Cisco Applied Mitigation Bulletin

Identifying and Mitigating Exploitation of the Multiple Vulnerabilities in Cisco ASA 5500 Series Adaptive Security Appliances

Advisory ID: cisco-amb-20100217-asa

http://tools.cisco.com/security/center/content/CiscoAppliedMitigationBulletin/cisco-amb-20100217-asa

Revision 1.1

For Public Release 2010 February 17 16:00  UTC (GMT)


Contents

Cisco Response
Device-Specific Mitigation and Identification
Additional Information
Revision History
Cisco Security Procedures
Related Information

Cisco Response

This Applied Mitigation Bulletin is a companion document to the PSIRT Security Advisory Multiple Vulnerabilities in Cisco ASA 5500 Series Adaptive Security Appliances and provides identification and mitigation techniques that administrators can deploy on Cisco network devices.

Vulnerability Characteristics

There are multiple vulnerabilities in Cisco ASA 5500 Series Adaptive Security Appliances. The following subsections summarize these vulnerabilities:

TCP Connection Exhaustion Denial of Service Vulnerability: This vulnerability can be exploited remotely without authentication and without end-user interaction. Successful exploitation of this vulnerability may result in a denial of service (DoS) condition. Repeated attempts to exploit this vulnerability could result in a sustained DoS condition.

The attack vectors for exploitation are through packets using the following protocols and ports:

  • HTTP and Virtual HTTP using TCP port 80
  • Cisco Adaptive Security Device Manager (ASDM) and Remote Access SSL VPNs using TCP port 443
  • Telnet and Virtual Telnet using TCP port 23
  • SSH using TCP port 22
  • Transport Layer Security (TLS) Proxy for Encrypted Voice Inspection using TCP port 2443

Note that Remote Access SSL VPNs and TLS Proxy for Encrypted Voice Inspection will not be addressed in this AMB because no network mitigations are available. These are device-specific vulnerabilities or the malicious sources are unable to be identified.

This vulnerability has been assigned CVE identifier CVE-2010-0149.

SIP Inspection Denial of Service Vulnerabilities: These vulnerabilities can be exploited remotely without authentication and without end-user interaction. Successful exploitation of these vulnerabilities may cause the affected device to reload, resulting in a denial of service (DoS) condition. Repeated attempts to exploit these vulnerabilities could result in a sustained DoS condition.

The attack vectors for exploitation are through packets using the following protocols and ports:

  • SIP using TCP port 5060
  • SIP using UDP port 5060

An attacker could exploit this vulnerability using spoofed packets.

Note that these vulnerabilities will not be addressed in this AMB. No network mitigations are available because of the nature of these vulnerabilities.

These vulnerabilities have been assigned CVE identifiers CVE-2010-0150 and CVE-2010-0569.

SCCP Inspection Denial of Service Vulnerability: This vulnerability can be exploited remotely without authentication and without end-user interaction. Successful exploitation of this vulnerability may cause the affected device to reload, resulting in a denial of service (DoS) condition. Repeated attempts to exploit this vulnerability could result in a sustained DoS condition. The attack vector for exploitation is through SCCP packets using TCP port 2000.

Note that this vulnerability will not be addressed in this AMB. No network mitigations are available because of the nature of this vulnerability.

This vulnerability has been assigned CVE identifier CVE-2010-0151.

WebVPN DTLS Denial of Service Vulnerability: This vulnerability can be exploited remotely without authentication and without end-user interaction. Successful exploitation of this vulnerability may cause the affected device to reload, resulting in a denial of service (DoS) condition. Repeated attempts to exploit this vulnerability could result in a sustained DoS condition. The attack vector for exploitation is through DTLS packets using UDP port 443. An attacker could exploit this vulnerability using spoofed packets.

Note that this vulnerability will not be addressed in this AMB. No network mitigations are available because of the nature of this vulnerability.

This vulnerability has been assigned CVE identifier CVE-2010-0565.

Crafted TCP Segment Denial of Service Vulnerability: This vulnerability can be exploited remotely without authentication and without end-user interaction. Successful exploitation of this vulnerability may cause the affected device to reload, resulting in a denial of service (DoS) condition. Repeated attempts to exploit this vulnerability could result in a sustained DoS condition. The attack vector for exploitation is through TCP packets. An attacker could exploit this vulnerability using spoofed packets.

Note that this vulnerability will not be addressed in this AMB. No network mitigations are available because of the nature of this vulnerability.

