets on TCP port 5061 for ACE line 50
- 34 SIP packets on UDP port 5060 for ACE line 60
router#show ipv6 access-list IPv6-Infrastructure-ACL-Policy
IPv6 access list IPv6-Infrastructure-ACL-Policy
permit tcp host 2001:DB8:1:100::1 2001:DB8:1:60::/64 eq 5060
(71 matches) sequence 10
permit tcp host 2001:DB8:1:100::1 2001:DB8:1:60::/64 eq 5061
(85 matches) sequence 20
permit udp host 2001:DB8:1:100::1 2001:DB8:1:60::/64 eq 5060
(512 matches) sequence 30
deny tcp any 2001:DB8:1:60::/64 eq 5060 (58 matches) sequence 40
deny tcp any 2001:DB8:1:60::/64 eq 5061 (81 matches) sequence 50
deny udp any 2001:DB8:1:60::/64 eq 5060 (216 matches) sequence 60
permit icmp any any nd-ns (80 matches) sequence 70
permit icmp any any nd-na (80 matches) sequence 80
deny ipv6 any 2001:DB8:1:60::/64 (5 matches) sequence 90
In the preceding example, access list IPv6-Infrastructure-ACL-Policy has dropped the following
- 58 SIP packets on TCP port 5060 for ACE line 40
- 81 SIP packets on TCP port 5061 for ACE line 50
- 216 SIP packets on UDP port 5060 for ACE line 60
For additional information about investigating incidents using ACE counters and syslog events, reference the Identifying Incidents Using Firewall and IOS Router Syslog Events Applied Intelligence white paper.
Administrators can use Embedded Event Manager to provide
instrumentation when specific conditions are met, such as ACE counter
hits. The Applied Intelligence white paper Embedded Event Manager in a Security Context provides additional details about how to use this feature.
Mitigation: Transit Access Control Lists
To protect the network from traffic that enters the network at ingress
access points, which may include Internet connection points, partner and
supplier connection points, or VPN connection points, administrators are
advised to deploy transit access control lists (tACLs) to perform policy
enforcement. Administrators can construct a tACL by explicitly permitting only
authorized traffic to enter the network at ingress access points or permitting
authorized traffic to transit the network in accordance with existing security
policies and configurations. A tACL workaround cannot provide complete
protection against this vulnerability when the attack originates from a
trusted source address.
The tACL policy denies unauthorized SIP IPv4 and IPv6 packets on TCP ports
5060 and 5061 and UDP port 5060 that are sent to affected devices. In
the following example, 192.168.60.0/24 and 2001:DB8:1:60::/64 represent the IP
address space that is used by the affected devices, and the hosts at
192.168.100.1 and 2001:DB8::100:1 are considered trusted sources that require
access to the affected devices. Care should be taken to allow required traffic
for routing and administrative access prior to denying all unauthorized
traffic.
Additional information about tACLs is in Transit
Access Control Lists: Filtering at Your Edge.
!
!-- Include explicit permit statements for trusted sources
!-- that require access on the vulnerable TCP and UDP ports
!
access-list 150 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5060
access-list 150 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5061
access-list 150 permit udp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5060
!
!-- The following vulnerability-specific access control entries
!-- (ACEs) can aid in identification of attacks
!
access-list 150 deny tcp any 192.168.60.0 0.0.0.255 eq 5060
access-list 150 deny tcp any 192.168.60.0 0.0.0.255 eq 5061
access-list 150 deny udp any 192.168.60.0 0.0.0.255 eq 5060
!
!-- Permit or deny all other Layer 3 and Layer 4 traffic in accordance
!-- with existing security policies and configurations
!
!-- Explicit deny for all other IP traffic
!
access-list 150 deny ip any any
!
!-- Create the corresponding IPv6 tACL
!
ipv6 access-list IPv6-Transit-ACL-Policy
!
!-- Include explicit permit statements for trusted sources
!-- that require access on the vulnerable TCP and UDP ports
!
permit tcp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 5060
permit tcp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 5061
permit udp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 5060
!
!-- The following vulnerability-specific ACEs can
!-- aid in identification of attacks to global and
!-- link-local addresses
!
deny tcp any 2001:DB8:1:60::/64 eq 5060
deny tcp any 2001:DB8:1:60::/64 eq 5061
deny udp any 2001:DB8:1:60::/64 eq 5060
!
!-- Permit or deny all other Layer 3 and Layer 4 traffic in
!-- accordance with existing security policies and configurations
!-- and allow IPv6 neighbor discovery packets, which
!-- include neighbor solicitation packets and neighbor
!-- advertisement packets
!
permit icmp any any nd-ns
permit icmp any any nd-na
!
!-- Explicit deny for all other IPv6 traffic
!
deny ipv6 any any
!
!
!-- Apply tACLs to interfaces in the ingress direction
!
interface GigabitEthernet0/0
ip access-group 150 in
ipv6 traffic-filter IPv6-Transit-ACL-Policy in
Note that filtering with an interface access list will elicit the
transmission of ICMP unreachable messages back to the source of the filtered
traffic. Generating these messages could have the undesired effect of
increasing CPU utilization on the device. In Cisco IOS Software, ICMP
unreachable generation is limited to one packet every 500 milliseconds by
default. ICMP unreachable message generation can be disabled using the
interface configuration commands no ip unreachables and
no ipv6 unreachables. ICMP unreachable rate limiting can be
changed from the default using the global configuration commands ip
icmp rate-limit unreachable interval-in-ms and ipv6
icmp error-interval interval-in-ms.
