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 PSIRT Security Advisory Cisco ASA-CX and Cisco PRSM Log Retention Denial of Service Vulnerability and provides identification and mitigation techniques that
administrators can deploy on Cisco network devices.
Cisco ASA-CX Context-Aware Security appliance and Cisco Prime Security Manager (PRSM) contain a denial of service (DoS) vulnerability in versions prior to 9.0.2-103.
Successful exploitation of this vulnerability on the Cisco ASA-CX could cause the device to stop processing user traffic and prevent management access to the Cisco ASA-CX.
Successful exploitation of this vulnerability on the Cisco PRSM could cause the software to become unresponsive and unavailable.
The vulnerability is documented in Cisco bug ID CSCub70603 (registered customers only) for Cisco ASA-CX Context-Aware Security and Cisco Prime Security Manager and has been assigned Common Vulnerabilities and Exposures (CVE) ID CVE-2012-4629.
Information about vulnerable, unaffected, and fixed software is available in
the Cisco Security Advisory, which is available at the following link: http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20120905-asacx.
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
infrastructure access control lists (iACLs). This protection mechanism
filters and drops packets that are attempting to exploit this
vulnerability.
Effective 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, when an ASA
without the CX services module is protecting an ASA CX with a services module.
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.
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 below denies unauthorized IPv4
and IPv6 packets on TCP ports 22, TCP 443, UDP port 3799, and ICMP echo requests that are sent to affected ASA-CX management interfaces, and additionally TCP Port 446 and UDP port 514 requests that are sent to affected PRSM server management interfaces.
In the following example, 192.168.60.0/24 is the network where the ASA-CX management
interface resides, 192.168.60.6/32 is the PRSM server management interface.
2001:DB8:1:60::/64 represents the IPv6 address space that is used by the
affected ASA-CX management interface and PRSM Server management interface, 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. 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 to the management port on the ASA-CX
!
permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 22
permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 443
permit udp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 3799
permit icmp host 192.168.100.1 192.168.60.0 0.0.0.255 8
!
!-- Include additional permit statements for trusted sources
!-- that require access on the PRSM server
!
permit tcp host 192.168.100.1 host 192.168.60.6 eq 4466
permit udp host 192.168.100.1 host 192.168.60.6 eq 514
!
!-- 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 22
deny tcp any 192.168.60.0 0.0.0.255 eq 443
deny udp any 192.168.60.0 0.0.0.255 eq 3799
deny icmp any 192.168.60.0 0.0.0.255 8
deny tcp any host 192.168.60.6 eq 4466
deny udp any host 192.168.60.6 eq 514
!
!-- 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 protocol and port
!
permit tcp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 22
permit tcp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 443
permit tcp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 4466
permit udp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 3799
permit udp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 514
permit icmp6 host 2001:DB8::100:1 2001:DB8:1:60::/64
!
!-- 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 22
deny tcp any 2001:DB8:1:60::/64 eq 443
deny tcp any 2001:DB8:1:60::/64 eq 4466
deny udp any 2001:DB8:1:60::/64 eq 3799
deny udp any 2001:DB8:1:60::/64 eq 514
!
!-- 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 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: 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 IPv4 and IPv6 packets 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 and show ipv6 access-list IPv6-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 22 (60 matches)
20 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 443 (38 matches)
30 permit udp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 3799 (47 matches)
40 permit icmp host 192.168.100.1 192.168.60.0 0.0.0.255 8 (60 matches)
50 permit tcp host 192.168.100.1 host 192.168.60.6 eq 4466 (45 matches)
60 permit udp host 192.168.100.1 host 192.168.60.6 eq 514 (46 matches)
70 deny tcp any 192.168.60.0 0.0.0.255 eq 22 (9 matches)
80 deny tcp any 192.168.60.0 0.0.0.255 eq 443 (27 matches)
90 deny udp any 192.168.60.0 0.0.0.255 eq 3799(13 matches)
100 deny icmp any 192.168.60.0 0.0.0.255 8 (55 matches)
110 deny tcp any host 192.168.60.6 eq 4466(11 matches)
120 deny udp any host 192.168.60.6 eq 514 (12 matches)
130 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
- 9 SSH packets on TCP port 22 for access control list entry (ACE) line 70.