This vulnerability has been assigned CVE identifier CVE-2010-0566.

Crafted IKE Message Denial of Service Vulnerability: This vulnerability can be exploited remotely without authentication and without end-user interaction. Successful exploitation of this vulnerability may result in a denial of service (DoS) condition. Repeated attempts to exploit this vulnerability could result in a sustained DoS condition. The attack vector for exploitation is through IKE packets using UDP port 4500. An attacker could exploit this vulnerability using spoofed packets.

Note that this vulnerability will not be addressed in this AMB. No network mitigations are available because of the nature of this vulnerability.

This vulnerability has been assigned CVE identifier CVE-2010-0567.

NTLMv1 Authentication Bypass Vulnerability: This vulnerability can be exploited remotely without authentication and requires end-user interaction. Successful exploitation of this vulnerability will result in unauthorized access to the network or the security appliance. Successful exploitation of this vulnerability may allow authentication bypass, which enables an attacker to obtain access to the network without providing valid credentials.

Note that this vulnerability will not be addressed in this AMB. No network mitigations are available because of the nature of this vulnerability.

This vulnerability has been assigned CVE identifier CVE-2010-0568.

Information about vulnerable, unaffected, and fixed software is available in the PSIRT Security Advisory, which is available at the following link: http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20100217-asa.

Mitigation Technique Overview

Cisco devices provide several countermeasures for these vulnerabilities. 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, the Cisco PIX 500 Series Security Appliance, and the Firewall Services Module (FWSM) for Cisco Catalyst 6500 Series switches and Cisco 7600 Series routers using Transit access control lists (tACLs).

This protection mechanism filters and drops 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 and Cisco PIX security appliances, and 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 these vulnerabilities. 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 Caution: The effectiveness of any mitigation technique is dependent 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 these vulnerabilities when the attack originates from a trusted source address.

The iACL policy denies unauthorized packets that are sent to affected devices via the following protocols:

  • Cisco Adaptive Security Device Manager (ASDM) SSL using TCP port 443
  • HTTP and/or virtual HTTP using TCP port 80
  • Telnet and/or virtual Telnet using TCP port 23
  • SSH using TCP port 22

Note: Remote Access SSL VPNs are not addressed in this AMB because no network mitigations are available. Any examples including TCP port 443 refer to Cisco ASDM only. In addition to that, the user can customize the port to be used for ASDM connections to be other than TCP port 443 - in that scenario, references to TCP port 443 would need to be changed to match the port selected.

In the following example, 192.168.60.0/24 is 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
    
  !
  !-- Include explicit permit statements for trusted sources 
  !-- that require access on the vulnerable ports
  !
 
  permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 443
  permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 80
  permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 23
  permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 22
  
  
  !
  !-- 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 443
  deny tcp any 192.168.60.0 0.0.0.255 eq 80
  deny tcp any 192.168.60.0 0.0.0.255 eq 23
  deny tcp any 192.168.60.0 0.0.0.255 eq 22
  
  
  ! 
  !-- 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
  ! 
  !-- Apply iACL to interfaces in the ingress direction 
  !
 
 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 higher layer protocol packets, on their respective ports, 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 these vulnerabilities. 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 443
      20 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 80
      30 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 23
      40 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 22
      50 deny tcp any 192.168.60.0 0.0.0.255 eq 443 (344 matches)
      60 deny tcp any 192.168.60.0 0.0.0.255 eq 80 (238 matches)
      70 deny tcp any 192.168.60.0 0.0.0.255 eq 23 (11 matches)
      80 deny tcp any 192.168.60.0 0.0.0.255 eq 22 (177 matches)
      90 deny ip any 192.168.60.0 0.0.0.255 (352 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:

  • 344 SSL packets on TCP port 443 for ACE line 50
  • 238 HTTP packets on TCP port 80 for ACE line 60
  • 11 Telnet packets on TCP port 23 for ACE line 70
  • 177 SSH packets on TCP port 22 for ACE line 80

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.

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 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 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 Applied Intelligence white paper.