Identification: Transit Access Control Lists
After the administrator applies the tACL to an interface, the show
ip access-lists and show ipv6 access-list commands
will identify the number of SIP IPv4 and IPv6 packets on TCP ports 5060 and
5061 and UDP port 5060 that have been filtered. Administrators are
advised to investigate filtered packets to determine whether they are attempts
to exploit this vulnerability. Example output for show ip
access-lists 150 and show ipv6 access-list
IPv6-Transit-ACL-Policy follows:
router#show ip access-lists 150
Extended IP access list 150
10 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5060
20 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5061
30 permit udp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5060
40 deny tcp any 192.168.60.0 0.0.0.255 eq 5060 (57 matches)
50 deny tcp any 192.168.60.0 0.0.0.255 eq 5061 (40 matches)
60 deny udp any 192.168.60.0 0.0.0.255 eq 5060 (18 matches)
70 deny ip any any
router#
In the preceding example, access list 150 has dropped the following packets
received from an untrusted host or network:
- 57 SIP packets on TCP port 5060 for ACE
line 40
- 40 SIP packets on TCP port 5061 for ACE
line 50
- 18 SIP packets on UDP port 5060 for ACE
line 60
router#show ipv6 access-list IPv6-Transit-ACL-Policy
IPv6 access list IPv6-Transit-ACL-Policy
permit tcp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 5060 (55 matches) sequence 10
permit tcp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 5061 (38 matches) sequence 20
permit udp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 5060 (210 matches) sequence 30
deny tcp any 2001:DB8:1:60::/64 eq 5060 (18 matches) sequence 40
deny tcp any 2001:DB8:1:60::/64 eq 5061 (21 matches) sequence 50
deny udp any 2001:DB8:1:60::/64 eq 5060 (87 matches) sequence 60
permit icmp any any nd-ns (41 matches) sequence 70
permit icmp any any nd-na (41 matches) sequence 80
deny ipv6 any any (21 matches) sequence 90
In the preceding example, access list IPv6-Transit-ACL-Policy has
dropped the following packets received from an untrusted host or network:
- 18 SIP packets on TCP port 5060 for ACE
line 40
- 21 SIP packets on TCP port 5061 for ACE
line 50
- 87 SIP packets on UDP port 5060 for ACE
line 60
For additional information about investigating incidents using ACE counters
and syslog events, reference the Identifying
Incidents Using Firewall and IOS Router Syslog Events Cisco Security
Intelligence Operations white paper.
Administrators can use Embedded Event Manager to provide instrumentation
when specific conditions are met, such as ACE counter hits. The Cisco Security
Intelligence Operations white paper Embedded
Event Manager in a Security Context provides additional details about how
to use this feature.
Identification: Access List Logging
The log and log-input access control list
(ACL) option will cause packets that match specific ACEs to be logged. The
log-input option enables logging of the ingress interface in
addition to the packet source and destination IP addresses and ports.
Caution: Access control list logging can be very CPU
intensive and must be used with extreme caution. Factors that drive the CPU
impact of ACL logging are log generation, log transmission, and process
switching to forward packets that match log-enabled ACEs.
For Cisco IOS Software, the ip access-list logging interval
interval-in-ms command can limit the effects of process switching
induced by IPv4 ACL logging. The logging rate-limit
rate-per-second [except loglevel] command
limits the impact of log generation and transmission.
The CPU impact from ACL logging can be addressed in hardware on the Cisco
Catalyst 6500 Series Switches and Cisco 7600 Series Routers with Supervisor
Engine 720 or Supervisor Engine 32 using optimized ACL logging.
For additional information about the configuration and use of ACL logging,
reference the Understanding
Access Control List Logging Cisco Security Intelligence Operations white
paper.
Mitigation: Spoofing Protection
Unicast Reverse Path Forwarding
The vulnerability that is described in this document can be exploited by
spoofed IP packets. Administrators can deploy and configure Unicast Reverse
Path Forwarding (uRPF) as a protection mechanism against spoofing.
uRPF is configured at the interface level and can detect and drop packets
that lack a verifiable source IP address. Administrators should not rely on
uRPF to provide complete spoofing protection because spoofed packets may enter
the network through a uRPF-enabled interface if an appropriate return route to
the source IP address exists. Administrators are advised to take care to ensure
that the appropriate uRPF mode (loose or strict) is configured during the
deployment of this feature because it can drop legitimate traffic that is
transiting the network. In an enterprise environment, uRPF may be enabled at
the Internet edge and the internal access layer on the user-supporting Layer 3
interfaces.
Identification: Spoofing Protection Using Unicast Reverse Path
Forwarding
With uRPF properly deployed and configured throughout the network
infrastructure, administrators can use the show cef interface
type slot/port internal, show ip
interface, show cef drop, show ip cef
switching statistics feature, and show ip traffic
commands to identify the number of packets that uRPF has dropped.
Note: Beginning with Cisco IOS Software Release 12.4(20)T,
the command show ip cef switching has been replaced by
show ip cef switching statistics feature.
Note: The show command |
begin regex and show command
| include regex command modifiers are used in the
following examples to minimize the amount of output that administrators will
need to parse to view the desired information. Additional information about
command modifiers is in the show
command sections of the Cisco IOS Configuration Fundamentals Command
Reference.
router#show cef interface GigabitEthernet 0/0 internal | include drop
ip verify: via=rx (allow default), acl=0, drop=18, sdrop=0
router#
Note: show cef interface type
slot/port internal is a hidden command that must be fully
entered at the command-line interface. Command completion is not available for
it.
router#show ip interface GigabitEthernet 0/0 | begin verify
IP verify source reachable-via RX, allow default, allow self-ping
18 verification drops
0 suppressed verification drops
router#
router#show cef drop
CEF Drop Statistics
Slot Encap_fail Unresolved Unsupported No_route No_adj ChkSum_Err
RP 27 0 0 18 0 0
router#
router#show ip cef switching statistics feature
IPv4 CEF input features:
Path Feature Drop Consume Punt Punt2Host Gave route
RP PAS uRPF 18 0 0 0 0
Total 18 0 0 0 0
-- CLI Output Truncated --
router#
router#show ip traffic | include RPF
18 no route, 18 unicast RPF, 0 forced drop
router#
In the preceding show cef interface GigabitEthernet 0/0 internal, show ip interface GigabitEthernet 0/0, show cef drop, show ip cef
switching statistics feature, and show ip traffic
examples, uRPF has dropped 18 IP packets received globally on
all interfaces with uRPF configured because of the inability to verify the
source address of the IP packets within the forwarding information base of
Cisco Express Forwarding.