- 27 HTTPS packets on TCP port 443 for access control list entry (ACE) line 80.
- 13 packets on UDP port 3799 for access control list entry (ACE) line 90.
- 55 ICMP packets for access control list entry (ACE) line 100.
- 11 TCP packets on TCP port 4466 for access control list entry (ACE) line 110.
- 12 SYSLOG packets on UDP port 514 for access control list entry (ACE) line 120.
router#show ipv6 access-list IPv6-Infrastructure-ACL-Policy
IPv6 access list IPv6-Infrastructure-ACL-Policy
permit tcp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 22 (71 matches) sequence 10
permit tcp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 443 (71 matches) sequence 20
permit tcp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 4466 (71 matches) sequence 30
permit udp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 3799 (71 matches) sequence 40
permit udp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 514 (71 matches) sequence 50
permit icmp6 any 2001:DB8:1:60::/64 (71 matches) sequence 60
deny tcp any 2001:DB8:1:60::/64 eq 22 (9 matches) sequence 70
deny tcp any 2001:DB8:1:60::/64 eq 443 (27 matches) sequence 80
deny tcp any 2001:DB8:1:60::/64 eq 4466 (13 matches) sequence 90
deny udp any 2001:DB8:1:60::/64 eq 3799 (55 matches) sequence 100
deny udp any 2001:DB8:1:60::/64 eq 514 (12 matches) sequence 101
permit icmp any any nd-ns (80 matches) sequence 102
permit icmp any any nd-na (80 matches) sequence 103
deny ipv6 any 2001:DB8:1:60::/64 (5 matches) sequence 104
In the preceding example, access list IPv6-Infrastructure-ACL-Policy has dropped
- 9 SSH packets on TCP port 22 for access control list entry (ACE) Line 70.
- 27 HTTPS packets on TCP port 443 for access control list entry (ACE) Line 80.
- 13 packets on TCP port 4466 for access control list entry (ACE) line 90.
- 55 TCP packets on UDP port 3799 for access control list entry (ACE) line 100.
- 12 SYSLOG packets on UDP port 514 for access control list entry (ACE) line 101.
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: 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 01 0984 0800 9
Gi0/0 192.168.11.54 Gi0/1 192.168.60.158 01 0911 0000 4
Gi0/0 192.168.10.201 Gi0/1 192.168.60.102 06 0984 0016 1
Gi0/0 192.168.10.201 Gi0/1 192.168.60.102 06 0984 01BB 1
Gi0/0 192.168.10.201 Gi0/1 192.168.60.102 11 0984 0ED7 1
Gi0/0 192.168.11.54 Gi0/1 192.168.60.158 06 0911 0016 3
Gi0/1 192.168.150.60 Gi0/0 10.89.16.226 06 0016 12CA 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 SSH on TCP port 22 (hex value 0016), HTTPS on TCP port 443(hex value 01BB), UDP port 3799(hex value 0ED7) as well as ICMP echo requests and echo replies (hex values 0800 and 0000) respectively.
As shown in the following example, to view only the SSH packets on TCP port 22 (hex value 0016), and the TCP port 4466 packets (hex value 1172) , use the show ip cache flow | include SrcIf|_06_.*(0016|1172)_ command to display the related Cisco NetFlow records:
TCP Flows
router#show ip cache flow | include SrcIf|_06_.*(0016|1172)
SrcIf SrcIPaddress DstIf DstIPaddress Pr SrcP DstP Pkts
Gi0/0 192.168.10.201 Gi0/1 192.168.60.102 06 0984 0016 1
Gi0/0 192.168.11.54 Gi0/1 192.168.60.158 06 0911 0016 3
Gi0/0 192.168.10.201 Gi0/1 192.168.60.102 06 0984 1172 1
Gi0/0 192.168.11.54 Gi0/1 192.168.60.158 06 0911 1172 3
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 Go0/1 0x06 0x16C4 0x0016 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...28::21 Gi0/1 0x11 0x0000 0x0ED7 1168
2001:DB...6A:5BA6 Gi0/0 2001:DB...128::2 Gi0/1 0x06 0x160A 0x0016 1597
2001:DB...06::201 Gi0/0 2001:DB...28::20 Go0/1 0x06 0x16C4 0x1172 1466
2001:DB...6A:5BA6 Gi0/0 2001:DB...128::3 Gi0/1 0x3A 0x0000 0x8000 1155
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 SSH on TCP port 22 (hex value 0016), UDP port 3799 (hex value 0ED7), TCP on port 4466 (hex value 1172) .