Cisco IOS NetFlow

Identification: Traffic Flow Identification Using NetFlow Records

Administrators can configure Cisco IOS NetFlow on Cisco IOS routers and switches to aid in the identification of traffic flows that may be attempts to exploit these vulnerabilities. Administrators are advised to investigate flows to determine whether they are attempts to exploit these vulnerabilities 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         192.168.10.202  Gi0/1         192.168.60.103  06 0984 01BB    63
Gi0/0         192.168.31.69   Gi0/1         192.168.60.139  06 0911 0050    44
Gi0/1         192.168.150.61  Gi0/0         10.89.16.227    11 0016 12CA     1
Gi0/0         192.168.13.98   Gi0/1         192.168.60.29   06 0B3E 0017    16
Gi0/0         192.168.50.18   Gi0/1         192.168.60.98   06 0B89 0016    12
Gi0/0         10.88.226.2     Gi0/1         192.168.202.22  11 007B 007B     2
Gi0/0         10.89.16.227    Gi0/1         192.168.150.61  06 12CA 0016     2
router#

In the preceding example, there are multiple flows for SSL packets on TCP port 443 (hex value 01BB), HTTP packets on TCP port 80 (hex value 0050), Telnet packets on TCP port 23 (hex value 0017), and SSH packets on TCP port 22 (hex value 0016).

To view only the traffic flows for the packets on the preceding list, the command show ip cache flow | include SrcIf|_06_.*(01BB|0050|0017|0016)_ will display the related TCP NetFlow records as shown here:

router#show ip cache flow | include SrcIf|_06_.*(01BB|0050|0017|0016)_
SrcIf         SrcIPaddress     DstIf         DstIPaddress    Pr SrcP DstP  Pkts
Gi0/0         192.168.10.202   Gi0/1         192.168.60.103  06 0984 01BB    63
Gi0/0         192.168.31.69    Gi0/1         192.168.60.139  06 0911 0050    44
Gi0/0         192.168.13.98    Gi0/1         192.168.60.29   06 0B3E 0017    16
Gi0/0         192.168.50.18    Gi0/1         192.168.60.98   06 0B89 0016    12
router#

Cisco ASA, PIX, and 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 these vulnerabilities when the attack originates from a trusted source address.

The tACL policy denies unauthorized packets that are sent to affected devices via the following protocols:

  • Cisco Adaptive Security Device Manager (ASDM) SSL using TCP port 443
  • HTTP and/or virtual HTTP using TCP port 80
  • Telnet and/or virtual Telnet using TCP port 23
  • SSH using TCP port 22

Note: Remote Access SSL VPNs are not addressed in this AMB because no network mitigations are available. Any examples including TCP port 443 refer to Cisco ASDM only. In addition to that, the user can customize the port to be used for ASDM connections to be other than TCP port 443 - in that scenario, references to TCP port 443 would need to be changed to match the port selected.

Note that the tACL should be configured on a firewall that is upstream of the vulnerable firewall(s) to prevent the unauthorized packets from accessing the affected firewall(s).

In the following example, 192.168.60.0/24 is 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.


!
!-- Include explicit permit statements for trusted sources
!-- that require access on the vulnerable ports
!

access-list tACL-Policy extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq 443
access-list tACL-Policy extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq 80
access-list tACL-Policy extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq 23
access-list tACL-Policy extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq 22


!
!-- 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 443
access-list tACL-Policy extended deny tcp any 192.168.60.0 255.255.255.0 eq 80
access-list tACL-Policy extended deny tcp any 192.168.60.0 255.255.255.0 eq 23
access-list tACL-Policy extended deny tcp any 192.168.60.0 255.255.255.0 eq 22


!
!-- 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


!
!-- Apply tACL to interface(s) in the ingress direction
!

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 higher-layer protocol packets on their respective ports that have been filtered. Administrators are advised to investigate filtered packets to determine whether they are attempts to exploit these vulnerabilities. Example output for show access-list tACL-Policy follows:

firewall#show access-list tACL-Policy
access-list tACL-Policy; 9 elements
access-list tACL-Policy line 1 extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq https (hitcnt=455)  
access-list tACL-Policy line 2 extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq www (hitcnt=332)  
access-list tACL-Policy line 3 extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq telnet (hitcnt=112)  
access-list tACL-Policy line 4 extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq ssh (hitcnt=75)  
access-list tACL-Policy line 5 extended deny tcp any 192.168.60.0 255.255.255.0 eq https (hitcnt=44)
access-list tACL-Policy line 6 extended deny tcp any 192.168.60.0 255.255.255.0 eq www (hitcnt=35)
access-list tACL-Policy line 7 extended deny tcp any 192.168.60.0 255.255.255.0 eq telnet (hitcnt=86)
access-list tACL-Policy line 8 extended deny tcp any 192.168.60.0 255.255.255.0 eq ssh (hitcnt=31)   
access-list tACL-Policy line 9 extended deny ip any any (hitcnt=672) 
firewall#

In the preceding example, access list tACL-Policy has dropped the following packets received from an untrusted host or network:

  • 44 SSL packets on TCP port 443 for ACE line 5
  • 35 HTTP packets on TCP port 80 for ACE line 6
  • 86 Telnet packets on TCP port 23 for ACE line 7
  • 31 SSH packets on TCP port 22 for ACE line 8

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 Security Appliance System Log Message - 106023.