Additional information is in the Unicast
Reverse Path Forwarding Loose Mode Feature Guide.
For additional information about the configuration and use of uRPF,
reference the Understanding
Unicast Reverse Path Forwarding Cisco Security Intelligence Operations
white paper.
IP Source Guard
IP source guard (IPSG) is a security feature that restricts IP traffic on
nonrouted, Layer 2 interfaces by filtering packets based on the DHCP snooping
binding database and manually configured IP source bindings. Administrators can
use IPSG to prevent attacks from an attacker who attempts to spoof packets by
forging the source IP address and/or the MAC address. When properly deployed
and configured, IPSG coupled with strict mode uRPF provides the most effective
means of spoofing protection for the vulnerability that is described in this
document.
Additional information about the deployment and configuration of IPSG is in
Configuring
DHCP Features and IP Source Guard.
Identification: IPv4 Traffic Flow Identification Using Cisco IOS
NetFlow
Administrators can configure Cisco IOS NetFlow on Cisco IOS routers and
switches to aid in the identification of IPv4 traffic flows that may be
attempts to exploit this vulnerability. Administrators are advised to
investigate flows to determine whether they are attempts to exploit this
vulnerability or whether they are legitimate traffic flows.
router#show ip cache flow
IP packet size distribution (90784136 total packets):
1-32 64 96 128 160 192 224 256 288 320 352 384 416 448 480
.000 .698 .011 .001 .004 .005 .000 .004 .000 .000 .003 .000 .000 .000 .000
512 544 576 1024 1536 2048 2560 3072 3584 4096 4608
.000 .001 .256 .000 .010 .000 .000 .000 .000 .000 .000
IP Flow Switching Cache, 4456704 bytes
1885 active, 63651 inactive, 59960004 added
129803821 ager polls, 0 flow alloc failures
Active flows timeout in 30 minutes
Inactive flows timeout in 15 seconds
IP Sub Flow Cache, 402056 bytes
0 active, 16384 inactive, 0 added, 0 added to flow
0 alloc failures, 0 force free
1 chunk, 1 chunk added
last clearing of statistics never
Protocol Total Flows Packets Bytes Packets Active(Sec) Idle(Sec)
-------- Flows /Sec /Flow /Pkt /Sec /Flow /Flow
TCP-Telnet 11393421 2.8 1 48 3.1 0.0 1.4
TCP-FTP 236 0.0 12 66 0.0 1.8 4.8
TCP-FTPD 21 0.0 13726 1294 0.0 18.4 4.1
TCP-WWW 22282 0.0 21 1020 0.1 4.1 7.3
TCP-X 719 0.0 1 40 0.0 0.0 1.3
TCP-BGP 1 0.0 1 40 0.0 0.0 15.0
TCP-Frag 70399 0.0 1 688 0.0 0.0 22.7
TCP-other 47861004 11.8 1 211 18.9 0.0 1.3
UDP-DNS 582 0.0 4 73 0.0 3.4 15.4
UDP-NTP 287252 0.0 1 76 0.0 0.0 15.5
UDP-other 310347 0.0 2 230 0.1 0.6 15.9
ICMP 11674 0.0 3 61 0.0 19.8 15.5
IPv6INIP 15 0.0 1 1132 0.0 0.0 15.4
GRE 4 0.0 1 48 0.0 0.0 15.3
Total: 59957957 14.8 1 196 22.5 0.0 1.5
SrcIf SrcIPaddress DstIf DstIPaddress Pr SrcP DstP Pkts
Gi0/0 192.168.10.201 Gi0/1 192.168.60.102 11 0984 13C4 1
Gi0/0 192.168.11.54 Gi0/1 192.168.60.158 06 0911 13C5 3
Gi0/1 192.168.150.60 Gi0/0 10.89.16.226 06 0016 12CA 1
Gi0/0 192.168.13.97 Gi0/1 192.168.60.28 06 0B3E 13C4 5
Gi0/0 192.168.10.17 Gi0/1 192.168.60.97 11 0B89 13C5 1
Gi0/0 10.88.226.1 Gi0/1 192.168.202.22 11 007B 007B 1
Gi0/0 192.168.12.185 Gi0/1 192.168.60.239 11 0BD7 13C4 1
Gi0/0 10.89.16.226 Gi0/1 192.168.150.60 06 12CA 0016 1
router#
In the preceding example, there are multiple flows for SIP
on TCP ports 5060 (hex value 13C4) and
5061 (hex value 13C5) and UDP port
5060 (hex value 13C4).
This traffic is sourced from and sent to addresses within the
192.168.60.0/24 address block, which is used by affected devices. The packets
in these flows may be spoofed and may indicate an attempt to exploit this
vulnerability. Administrators are advised to compare these flows to baseline
utilization for SIP traffic sent on UDP port 5060 and also
investigate the flows to determine whether they are sourced from untrusted
hosts or networks.
