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Cisco Applied Mitigation Bulletin

Identifying and Mitigating Exploitation of the Cisco IOS Software Protocol Translation Vulnerability

 
Threat Type:IntelliShield: Applied Mitigation Bulletin
IntelliShield ID:28001
Version:1
First Published:2013 March 27 16:01 GMT
Last Published:2013 March 27 16:01 GMT
Port: Not available
CVE:CVE-2013-1147
Urgency:Unlikely Use
Credibility:Confirmed
Severity:Mild Damage
Related Resources:
View related Security Advisory
 
 
Version Summary:Cisco Applied Mitigation Bulletin initial public release.
 

Cisco Response

This Applied Mitigation Bulletin is a companion document to the PSIRT Security Advisory Cisco IOS Software Protocol Translation Vulnerability and provides identification and mitigation techniques that administrators can deploy on Cisco network devices.

This document provides identification and mitigation techniques that administrators can deploy on Cisco network devices.

Vulnerability Characteristics

The Cisco IOS protocol translation feature exhibits a vulnerability when processing TCP IP version 4 (IPv4) packets. This vulnerability can be exploited remotely without authentication. Successful exploitation of this vulnerability could cause the affected device to crash. Repeated attempts to exploit this vulnerability could result in a sustained DoS condition. The attack vectors for exploitation are through IPv4 packets using the following protocols and ports:
  • Telnet using TCP port 514
  • Telnet using TCP port 544
An attacker could exploit this vulnerability using spoofed packets.

This vulnerability has been assigned Common Vulnerabilities and Exposures (CVE) identifier CVE-2013-1147.

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)
  • 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:

  • Transit access control lists (tACLs)
  • uRPF

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.

The Cisco Security Manager can also provide visibility through incidents, queries, and event reporting.

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:

Cisco IOS Routers and Switches

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 Telnet IPv4 packets on TCP ports 514 and 544 that are sent to affected devices. In the following example, 192.168.60.0/24 represents the IP address space that is used by the affected devices, and the host at 192.168.100.1 is considered a trusted source that requires 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

  !
  !-- 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 514
  deny tcp any 192.168.60.0 0.0.0.255 eq 544
  !
  !-- 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
  !

interface GigabitEthernet0/0
 ip access-group 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 command will identify the number of Telnet IPv4 packets on TCP port 514 and Telnet IPv4 packets on TCP port 544 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 deny tcp any 192.168.60.0 0.0.0.255 eq 514 (9 matches)
    20 deny tcp any 192.168.60.0 0.0.0.255 eq 544 (18 matches)
    30 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 received from an untrusted host or network:

  • 9 Telnet packets on TCP port 514 for ACE line 10
  • 18 Telnet packets on TCP port 544 for ACE line 20

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.

Mitigation: Spoofing Protection

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 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.

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 white paper.

Mitigation: Spoofing Protection Using 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: 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 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 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 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 type slot/port internal, show cef drop, show ip interface type slot/port show ip cef switching statistics feature, and show ip traffic examples, uRPF has dropped the following 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.

  • 18 IPv4 packets

Cisco IOS NetFlow and Cisco IOS Flexible NetFlow

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  06 0984 0202     1
Gi0/0         192.168.11.54   Gi0/1         192.168.60.158  11 0911 00A1     3
Gi0/1         192.168.150.60  Gi0/0         10.89.16.226    06 0016 0202     1
Gi0/0         192.168.13.97   Gi0/1         192.168.60.28   06 0B3E 0220     5
Gi0/0         192.168.10.17   Gi0/1         192.168.60.97   11 0B89 00A1     1
Gi0/0         10.88.226.1     Gi0/1         192.168.202.22  06 007B 0220     1
Gi0/0         192.168.12.185  Gi0/1         192.168.60.239  11 0BD7 00A1     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 Telnet on TCP port 514 (hex value 0202) and Telnet on TCP port 544 (hex value 0220).