As shown in the following example, to view only the SSH packets on TCP port 22 (hex value 0016), use the show ipv6 flow cache | include SrcIf|_06_.*0016_ command to display the related Cisco NetFlow records:
TCP Flows
router#show ipv6 flow cache | include SrcIf|_06_.*0016_
SrcAddress InpIf DstAddress OutIf Prot SrcPrt DstPrt Packets
2001:DB...06::201 Gi0/0 2001:DB...28::20 Local 0x06 0x16C4 0x0016 1464
2001:DB...6A:5BA6 Gi0/0 2001:DB...128::2 Gi0/1 0x06 0x160A 0x0016 1597
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 22 Gi0/0 Gi0/1 10128 6
192.168.10.201 192.168.60.102 1316 443 Gi0/0 Gi0/1 1898 6
192.168.10.201 192.168.60.102 1456 4466 Gi0/0 Gi0/1 1128 6
192.168.10.17 192.168.60.97 4231 514 Gi0/0 Gi0/1 14606 17
192.168.10.17 192.168.60.97 4231 3799 Gi0/0 Gi0/1 10223 17
10.88.226.1 192.168.202.22 2678 53 Gi0/0 Gi0/1 10567 17
10.89.16.226 192.168.150.60 3562 80 Gi0/0 Gi0/1 30012 6
To view only the SSH packets on TCP port 22, use the show flow monitor FLOW-MONITOR-ipv4 cache format table | include IPV4 DST ADDR |_22_.*_6_ 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 22 Gi0/0 Gi0/0 1237 6
2001:DB...06::201 2001:DB...28::20 1890 443 Gi0/0 Gi0/0 5009 6
2001:DB...06::201 2001:DB...28::20 1043 4466 Gi0/0 Gi0/0 501 6
2001:DB...06::201 2001:DB...28::20 2044 3799 Gi0/0 Gi0/0 4522 17
2001:DB...06::201 2001:DB...28::20 2856 514 Gi0/0 Gi0/0 486 17
To permit display of the full 128-bit IPv6 address, use the terminal width 132 exec mode command.
To view only the SSH packets on TCP port 22, use the show flow monitor FLOW-MONITOR-ipv6 cache format table | include IPV6 DST ADDR|_22_.*_6_ 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 SSH packets on TCP ports 22, TCP 443, UDP port 3799, and ICMP echo requests that are sent to affected ASA-CX management interfaces, and additionally TCP Port 446 and UDP port 514 requests that are sent to affected PRSM server management interfaces. 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 protocol and port
!
access-list tACL-Policy extended permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 22
access-list tACL-Policy extended permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 443
access-list tACL-Policy extended permit udp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 3799
access-list tACL-Policy extended permit icmp host 192.168.100.1 192.168.60.0 0.0.0.255 8
access-list tACL-Policy extended permit tcp host 192.168.100.1 host 192.168.60.6 eq 4466
access-list tACL-Policy extended permit udp host 192.168.100.1 host 192.168.60.6 eq 514
!
!-- 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 0.0.0.255 eq 22
access-list tACL-Policy extended deny tcp any 192.168.60.0 0.0.0.255 eq 443
access-list tACL-Policy extended deny udp any 192.168.60.0 0.0.0.255 eq 3799
access-list tACL-Policy extended deny tcp any host 192.168.60.6 eq 4466
access-list tACL-Policy extended deny udp any host 192.168.60.6 eq 514
!
!-- Permit or deny all other Layer 3 and Layer 4 traffic in accordance
!-- with existing security policies and configurations
access-list tACL-Policy extended permit icmp any any nd-ns
access-list tACL-Policy extended permit icmp any any nd-na
!
!-- Explicit deny for all other IP traffic
!
access-list tACL-Policy extended deny ip any any
access-group tACL-Policy in interface outside
access-group IPv6-tACL-Policy in interface outside
!
!-- Create the corresponding IPv6 tACL
!