As shown in the following example, to view only the SIP packets on TCP port
5060 (hex value 13C4) and TCP port 5061 (hex value 13C5), use the show
ip cache flow | include SrcIf|_06_.*(13C4|13C5)_ command to display
the related Cisco NetFlow records:
TCP Flows
router#show ip cache flow | include SrcIf|_06_.*(13C4|13C5)_
SrcIf SrcIPaddress DstIf DstIPaddress Pr SrcP DstP Pkts
Gi0/0 192.168.12.110 Gi0/1 192.168.60.163 06 092A 13C5 6
Gi0/0 192.168.11.230 Gi0/1 192.168.60.20 06 0C09 13C4 1
Gi0/0 192.168.11.131 Gi0/1 192.168.60.245 06 0B66 13C4 18
Gi0/0 192.168.13.7 Gi0/1 192.168.60.162 06 0914 13C5 1
Gi0/0 192.168.41.86 Gi0/1 192.168.60.27 06 0B7B 13C5 2
router#
As shown in the following example, to view only the SIP packets on UDP port
5060 (hex value 13C4), use the show
ip cache flow | include SrcIf|_11_.*(13C4)_ command to display
the related Cisco NetFlow records:
UDP Flows
router#show ip cache flow | include SrcIf|_11_.*(13C4)_
SrcIf SrcIPaddress DstIf DstIPaddress Pr SrcP DstP Pkts
Gi0/0 192.168.12.110 Gi0/1 192.168.60.183 11 392A 13C4 6
Gi0/0 192.168.11.230 Gi0/1 192.168.60.220 11 2809 13C4 1
Gi0/0 192.168.13.7 Gi0/1 192.168.60.12 11 1914 13C4 1
Gi0/0 192.168.41.86 Gi0/1 192.168.60.127 11 3B7B 13C4 2
router#
Identification: IPv6 Traffic Flow Identification Using Cisco IOS
NetFlow
Administrators can configure Cisco IOS NetFlow on Cisco IOS routers and
switches to aid in the identification of IPv6 traffic flows that may be
attempts to exploit the vulnerability that is described in this document.
Administrators are advised to investigate flows to determine whether they are
attempts to exploit this vulnerability or whether they are legitimate
traffic flows.
The following output is from a Cisco IOS device running Cisco IOS Software
12.4 mainline train. The command syntax will vary for different Cisco IOS
Software trains.
router#show ipv6 flow cache
IP packet size distribution (50078919 total packets):
1-32 64 96 128 160 192 224 256 288 320 352 384 416 448 480
.000 .990 .001 .008 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000
512 544 576 1024 1536 2048 2560 3072 3584 4096 4608
.000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000
IP Flow Switching Cache, 475168 bytes
8 active, 4088 inactive, 6160 added
1092984 ager polls, 0 flow alloc failures
Active flows timeout in 30 minutes
Inactive flows timeout in 15 seconds
IP Sub Flow Cache, 33928 bytes
16 active, 1008 inactive, 12320 added, 6160 added to flow
0 alloc failures, 0 force free
1 chunk, 1 chunk added
SrcAddress InpIf DstAddress OutIf Prot SrcPrt DstPrt Packets
2001:DB...06::201 Gi0/0 2001:DB...28::20 Local 0x11 0x16C4 0x13C4 1464
2001:DB...6A:5BA6 Gi0/0 2001:DB...28::21 Gi0/1 0x3A 0x0000 0x8000 1191
2001:DB...6A:5BA6 Gi0/0 2001:DB...134::3 Gi0/1 0x3A 0x0000 0x8000 1191
2001:DB...6A:5BA6 Gi0/0 2001:DB...128::4 Gi0/1 0x3A 0x0000 0x8000 1192
2001:DB...6A:5BA6 Gi0/0 2001:DB...128::2 Gi0/1 0x06 0x160A 0x13C4 1597
2001:DB...06::201 Gi0/0 2001:DB...128::3 Gi0/1 0x06 0x1610 0x13C5 1001
2001:DB...06::201 Gi0/0 2001:DB...128::4 Gi0/1 0x11 0x1634 0x13C4 1292
2001:DB...6A:5BA6 Gi0/0 2001:DB...128::3 Gi0/1 0x3A 0x0000 0x8000 1155
2001:DB...6A:5BA6 Gi0/0 2001:DB...146::3 Gi0/1 0x3A 0x0000 0x8000 1092
2001:DB...6A:5BA6 Gi0/0 2001:DB...144::4 Gi0/1 0x3A 0x0000 0x8000 1193
To permit display of the full 128-bit IPv6 address, use the terminal
width 132 exec mode command.
In the preceding example, there are multiple IPv6 flows for
SIP on TCP ports 5060 (hex value
13C4) and 5061 (hex value 13C5) and
UDP port 5060 (hex value 13C4).
The SIP packets on UDP port 5060 are sourced from and sent to
addresses within the 2001:DB8:1:60::/64 address block that is used by affected
devices. The packets in the UDP flows may be spoofed and could indicate an
attempt to exploit this vulnerability. Administrators are advised to compare
these flows to baseline utilization for SIP traffic on UDP port 5060
and also investigate the flows to determine whether they are sourced from
untrusted hosts or networks.