This traffic is sourced from and sent to addresses within the 192.168.60.0/24 address block, which is used for infrastructure 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 Telnet traffic sent on TCP port 514 and Telnet traffic sent on port 544 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 Telnet packets on TCP port 514 (hex value 0202), use the show ip cache flow | include SrcIf |_PrHex_.*(0202|0220)_ command to display the related Cisco NetFlow records:

TCP Flows
router#show ip cache flow | include SrcIf|_PrHex_.*(0202|0220)_
SrcIf         SrcIPaddress     DstIf         DstIPaddress    Pr SrcP DstP  Pkts
Gi0/0         192.168.12.110   Gi0/1         192.168.60.163  06 092A 0202     6
Gi0/0         192.168.11.230   Gi0/1         192.168.60.20   06 0C09 0202     1
Gi0/0         192.168.11.131   Gi0/1         192.168.60.245  06 0B66 0202    18
Gi0/0         192.168.13.7     Gi0/1         192.168.60.162  06 0914 0202     1
Gi0/0         192.168.41.86    Gi0/1         192.168.60.27   06 0B7B 0202     2
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           514      Gi0/0       Gi0/1   1128      6
  192.168.11.54  192.168.60.158           123           123      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           544      Gi0/0       Gi0/1      1      6
  192.168.10.17   192.168.60.97          4231           514      Gi0/0       Gi0/1    146      6
    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 the Telnet packets on TCP port 514 and Telnet packets on port 544, use the show flow monitor FLOW-MONITOR-ipv4 cache format table | include IPV4 DST ADDR |_(514|544)_.*_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.

Cisco ASA, Cisco ASASM, and Cisco FWSM Firewalls

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 Telnet IPv4 packets on TCP port 514 and TCP port 544 that are sent to affected devices. In the following example, 192.168.60.0/24 represents the IP address space that is used by the affected devices, and the host at 192.168.100.1 is considered a trusted source that requires 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.

!
!-- 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 514
access-list tACL-Policy extended deny tcp any 192.168.60.0 255.255.255.0 eq 544
!
!-- 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
!
access-group 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 Telnet IPv4 packets on TCP port 514 and Telnet packets on port 544 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 follows:

firewall#show access-list tACL-Policy
access-list tACL-Policy; 3 elements; name hash: 0x3452703d
access-list tACL-Policy line 1 extended deny tcp any 192.168.60.0 
     255.255.255.0 eq 514 (hitcnt=8)
access-list tACL-Policy line 2 extended deny tcp any 192.168.60.0 
     255.255.255.0 eq 544 (hitcnt=14)
access-list tACL-Policy line 3 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 Telnet packets on TCP port 514 for ACE line 1
  • 14 Telnet packets on TCP port 544 for ACE line 2

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
  Mar 27 2013 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.18/2944 
         dst inside:192.168.60.191/544 by access-group "tACL-Policy"
  Mar 27 2013 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.200/2945 
         dst inside:192.168.60.33/514 by access-group "tACL-Policy"
firewall#

In the preceding example, the messages logged for the tACL tACL-Policy show potentially spoofed Telnet packets for TCP port 514 and Telnet packets for TCP port 544 sent to the address block assigned to the infrastructure 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 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
  Mar 27 2013 00:15:13: %ASA-1-106021: Deny TCP reverse path check from
         192.168.60.1 to 192.168.60.100 on interface outside
  Mar 27 2013 00:15:13: %ASA-1-106021: Deny TCP reverse path check from
         192.168.60.1 to 192.168.60.100 on interface outside
  Mar 27 2013 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.

Cisco Security Manager

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)
  • Use the Destination Service event filter to filter objects that contain TCP port 514 and TCP port 544

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.

Cisco Security Manager Report Manager

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)
  • Set an action of Deny on the Criteria settings page

For more information about Cisco Security Manager IPS Event Reporting refer to the Understanding IPS Top Reports 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 tested 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 Cisco IPS signature or 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 Sig ID and 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

THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.

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/web/about/security/psirt/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

 
Alert History
 
Initial Release


Product Sets
 
The security vulnerability applies to the following combinations of products.