!-- Include explicit permit statements for trusted sources
!-- that require access on the vulnerable protocols and ports
!
ipv6 access-list IPv6-tACL-Policy permit tcp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 22
ipv6 access-list IPv6-tACL-Policy permit tcp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 443
ipv6 access-list IPv6-tACL-Policy permit tcp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 4466
ipv6 access-list IPv6-tACL-Policy permit udp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 3799
ipv6 access-list IPv6-tACL-Policy permit udp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 514
ipv6 access-list IPv6-tACL-Policy permit icmp6 host 2001:DB8::100:1 2001:DB8:1:60::/64
!
!-- 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 22
ipv6 access-list IPv6-tACL-Policy deny tcp any 2001:DB8:1:60::/64 eq 443
ipv6 access-list IPv6-tACL-Policy deny tcp any 2001:DB8:1:60::/64 eq 4466
ipv6 access-list IPv6-tACL-Policy deny udp any 2001:DB8:1:60::/64 eq 3799
ipv6 access-list IPv6-tACL-Policy deny udp any 2001:DB8:1:60::/64 eq 514
!
!-- Permit or deny all other Layer 3 and Layer 4 traffic in accordance
!-- with existing security policies and configurations
!
ipv6 access-list IPv6-tACL-Policy permit icmp any any nd-ns
ipv6 access-list IPv6-tACL-Policy permit icmp any any nd-na
!-- Explicit deny for all other IP traffic
!
ipv6 access-list IPv6-tACL-Policy deny ip any any
!
!--
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 SSH packets sent to TCP port 22, TCP 443, UDP port 3799, and ICMP echo requests that are sent to affected ASA-CX management interfaces, and additionally TCP Port 446 and UDP port 514 requests that are sent to affected PRSM server management interfaces 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; 14 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 ssh (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 https (hitcnt=13)
access-list tACL-Policy line 3 extended permit udp host 192.168.100.1 192.168.60.0 255.255.255.0
eq 3799 (hitcnt=8)
access-list tACL-Policy line 4 extended permit icmp host 192.168.100.1 192.168.60.0 255.255.255.0 8
(hitcnt=8)
access-list tACL-Policy line 5 extended permit tcp host 192.168.100.1 192.168.60.6 255.255.255.255
eq 4466 (hitcnt=8)
access-list tACL-Policy line 6 extended permit udp host 192.168.100.1 192.168.60.6 255.255.255.255
eq syslog (hitcnt=8)
access-list tACL-Policy line 7 extended deny tcp any 192.168.60.0 0.0.0.255 eq ssh (hitcnt=9)
access-list tACL-Policy line 8 extended deny tcp any 192.168.60.0 0.0.0.255 eq https (hitcnt=27)
access-list tACL-Policy line 9 extended deny udp any 192.168.60.0 0.0.0.255 eq 3799 (hitcnt=13)
access-list tACL-Policy line 10 extended deny tcp any 192.168.60.6 0.0.0.0 eq 4466 (hitcnt=11)
access-list tACL-Policy line 11 extended deny udp any 192.168.60.6 0.0.0.0 eq syslog (hitcnt=12)
access-list tACL-Policy line 12 extended permit icmp any any nd-ns (hitcnt=144)
access-list tACL-Policy line 13 extended permit icmp any any nd-na (hitcnt=128)
access-list tACL-Policy line 14 extended deny ip any any (hitcnt=8)
In the preceding example, access list tACL-Policy has dropped
- 9 SSH packets on TCP port 22 for access control list entry (ACE) line 7
- 27 HTTPS packets on TCP port 443 for ACE line 8
- 13 packets on UDP port 3799 for ACE line 9
- 11 TCP packets on TCP port 4466 for ACE line 10
- 12 SYSLOG packets on UDP port 514 for ACE line 11
firewall#show access-list IPv6-tACL-Policy
ipv6 access-list IPv6-tACL-Policy; 14 elements; name hash: 0x566a4229
ipv6 access-list IPv6-tACL-Policy line 1 permit tcp host 2001:DB8::100:1 2001:DB8:1:60::/64
eq 22 (hitcnt=52)
ipv6 access-list IPv6-tACL-Policy line 2 permit tcp host 2001:DB8::100:1 2001:DB8:1:60::/64
eq 443 (hitcnt=59)
ipv6 access-list IPv6-tACL-Policy line 3 permit tcp host 2001:DB8::100:1 2001:DB8:1:60::/64