As shown in the following example, to view only the SIP packets on TCP ports
5060 (hex value 13C4) and 5061 (hex value 13C5), use the show ipv6 flow
cache | include SrcIf|_06_.*(13C4|13C5)_ command to display the
related Cisco NetFlow records:
TCP Flows
router#show ipv6 flow cache | include SrcIf|_06_.*(13C4|13C5)_
SrcAddress InpIf DstAddress OutIf Prot SrcPrt DstPrt Packets
2001:DB...6A:5BA6 Gi0/0 2001:DB...128::2 Gi0/1 0x06 0x160A 0x13C5 1597
2001:DB...06::201 Gi0/0 2001:DB...128::3 Gi0/1 0x06 0x1610 0x13C4 1001
router#
As shown in the following example, to view only the SIP packets on UDP ports
5060 (hex value 13C4), use the show ipv6 flow
cache | include SrcIf|_11_.*(13C4)_ command to display the
related Cisco NetFlow records:
UDP Flows
router#show ipv6 flow cache | include SrcIf|_11_.*(13C4)_
SrcAddress InpIf DstAddress OutIf Prot SrcPrt DstPrt Packets
2001:DB...06::201 Gi0/0 2001:DB...28::20 Local 0x11 0x16C4 0x13C4 1464
2001:DB...06::201 Gi0/0 2001:DB...128::3 Gi0/1 0x11 0x1610 0x13C5 1001
2001:DB...06::201 Gi0/0 2001:DB...128::4 Gi0/1 0x11 0x1634 0x13C4 1292
router#
Identification: IPv4 Traffic Flow Identification Using Cisco Flexible
NetFlow
Introduced in Cisco IOS Software Releases 12.2(31)SB2 and 12.4(9)T, Cisco
IOS Flexible NetFlow improves original Cisco NetFlow by adding the capability
to customize the traffic analysis parameters for the administrator''s specific
requirements. Original Cisco NetFlow uses a fixed seven tuples of IP
information to identify a flow, whereas Cisco IOS Flexible NetFlow allows the
flow to be user defined. It facilitates the creation of more complex
configurations for traffic analysis and data export by using reusable
configuration components.
The following example output is from a Cisco IOS device that is running a
version of Cisco IOS Software in the 15.1T train. Although the
syntax will be almost identical for the 12.4T and 15.0 trains, it may vary
slightly depending on the actual Cisco IOS release being used. In the following
configuration, Cisco IOS Flexible NetFlow will collect information on interface
GigabitEthernet0/0 for incoming IPv4 flows based on source IPv4 address, as
defined by the match ipv4 source address key field statement.
Cisco IOS Flexible NetFlow will also include nonkey field information about
source and destination IPv4 addresses, protocol, ports (if present), ingress
and egress interfaces, and packets per flow.
!
!-- Configure key and nonkey fields
!-- in the user-defined flow record
!
flow record FLOW-RECORD-ipv4
match ipv4 source address
collect ipv4 protocol
collect ipv4 destination address
collect transport source-port
collect transport destination-port
collect interface input
collect interface output
collect counter packets
!
!-- Configure the flow monitor to
!-- reference the user-defined flow
!-- record
!
flow monitor FLOW-MONITOR-ipv4
record FLOW-RECORD-ipv4
!
!-- Apply the flow monitor to the interface
!-- in the ingress direction
!
interface GigabitEthernet0/0
ip flow monitor FLOW-MONITOR-ipv4 input
The Cisco IOS Flexible NetFlow flow output is as follows:
router#show flow monitor FLOW-MONITOR-ipv4 cache format table
Cache type: Normal
Cache size: 4096
Current entries: 6
High Watermark: 1
Flows added: 9181
Flows aged: 9175
- Active timeout ( 1800 secs) 9000
- Inactive timeout ( 15 secs) 175
- Event aged 0
- Watermark aged 0
- Emergency aged 0
IPV4 SRC ADDR ipv4 dst addr trns src port trns dst port intf input intf output pkts ip prot
=============== =============== ============= ============= ========== =========== ===== =======
192.168.10.201 192.168.60.102 1456 5060 Gi0/0 Gi0/1 1128 6
192.168.11.54 192.168.60.158 4123 5061 Gi0/0 Gi0/1 2212 17
192.168.150.60 10.89.16.226 2567 443 Gi0/0 Gi0/1 13 6
192.168.13.97 192.168.60.28 3451 5061 Gi0/0 Gi0/1 1 6
192.168.10.17 192.168.60.97 4231 5060 Gi0/0 Gi0/1 146 17
10.88.226.1 192.168.202.22 2678 443 Gi0/0 Gi0/1 10567 6
10.89.16.226 192.168.150.60 3562 80 Gi0/0 Gi0/1 30012 6
To view only SIP on TCP ports
5060 and 5061, use the show flow
monitor FLOW-MONITOR-ipv4 cache format table | include IPV4 DST ADDR
|_6_.*(5060|5061)_ command to display the related NetFlow records.
To view only SIP on UDP ports
5060, use the show flow
monitor FLOW-MONITOR-ipv4 cache format table | include IPV4 DST ADDR
|_17_.*(5060)_ command to display the related NetFlow records.
For more information about Cisco IOS Flexible NetFlow, refer to Flexible
Netflow Configuration Guide, Cisco IOS Release 15.1M&T and Cisco
IOS Flexible NetFlow Configuration Guide, Release 12.4T.
Identification: IPv6 Traffic Flow Identification Using Cisco IOS Flexible
NetFlow
The following example output is from a Cisco IOS device that is running a
version of Cisco IOS Software in the 15.1T train. Although the
syntax will be almost identical for the 12.4T and 15.0 trains, it may vary
slightly depending on the actual Cisco IOS release being used. In the following
configuration, Cisco IOS Flexible NetFlow will collect information on interface
GigabitEthernet0/0 for incoming IPv6 flows based on the source IPv6 address, as
defined by the match ipv6 source address key field statement.
Cisco IOS Flexible NetFlow will also include nonkey field information about
source and destination IPv6 addresses, protocol, ports (if present), ingress
and egress interfaces, and packets per flow.
!
!-- Configure key and nonkey fields
!-- in the user-defined flow record
!
flow record FLOW-RECORD-ipv6
match ipv6 source address
collect ipv6 protocol
collect ipv6 destination address
collect transport source-port
collect transport destination-port
collect interface input
collect interface output
collect counter packets
!
!-- Configure the flow monitor to
!-- reference the user-defined flow
!-- record
!
flow monitor FLOW-MONITOR-ipv6
record FLOW-RECORD-ipv6
!