Primary Products:
N/A

Associated Products:
CiscoIOS 12.3T 12.3(8)T, 12.3(8)T1, 12.3(8)T10, 12.3(8)T11, 12.3(8)T2, 12.3(8)T3, 12.3(8)T4, 12.3(8)T5, 12.3(8)T6, 12.3(8)T7, 12.3(8)T8, 12.3(8)T9, 12.3(11)T, 12.3(11)T1, 12.3(11)T10, 12.3(11)T11, 12.3(11)T12, 12.3(11)T2, 12.3(11)T2a, 12.3(11)T3, 12.3(11)T4, 12.3(11)T5, 12.3(11)T6, 12.3(11)T7, 12.3(11)T8, 12.3(11)T9, 12.3(14)T, 12.3(14)T1, 12.3(14)T2, 12.3(14)T3, 12.3(14)T4, 12.3(14)T5, 12.3(14)T6, 12.3(14)T7 | 12.3TO 12.3(11)TO3 | 12.3XL 12.3(11)XL, 12.3(11)XL1, 12.3(11)XL2, 12.3(11)XL3 | 12.3XM 12.3(7)XM | 12.3XR 12.3(7)XR1, 12.3(7)XR2, 12.3(7)XR3, 12.3(7)XR5, 12.3(7)XR6, 12.3(7)XR7 | 12.3XW 12.3(8)XW, 12.3(8)XW1, 12.3(8)XW1a, 12.3(8)XW2, 12.3(8)XW3 | 12.3XX 12.3(8)XX2d, 12.3(8)XX2e | 12.3YA 12.3(8)YA, 12.3(8)YA1 | 12.3YC 12.3(8)YC, 12.3(8)YC1, 12.3(8)YC2, 12.3(8)YC3 | 12.3YF 12.3(11)YF | 12.3YG 12.3(8)YG, 12.3(8)YG1, 12.3(8)YG2, 12.3(8)YG3, 12.3(8)YG4, 12.3(8)YG5, 12.3(8)YG6, 12.3(8)YG7 | 12.3YH 12.3(8)YH | 12.3YI 12.3(8)YI, 12.3(8)YI1, 12.3(8)YI2, 12.3(8)YI3 | 12.3YK 12.3(11)YK, 12.3(11)YK1, 12.3(11)YK2, 12.3(11)YK3 | 12.3YM 12.3(14)YM11 | 12.3YN 12.3(11)YN | 12.3YS 12.3(11)YS, 12.3(11)YS1, 12.3(11)YS2 | 12.3YT 12.3(14)YT, 12.3(14)YT1 | 12.3YU 12.3(14)YU1 | 12.3YX 12.3(14)YX4, 12.3(14)YX9 | 12.3YZ 12.3(11)YZ, 12.3(11)YZ1, 12.3(11)YZ2 | 12.3ZA 12.3(8)ZA, 12.3(8)ZA1 | 12.3ZB 12.3(11)ZB, 12.3(11)ZB1, 12.3(11)ZB2 | 12.4 12.4(1), 12.4(1a), 12.4(1b), 12.4(1c), 12.4(3), 12.4(3a), 12.4(3b), 12.4(3c), 12.4(3d), 12.4(3e), 12.4(3f), 12.4(3g), 12.4(3h), 12.4(3i), 12.4(3j), 12.4(5), 12.4(5a), 12.4(5b), 12.4(5c), 12.4(7), 12.4(7a), 12.4(7b), 12.4(7c), 12.4(7d), 12.4(7e), 12.4(7f), 12.4(7g), 12.4(7h), 12.4(8), 12.4(8a), 12.4(8b), 12.4(8c), 12.4(8d), 12.4(10), 12.4(10a), 12.4(10b), 12.4(10c), 12.4(12), 12.4(12a), 12.4(12b), 12.4(12c), 12.4(13), 12.4(13a), 12.4(13b), 12.4(13c), 12.4(13d), 12.4(13e), 12.4(13f), 12.4(16), 12.4(16a), 12.4(16b), 12.4(17), 12.4(17a), 12.4(17b), 12.4(18), 12.4(18a), 12.4(18b), 12.4(18c), 12.4(18d), 12.4(18e), 12.4(19), 12.4(21), 12.4(21a), 12.4(23), 12.4(23a), 12.4(23b), 12.4(23c), 12.4(23d), 12.4(23e), 12.4(25), 12.4(25a), 12.4(25b), 12.4(25c), 12.4(25d), 12.4(25e), 12.4(25f), 12.4(25g) | 12.4GC 12.4(22)GC1, 12.4(22)GC1a, 