eq 4466 (hitcnt=12)
ipv6 access-list IPv6-tACL-Policy line 4 permit udp host 2001:DB8::100:1 2001:DB8:1:60::/64
eq 3799 (hitcnt=22)
ipv6 access-list IPv6-tACL-Policy line 5 permit udp host 2001:DB8::100:1 2001:DB8:1:60::/64
eq 514 (hitcnt=11)
ipv6 access-list IPv6-tACL-Policy line 6 permit icmp6 host 2001:DB8::100:1 2001:DB8:1:60::/64
(hitcnt=19)
ipv6 access-list IPv6-tACL-Policy line 7 deny tcp any 2001:DB8:1:60::/64 eq 22 (hitcnt=53)
ipv6 access-list IPv6-tACL-Policy line 8 deny tcp any 2001:DB8:1:60::/64 eq 443 (hitcnt=133)
ipv6 access-list IPv6-tACL-Policy line 9 deny tcp any 2001:DB8:1:60::/64 eq 4466 (hitcnt=11)
ipv6 access-list IPv6-tACL-Policy line 10 deny udp any 2001:DB8:1:60::/64 eq 3799 (hitcnt=35)
ipv6 access-list IPv6-tACL-Policy line 11 deny udp any 2001:DB8:1:60::/64 eq 514 (hitcnt=159)
ipv6 access-list IPv6-tACL-Policy line 12 permit icmp any any nd-ns (hitcnt=19)
ipv6 access-list IPv6-tACL-Policy line 13 permit icmp any any nd-na (hitcnt=19)
ipv6 access-list IPv6-tACL-Policy line 14 deny ipv6 any 2001:DB8:1:60::/64 (hitcnt=89)
In the preceding example, access list IPv6-tACL-Policy has dropped
the following packets received from an untrusted host or network:
- 53 SSH packets on TCP port 22 for ACE line 7
- 133 HTTPS packets on TCP port 443 for ACE line 8
- 11 packets on TCP port 4466 for ACE line 9
- 35 packets on UDP port 3799 for ACE line 10
- 159 SYSLOG packets on UDP port 514 for ACE line 11
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 6 2012 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.18/2944
dst inside:192.168.60.191/ssh by access-group "tACL-Policy"
Sep 6 2012 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.200/2945
dst inside:192.168.60.33/443 by access-group "tACL-Policy"
Sep 6 2012 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.200/2946
dst inside:192.168.60.33/4466 by access-group "tACL-Policy"
Sep 6 2012 00:15:13: %ASA-4-106023: Deny udp src outside:192.0.2.200/2947
dst inside:192.168.60.33/514 by access-group "tACL-Policy"
Sep 6 2012 00:15:13: %ASA-4-106023: Deny udp src outside:192.0.2.200/2948
dst inside:192.168.60.33/3799 by access-group "tACL-Policy"
firewall#
In the preceding example, the messages logged for the tACL tACL-Policy show SSH packets for TCP port 22 , packets for TCP port 443, packets for TCP port 4466, Syslog packets for UDP port 514, and packets for UDP port 3799 sent to the address block assigned to the 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.
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 port 22
- Use the Destination Service event filter to filter objects that contain TCP port 443
- Use the Destination Service event filter to filter objects that contain TCP port 4466
- Use the Destination Service event filter to filter objects that contain UDP port 3799
- Use the Destination Service event filter to filter objects that contain UDP port 514
For more information about Cisco Security Manager Events, refer to the Filtering and Querying Events section of the Cisco Security Manager User Guide.
Cisco Security Manager Report Manager
Beginning in software version 4.1, Cisco Security Manager supports the Report Manager, the Cisco IPS event reporting feature. This feature allows an administrator to define reports based on Cisco IPS events of interest. Reports can be scheduled or users can run ad hoc reports as required.
In the Report Manager, the Top Services report can be used with the following configuration to generate a report of events that indicate potential attempts to exploit the vulnerability that is described in this document:
- Use the Destination IP network 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)
- Set an action of Deny on the Criteria settings page
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.