!-- Apply the flow monitor to the interface
!-- in the ingress direction
!
interface GigabitEthernet0/0
ipv6 flow monitor FLOW-MONITOR-ipv6 input
The Cisco IOS Flexible NetFlow flow output is as follows:
router#show flow monitor FLOW-MONITOR-ipv6 cache format table
Cache type: Normal
Cache size: 4096
Current entries: 6
High Watermark: 2
Flows added: 539
Flows aged: 532
- Active timeout ( 1800 secs) 350
- Inactive timeout ( 15 secs) 182
- Event aged 0
- Watermark aged 0
- Emergency aged 0
IPV6 SRC ADDR ipv6 dst addr trns src port trns dst port intf input intf output pkts ip prot
================== ================ ============= ============= ========== =========== ==== =======
2001:DB...06::201 2001:DB...28::20 123 123 Gi0/0 Gi0/0 17 17
2001:DB...06::201 2001:DB...28::20 1265 5061 Gi0/0 Gi0/0 1237 6
2001:DB...06::201 2001:DB...28::20 1441 5061 Gi0/0 Gi0/0 2346 6
2001:DB...06::201 2001:DB...28::20 1890 5060 Gi0/0 Gi0/0 5009 6
2001:DB...06::201 2001:DB...28::20 2856 5060 Gi0/0 Gi0/0 486 17
2001:DB...06::201 2001:DB...28::20 3012 53 Gi0/0 Gi0/0 1016 17
2001:DB...06::201 2001:DB...28::20 2477 5061 Gi0/0 Gi0/0 1563 17
To permit display of the full 128-bit IPv6 address, use the terminal
width 132 exec mode command.
To view only SIP on TCP ports
5060 and 5061, use the show flow
monitor FLOW-MONITOR-ipv6 cache format table | include IPV6 DST
ADDR|_6_.*(5060|5061)_ command to display the related Cisco IOS
Flexible NetFlow records.
To view only SIP on UDP ports
5060, use the show flow
monitor FLOW-MONITOR-ipv6 cache format table | include IPV6 DST
ADDR|_17_.*(5060)_ command to display the related Cisco IOS
Flexible NetFlow records.
Mitigation: Transit Access Control Lists
To protect the network from traffic that enters the network at ingress
access points, which may include Internet connection points, partner and
supplier connection points, or VPN connection points, administrators are
advised to deploy tACLs to perform policy enforcement. Administrators can
construct a tACL by explicitly permitting only authorized traffic to enter the
network at ingress access points or permitting authorized traffic to transit
the network in accordance with existing security policies and configurations. A
tACL workaround cannot provide complete protection against this
vulnerability when the attack originates from a trusted source address.
The tACL policy denies unauthorized SIP IPv4 and IPv6 packets on TCP ports
5060 and 5061 and UDP port 5060 that are sent to affected devices. In
the following example, 192.168.60.0/24 and 2001:DB8:1:60::/64 represent the IP
address space that is used by the affected devices, and the hosts at
192.168.100.1 and 2001:DB8::100:1 are considered trusted sources that require
access to the affected devices. Care should be taken to allow required traffic
for routing and administrative access prior to denying all unauthorized
traffic.
Additional information about tACLs is in Transit
Access Control Lists: Filtering at Your Edge.
!
!-- Include explicit permit statements for trusted sources
!-- that require access on the vulnerable TCP and UDP ports
!
access-list tACL-Policy extended permit tcp host 192.168.100.1
192.168.60.0 255.255.255.0 eq 5060
access-list tACL-Policy extended permit tcp host 192.168.100.1
192.168.60.0 255.255.255.0 eq 5061
access-list tACL-Policy extended permit udp host 192.168.100.1
192.168.60.0 255.255.255.0 eq 5060
!
!-- The following vulnerability-specific access control entries
!-- (ACEs) can aid in identification of attacks
!
access-list tACL-Policy extended deny tcp any 192.168.60.0 255.255.255.0 eq 5060
access-list tACL-Policy extended deny tcp any 192.168.60.0 255.255.255.0 eq 5061
access-list tACL-Policy extended deny udp any 192.168.60.0 255.255.255.0 eq 5060
!
!-- Permit or deny all other Layer 3 and Layer 4 traffic in accordance
!-- with existing security policies and configurations
!
!-- Explicit deny for all other IP traffic
!
access-list tACL-Policy extended deny ip any any
!
!-- Create the corresponding IPv6 tACL
!
!-- Include explicit permit statements for trusted sources
!-- that require access on the vulnerable TCP and UDP ports
!
ipv6 access-list IPv6-tACL-Policy permit tcp host 2001:DB8::100:1
2001:db8:1:60::/64 eq 5060
ipv6 access-list IPv6-tACL-Policy permit tcp host 2001:DB8::100:1
2001:db8:1:60::/64 eq 5061
ipv6 access-list IPv6-tACL-Policy permit udp host 2001:DB8::100:1
2001:db8:1:60::/64 eq 5060
!
!-- The following vulnerability-specific access control entries
!-- (ACEs) can aid in identification of attacks
!
ipv6 access-list IPv6-tACL-Policy deny tcp any 2001:db8:1:60::/64 eq 5060
ipv6 access-list IPv6-tACL-Policy deny tcp any 2001:db8:1:60::/64 eq 5061
ipv6 access-list IPv6-tACL-Policy deny udp any 2001:db8:1:60::/64 eq 5060
!
!-- Permit or deny all other Layer 3 and Layer 4 traffic in accordance
!-- with existing security policies and configurations
!
!-- Explicit deny for all other IP traffic
!
ipv6 access-list IPv6-tACL-Policy deny ip any any
!