12.4(24)GC1, 12.4(24)GC3, 12.4(24)GC3a, 12.4(24)GC4, 12.4(24)GC5 | 12.4M 12.4(5a)M0, 12.4(21a)M1, 12.4(23b)M1 | 12.4MR 12.4(12)MR2, 12.4(16)MR, 12.4(16)MR1, 12.4(16)MR2, 12.4(19)MR, 12.4(19)MR1, 12.4(19)MR2, 12.4(20)MR, 12.4(20)MR2 | 12.4MRA 12.4(20)MRA, 12.4(20)MRA1 | 12.4MRB 12.4(20)MRB, 12.4(20)MRB1 | 12.4SW 12.4(11)SW, 12.4(11)SW1, 12.4(11)SW2, 12.4(11)SW3, 12.4(15)SW, 12.4(15)SW1, 12.4(15)SW2, 12.4(15)SW3, 12.4(15)SW4, 12.4(15)SW5, 12.4(15)SW6, 12.4(15)SW7, 12.4(15)SW8, 12.4(15)SW8a, 12.4(15)SW9 | 12.4T 12.4(2)T, 12.4(2)T1, 12.4(2)T2, 12.4(2)T3, 12.4(2)T4, 12.4(2)T5, 12.4(2)T6, 12.4(4)T, 12.4(4)T1, 12.4(4)T2, 12.4(4)T3, 12.4(4)T4, 12.4(4)T5, 12.4(4)T6, 12.4(4)T7, 12.4(4)T8, 12.4(6)T, 12.4(6)T1, 12.4(6)T10, 12.4(6)T11, 12.4(6)T12, 12.4(6)T2, 12.4(6)T3, 12.4(6)T4, 12.4(6)T5, 12.4(6)T5a, 12.4(6)T5b, 12.4(6)T5c, 12.4(6)T5d, 12.4(6)T5e, 12.4(6)T5f, 12.4(6)T6, 12.4(6)T7, 12.4(6)T8, 12.4(6)T9, 12.4(9)T, 12.4(9)T0a, 12.4(9)T1, 12.4(9)T2, 12.4(9)T3, 12.4(9)T4, 12.4(9)T5, 12.4(9)T6, 12.4(9)T7, 12.4(11)T, 12.4(11)T1, 12.4(11)T2, 12.4(11)T3, 12.4(11)T4, 12.4(15)T, 12.4(15)T1, 12.4(15)T10, 12.4(15)T11, 12.4(15)T12, 12.4(15)T13, 12.4(15)T13b, 12.4(15)T14, 12.4(15)T15, 12.4(15)T16, 12.4(15)T17, 12.4(15)T2, 12.4(15)T3, 12.4(15)T4, 12.4(15)T5, 12.4(15)T6, 12.4(15)T6a, 12.4(15)T7, 12.4(15)T8, 12.4(15)T9, 12.4(20)T, 12.4(20)T1, 12.4(20)T2, 12.4(20)T3, 12.4(20)T4, 12.4(20)T5, 12.4(20)T5a, 12.4(20)T6, 12.4(22)T, 12.4(22)T1, 12.4(22)T2, 12.4(22)T3, 12.4(22)T4, 12.4(22)T5, 12.4(24)T, 12.4(24)T1, 12.4(24)T2, 12.4(24)T3, 12.4(24)T4, 12.4(24)T5, 12.4(24)T6, 12.4(24)T7, 12.4(24)T8 | 12.4XA 12.4(2)XA, 12.4(2)XA1, 12.4(2)XA2 | 12.4XB 12.4(2)XB6 | 12.4XC 12.4(4)XC, 12.4(4)XC1, 12.4(4)XC2, 12.4(4)XC3, 12.4(4)XC4, 12.4(4)XC5, 12.4(4)XC6, 12.4(4)XC7 | 12.4XD 12.4(4)XD, 12.4(4)XD1, 12.4(4)XD10, 12.4(4)XD11, 12.4(4)XD12, 12.4(4)XD2, 12.4(4)XD3, 12.4(4)XD4, 12.4(4)XD5, 12.4(4)XD6, 12.4(4)XD7, 12.4(4)XD8, 12.4(4)XD9 | 12.4XE 12.4(6)XE, 12.4(6)XE1, 12.4(6)XE2, 12.4(6)XE3 | 12.4XG 12.4(9)XG2 | 12.4XJ 12.4(11)XJ, 12.4(11)XJ1, 12.4(11)XJ2, 12.4(11)XJ3, 12.4(11)XJ4, 12.4(11)XJ5, 12.4(11)XJ6 | 12.4XK 12.4(14)XK | 12.4XT 12.4(6)XT, 12.4(6)XT1, 12.4(6)XT2 | 12.4XV 12.4(11)XV, 12.4(11)XV1 | 12.4XW 12.4(11)XW, 