Information about configuring syslog for the Cisco ASA 5500 Series Adaptive Security Appliance or the Cisco PIX 500 Series Security Appliance is in Monitoring the Security Appliance - Configuring and Managing Logs. 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 vulnerabilities that are 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
  Feb 17 2010 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.18/2944 
         dst inside:192.168.60.191/443 by access-group "tACL-Policy"
  Feb 17 2010 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.200/2945 
         dst inside:192.168.60.33/80 by access-group "tACL-Policy"
  Feb 17 2010 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.99/2946 
         dst inside:192.168.60.240/23 by access-group "tACL-Policy"
  Feb 17 2010 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.100/2947 
         dst inside:192.168.60.115/22 by access-group "tACL-Policy"
firewall#

In the preceding example, the messages logged for the tACL tACL-Policy show higher-layer protocol packets for the following protocols and ports sent to the address block assigned to the affected devices:

  • SSL using TCP port 443
  • HTTP and/or virtual HTTP using TCP port 80
  • Telnet and/or virtual Telnet using TCP port 23
  • SSH using TCP port 22

Additional information about syslog messages for ASA and PIX security appliances is in Cisco Security Appliance System Log Messages. Additional information about syslog messages for the 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 Applied Intelligence white paper.

Cisco Intrusion Prevention System

Mitigation: Cisco IPS Signature Event Actions

Administrators can use Cisco Intrusion Prevention System (IPS) appliances and services modules to provide threat detection and help prevent attempts to exploit the vulnerability that is described in this document. This vulnerability may be detected by the following signatures:

  • 24219/0 - Long SIP REGISTER Message
  • 24279/0 - Malformed SIP Packet

24219/0 - Long SIP REGISTER Message

Beginning with signature update S470 for sensors running Cisco IPS version 6.x and greater, the vulnerability can be detected by signature 24219/0 (Signature Name: Long SIP REGISTER Message). Signature 24219/0 is enabled by default, triggers a Medium severity event, has a signature fidelity rating (SFR) of 85, and is configured with a default event action of produce-alert.

Signature 24219/0 fires when upon detecting an attempt to exploit a SIP inspection vulnerability in Cisco ASA 5500 product. Firing of this signature may indicate a potential exploit of the vulnerability.

24279/0 - Malformed SIP Packet

Beginning with signature update S470 for sensors running Cisco IPS version 6.x and greater, the vulnerability can be detected by signature 24279/0 (Signature Name: Malformed SIP Packet). Signature 24279/0 is enabled by default, triggers a Medium severity event, has a signature fidelity rating (SFR) of 85, and is configured with a default event action of produce-alert.

Signature 24279/0 fires upon detecting an attempt to exploit a SIP inspection vulnerability in Cisco ASA 5500 series products. Firing of this signature may indicate a potential exploit of the vulnerability.

Administrators can configure Cisco IPS sensors to perform an event action when an attack is detected. The configured event action performs preventive or deterrent controls to help protect against an attack that is attempting to exploit the vulnerability that is described in this document.

Exploits that use spoofed IP addresses may cause a configured event action to inadvertently deny traffic from trusted sources.

Cisco IPS sensors are most effective when deployed in inline protection mode combined with the use of an event action. Automatic Threat Prevention for Cisco IPS 6.x and greater sensors that are deployed in inline protection mode provides threat prevention against an attack that is attempting to exploit the vulnerability that is described in this document. Threat prevention is achieved through a default override that performs an event action for triggered signatures with a riskRatingValue greater than 90.

For additional information about the risk rating and threat rating calculation, refer to Risk Rating and Threat Rating: Simplify IPS Policy Management.

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.

Revision History

Revision 1.1

2010-February-17

Added information on using IPS devices for mitigation.

Revision 1.0

2010-February-17

Initial public release.

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.

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