!-- Apply tACLs to interfaces in the ingress direction
!
access-group tACL-Policy in interface outside
access-group IPv6-tACL-Policy in interface outside
Identification: Transit Access Control Lists
After the tACL has been applied to an interface, administrators can use the
show access-list command to identify the number of SIP IPv4
and IPv6 packets on TCP ports 5060 and 5061 and UDP port 5060 that
have been filtered. Administrators are advised to investigate filtered packets
to determine whether they are attempts to exploit this vulnerability.
Example output for show access-list tACL-Policy and
show access-list IPv6-tACL-Policy follows:
firewall#show access-list tACL-Policy
access-list tACL-Policy; 7 elements; name hash: 0x3452703d
access-list tACL-Policy line 1 extended permit tcp host 192.168.100.1
192.168.60.0 255.255.255.0 eq sip (hitcnt=31)
access-list tACL-Policy line 2 extended permit tcp host 192.168.100.1
192.168.60.0 255.255.255.0 eq 5061 (hitcnt=61)
access-list tACL-Policy line 3 extended permit udp host 192.168.100.1
192.168.60.0 255.255.255.0 eq sip (hitcnt=131)
access-list tACL-Policy line 4 extended deny tcp any 192.168.60.0
255.255.255.0 eq sip (hitcnt=8)
access-list tACL-Policy line 5 extended deny tcp any 192.168.60.0
255.255.255.0 eq 5061 (hitcnt=14)
access-list tACL-Policy line 6 extended deny udp any 192.168.60.0
255.255.255.0 eq sip (hitcnt=30)
access-list tACL-Policy line 7 extended deny ip any any (hitcnt=8)
In the preceding example, access list tACL-Policy has dropped the
following packets received from an untrusted host or network:
- 8 SIP packets on TCP port 5060 for ACE
line 4
- 14 SIP packets on TCP port 5061 for ACE
line 5
- 30 SIP packets on UDP port 5060 for ACE
line 6
firewall#show access-list IPv6-tACL-Policy
ipv6 access-list IPv6-tACL-Policy; 7 elements; name hash: 0x566a4229
ipv6 access-list IPv6-tACL-Policy line 1 permit tcp host 2001:db8:1:100::1
2001:db8:1:60::/64 eq sip (hitcnt=59)
ipv6 access-list IPv6-tACL-Policy line 2 permit tcp host 2001:db8:1:100::1
2001:db8:1:60::/64 eq 5061 (hitcnt=28)
ipv6 access-list IPv6-tACL-Policy line 3 permit udp host 2001:db8:1:100::1
2001:db8:1:60::/64 eq sip (hitcnt=124)
ipv6 access-list IPv6-tACL-Policy line 4 deny tcp any
2001:db8:1:60::/64 eq sip (hitcnt=47)
ipv6 access-list IPv6-tACL-Policy line 5 deny tcp any
2001:db8:1:60::/64 eq 5061 (hitcnt=33)
ipv6 access-list IPv6-tACL-Policy line 6 deny udp any
2001:db8:1:60::/64 eq sip (hitcnt=216)
ipv6 access-list IPv6-tACL-Policy line 7 deny ip any any (hitcnt=27)
In the preceding example, access list IPv6-tACL-Policy has dropped
the following packets received from an untrusted host or network:
- 47 SIP packets on TCP port 5060 for ACE
line 4
- 33 SIP packets on TCP port 5061 for ACE
line 5
- 216 SIP packets on UDP port 5060 for
ACE line 6
In addition, syslog message 106023 can provide valuable
information, which includes the source and destination IP address, the source
and destination port numbers, and the IP protocol for the denied packet.
Identification: Firewall Access List Syslog Messages
Firewall syslog message 106023 will be generated for packets denied
by an access control entry (ACE) that does not have the log
keyword present. Additional information about this syslog message is
in Cisco
ASA 5500 Series System Log Message, 8.2 - 106023.
Information about configuring syslog for the Cisco ASA 5500 Series Adaptive
Security Appliance is in Monitoring
- Configuring Logging. Information about configuring syslog on the Cisco
Catalyst 6500 Series ASA Services Module is in Configuring
Logging. Information about configuring syslog on the FWSM for Cisco
Catalyst 6500 Series Switches and Cisco 7600 Series Routers is in Monitoring
the Firewall Services Module.
In the following example, the show logging | grep
regex command extracts syslog messages from the logging buffer on the
firewall. These messages provide additional information about denied packets
that could indicate potential attempts to exploit the vulnerability that is described in this document. It is possible to use different regular expressions
with the grep keyword to search for specific data in the
logged messages.
Additional information about regular expression syntax is in Creating
a Regular Expression.
firewall#show logging | grep 106023
Sep 26 2012 00:15:13: %ASA-4-106023: Deny udp src outside:192.0.2.200/2945
dst inside:192.168.60.33/5060 by access-group "tACL-Policy"
Sep 26 2012 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.88/2949
dst inside:192.168.60.38/5060 by access-group "tACL-Policy"
Sep 26 2012 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.175/2950
dst inside:192.168.60.250/5060 by access-group "tACL-Policy"
Sep 26 2012 00:15:13: %ASA-4-106023: Deny udp src outside:2001:db8:2::2:172/2951
dst inside:2001:db8:1:60::23/5060 by access-group "IPv6-tACL-Policy"
Sep 26 2012 00:15:13: %ASA-4-106023: Deny tcp src outside:2001:db8:d::a85e:172/2952
dst inside:2001:db8:1:60::134/5061 by access-group "IPv6-tACL-Policy"
firewall#
In the preceding example, the messages logged for the tACL
tACL-Policy show potentially spoofed SIP packets for
UDP port 5060 sent to the address
block assigned to affected devices.