12.4(11)XW1, 12.4(11)XW10, 12.4(11)XW2, 12.4(11)XW3, 12.4(11)XW4, 12.4(11)XW5, 12.4(11)XW6, 12.4(11)XW7, 12.4(11)XW8, 12.4(11)XW9 | 12.4XY 12.4(15)XY, 12.4(15)XY1, 12.4(15)XY2, 12.4(15)XY3, 12.4(15)XY4, 12.4(15)XY5 | 12.4XZ 12.4(15)XZ, 12.4(15)XZ1, 12.4(15)XZ2 | 12.4YA 12.4(20)YA, 12.4(20)YA1, 12.4(20)YA2, 12.4(20)YA3 | 12.4YB 12.4(22)YB, 12.4(22)YB1, 12.4(22)YB4, 12.4(22)YB5, 12.4(22)YB6, 12.4(22)YB7, 12.4(22)YB8 | 15.0M 15.0(1)M, 15.0(1)M1, 15.0(1)M2, 15.0(1)M3, 15.0(1)M4, 15.0(1)M5, 15.0(1)M6, 15.0(1)M6a, 15.0(1)M7, 15.0(1)M8, 15.0(1)M9 | 15.0XA 15.0(1)XA, 15.0(1)XA1, 15.0(1)XA2, 15.0(1)XA3, 15.0(1)XA4, 15.0(1)XA5 | 15.1GC 15.1(2)GC, 15.1(2)GC1, 15.1(2)GC2, 15.1(4)GC | 15.1M 15.1(4)M, 15.1(4)M0a, 15.1(4)M0b, 15.1(4)M1, 15.1(4)M2, 15.1(4)M3, 15.1(4)M3a, 15.1(4)M4, 15.1(4)M5 | 15.1T 15.1(1)T, 15.1(1)T1, 15.1(1)T2, 15.1(1)T3, 15.1(1)T4, 15.1(1)T5, 15.1(2)T, 15.1(2)T0a, 15.1(2)T1, 15.1(2)T2, 15.1(2)T2a, 15.1(2)T3, 15.1(2)T4, 15.1(2)T5, 15.1(3)T, 15.1(3)T1, 15.1(3)T2, 15.1(3)T3, 15.1(3)T4 | 15.1XB 15.1(1)XB, 15.1(1)XB1, 15.1(1)XB2, 15.1(1)XB3, 15.1(4)XB4, 15.1(4)XB5, 15.1(4)XB5a, 15.1(4)XB6, 15.1(4)XB7, 15.1(4)XB8a | 15.2GC 15.2(1)GC, 15.2(1)GC1, 15.2(1)GC2, 15.2(2)GC, 15.2(3)GC | 15.2GCA 15.2(3)GCA | 15.2JA 15.2(2)JA, 15.2(2a)JA | 15.2M 15.2(4)M, 15.2(4)M1, 15.2(4)M2 | 15.2T 15.2(1)T, 15.2(1)T1, 15.2(1)T2, 15.2(1)T3, 15.2(1)T3a, 15.2(2)T, 15.2(2)T1, 15.2(2)T2, 15.2(3)T, 15.2(3)T1, 15.2(3)T2 | 15.2XB 15.2(4)XB10 | 15.3T 15.3(1)T




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LEGAL DISCLAIMER
The urgency and severity ratings of this alert are not tailored to individual users; users may value alerts differently based upon their network configurations and circumstances. THE ALERT, AND INFORMATION CONTAINED THEREIN, ARE PROVIDED ON AN "AS IS" BASIS AND DO NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE ALERT, AND INFORMATION CONTAINED THEREIN, OR MATERIALS LINKED FROM THE ALERT, IS AT YOUR OWN RISK. INFORMATION IN THIS ALERT AND ANY RELATED COMMUNICATIONS IS BASED ON OUR KNOWLEDGE AT THE TIME OF PUBLICATION AND IS SUBJECT TO CHANGE WITHOUT NOTICE. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE ALERTS AT ANY TIME.
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