Additional information about syslog messages for Cisco ASA Series Adaptive
Security Appliances is in Cisco
ASA 5500 Series System Log Messages, 8.2. Additional information about
syslog messages for Cisco Catalyst 6500 Series ASA Services Module is in the Analyzing
Syslog Messages section of the Cisco
ASASM CLI Configuration Guide. Additional information about syslog messages
for the Cisco FWSM is in Catalyst
6500 Series Switch and Cisco 7600 Series Router Firewall Services Module
Logging System Log Messages.
For additional information about investigating incidents using syslog
events, reference the Identifying
Incidents Using Firewall and IOS Router Syslog Events Cisco Security
Intelligence Operations white paper.
Mitigation: Spoofing Protection Using Unicast Reverse Path Forwarding
The vulnerability that is described in this document can be exploited by
spoofed IP packets. Administrators can deploy and configure uRPF as a
protection mechanism against spoofing.
uRPF is configured at the interface level and can detect and drop packets
that lack a verifiable source IP address. Administrators should not rely on
uRPF to provide complete spoofing protection because spoofed packets may enter
the network through a uRPF-enabled interface if an appropriate return route to
the source IP address exists. In an enterprise environment, uRPF may be enabled
at the Internet edge and at the internal access layer on the user-supporting
Layer 3 interfaces.
For additional information about the configuration and use of uRPF,
reference the Cisco Security Appliance Command Reference for ip
verify reverse-path and the Understanding
Unicast Reverse Path Forwarding Cisco Security Intelligence Operations
white paper.
Identification: Spoofing Protection Using Unicast Reverse Path Forwarding
Firewall syslog message 106021 will be generated for packets denied
by uRPF. Additional information about this syslog message is in Cisco
ASA 5500 Series System Log Message, 8.2 - 106021.
Information about configuring syslog for the Cisco ASA 5500 Series Adaptive
Security Appliance is in Monitoring
- Configuring Logging. Information about configuring syslog for the Cisco
Catalyst 6500 Series ASA Services Module is in Configuring
Logging. Information about configuring syslog on the FWSM for Cisco
Catalyst 6500 Series Switches and Cisco 7600 Series Routers is in Monitoring
the Firewall Services Module.
In the following example, the show logging | grep
regex command extracts syslog messages from the logging buffer on the
firewall. These messages provide additional information about denied packets
that could indicate potential attempts to exploit the vulnerability that is described in this document. It is possible to use different regular expressions
with the grep keyword to search for specific data in the
logged messages.
Additional information about regular expression syntax is in Creating
a Regular Expression.
firewall#show logging | grep 106021
Sep 26 2012 00:15:13: %ASA-1-106021: Deny UDP reverse path check from
192.168.60.1 to 192.168.60.100 on interface outside
Sep 26 2012 00:15:13: %ASA-1-106021: Deny UDP reverse path check from
192.168.60.1 to 192.168.60.100 on interface outside
Sep 26 2012 00:15:13: %ASA-1-106021: Deny TCP reverse path check from
192.168.60.1 to 192.168.60.100 on interface outside
The show asp drop command can also identify the number of
packets that the uRPF feature has dropped, as shown in the following
example:
firewall#show asp drop frame rpf-violated
Reverse-path verify failed 11
firewall#
In the preceding example, uRPF has dropped 11 IP packets
received on interfaces with uRPF configured. Absence of output indicates that
the uRPF feature on the firewall has not dropped packets.
For additional information about debugging accelerated security path dropped
packets or connections, reference the Cisco Security Appliance Command
Reference for show
asp drop.
Identification: Cisco Security Manager
Cisco Security Manager, Event Viewer
Beginning in software version 4.0, Cisco Security Manager can collect
syslogs from Cisco firewalls and Cisco IPS devices and provides the Event
Viewer, which can query for events that are related to the vulnerability that
is described in this document.
Using the following filters in the Firewall Denied Events
predefined view in the Event Viewer provides all captured Cisco firewall access
list deny syslog messages that could indicate potential
attempts to exploit the vulnerability that is described in this document.
- Use the Destination event filter to filter network objects that contain
the IP address space that is used by the affected devices (for example,
IPv4 address range 192.168.60.0/24 and IPv6 address range
2001:DB8:1:60::/64)
- Use the Destination Service event filter to filter objects that contain
TCP ports 5060 and 5061 and UDP port 5060
An Event Type ID filter can be used with the Firewall Denied
Events predefined view in the Event Viewer to filter the syslog IDs
shown in the following list to provide all captured Cisco firewall
deny syslog messages that could indicate potential attempts to
exploit the vulnerability that is described in this document:
- ASA-4-106021 (uRPF spoofing)
- ASA-4-106023 (ACL deny)
For more information about Cisco Security Manager Events, refer to the Filtering
and Querying Events section of the Cisco Security Manager User Guide.
Identification: Event Management System Partner Events
Cisco works with industry-leading Security Information and Event Management
(SIEM) companies through the Cisco
Developer Network. This partnership helps Cisco deliver validated and
pretested SIEM systems that address business concerns such as long-term log
archiving and forensics, heterogeneous event correlation, and advanced
compliance reporting. Security Information and Event Management partner
products can be leveraged to collect events from Cisco devices and then query
the collected events for the incidents created by a
deny syslog messages from firewalls that could indicate
potential attempts to exploit the vulnerability that is described in this
document. The queries can be made by Syslog ID as
shown in the following list:
- ASA-4-106021 (uRPF spoofing)
- ASA-4-106023 (ACL deny)
For more information about SIEM partners, refer to the Security
Management System website.
Additional Information
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Cisco Security Procedures
Complete information on reporting security vulnerabilities in Cisco products, obtaining assistance with security incidents, and registering to receive security information from Cisco, is available on Cisco''s worldwide website at http://www.cisco.com/en/US/products/products_security_vulnerability_policy.html. This includes instructions for press inquiries regarding Cisco security notices. All Cisco security advisories are available at http://www.cisco.com/go/psirt.
Related Information
