Cisco Security Advisory

Multiple Vulnerabilities in Cisco PIX and Cisco ASA

Advisory ID: cisco-sa-20080604-asa

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080604-asa

Revision 1.0

For Public Release 2008 June 4 16:00  UTC (GMT)


Summary

Multiple vulnerabilities exist in the Cisco ASA 5500 Series Adaptive Security Appliances and Cisco PIX Security Appliances. This security advisory outlines details of these vulnerabilities:

  • Crafted TCP ACK Packet Vulnerability
  • Crafted TLS Packet Vulnerability
  • Instant Messenger Inspection Vulnerability
  • Vulnerability Scan Denial of Service
  • Control-plane Access Control List Vulnerability

The first four vulnerabilities may lead to a denial of service (DoS) condition and the fifth vulnerability may allow an attacker to bypass control-plane access control lists (ACL).

Note:  These vulnerabilities are independent of each other. A device may be affected by one vulnerability and not affected by another.

Cisco has released free software updates that address these vulnerabilities. Workarounds that mitigate some of these vulnerabilities are available.

This advisory is posted at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080604-asa.

Affected Products

Vulnerable Products

The following are the details about each vulnerability described within this advisory.

Crafted TCP ACK Packet Vulnerability

Cisco ASA and Cisco PIX devices are affected by a crafted TCP acknowledgment (ACK) packet vulnerability. Software versions prior to 7.1(2)70 on the 7.1.x release, 7.2(4) on the 7.2.x release, and 8.0(3)10 on the 8.0.x release are affected. Cisco ASA or Cisco PIX security appliances running software version 7.0.x, or 8.1.x are not vulnerable.

Cisco ASA and Cisco PIX devices running versions 7.1.x and 7.2.x with WebVPN, SSL VPN, or ASDM enabled are affected by this vulnerability. Devices running software versions on the 8.0 release that are configured for Telnet, Secure Shell (SSH), WebVPN, SSL VPN, or ASDM enabled are affected by this vulnerability.

Note: Devices running IPv4 and IPv6 are affected by this vulnerability.

Crafted TLS Packet Vulnerability

Cisco ASA and Cisco PIX devices are affected by a crafted TLS request vulnerability if the HTTPS server on the Cisco ASA or Cisco PIX device is enabled and is running software versions prior to 8.0(3)9 on the 8.0.x release or prior to version 8.1(1)1 on the 8.1.x release. Cisco ASA and Cisco PIX appliances running software versions 7.x are not vulnerable.

Instant Messenger Inspection Vulnerability

Cisco ASA and Cisco PIX devices are affected by a crafted packet vulnerability if Instant Messaging Inspection is enabled and the device is running software versions prior to 7.2(4) on the 7.2.x release, 8.0(3)10 on the 8.0.x release, or 8.1(1)2 on the 8.1.x release. Devices running software versions in the 7.0.x and 7.1.x releases are not vulnerable. Additionally, devices that do not have Instant Messaging Inspection enabled are not vulnerable.

Note:  Instant Messaging Inspection is disabled by default.

Vulnerability Scan Denial of Service

Cisco ASA and Cisco PIX devices are affected by a vulnerability (port) scan denial of service vulnerability if the device is running software versions prior to 7.2(3)2 on the 7.2.x release or 8.0(2)17 on the 8.0.x release. Cisco ASA and Cisco PIX devices running software versions 7.0.x, 7.1.x, or 8.1.x are not vulnerable.

Control-plane Access Control List Vulnerability

Cisco ASA and Cisco PIX devices are affected by a vulnerability if the device is configured to use control-plane ACLs and if it is running software versions prior to 8.0(3)9 on the 8.0.x release. Devices running software versions 7.x or 8.1.x are not vulnerable.

Note:  Control-plane ACLs were first introduced in software version 8.0(2). The control-plane ACLs are not enabled by default.

The show version command-line interface (CLI) command can be used to determine if a vulnerable version of the Cisco PIX or Cisco ASA software is running. The following example shows a Cisco ASA Security Appliance that runs software release 8.0(2):

ASA# show version

Cisco Adaptive Security Appliance Software Version 8.0(2)
Device Manager Version 6.0(1)

[...]

Customers who use the Cisco Adaptive Security Device Manager (ASDM) to manage their devices can find the version of the software displayed in the table in the login window or in the upper left corner of the ASDM window.

Products Confirmed Not Vulnerable

The Cisco Firewall Services Module (FWSM) is not affected by any of these vulnerabilities. Cisco PIX security appliances running versions 6.x are not vulnerable. No other Cisco products are currently known to be affected by these vulnerabilities.

Details

This Security Advisory describes multiple distinct vulnerabilities. These vulnerabilities are independent of each other.

1. Crafted TCP ACK Packet Vulnerability

A crafted TCP ACK packet may cause a denial of service condition on the Cisco ASA or Cisco PIX security appliances. Only packets destined to the device (not transiting the device) may trigger the effects of this vulnerability.

Cisco ASA and Cisco PIX devices running versions 7.1.x and 7.2.x with WebVPN, SSL VPN, or ASDM enabled are affected by this vulnerability. Devices running software versions on the 8.0 release that are configured for Telnet, Secure Shell (SSH), WebVPN, SSL VPN, or ASDM enabled are affected by this vulnerability.

The telnet command is used identify the IP addresses from which the security appliance accepts Telnet connections.

ASA(config)# telnet 192.168.10.0 255.255.255.0 inside

In the previous example, the Cisco ASA is configured to accept Telnet connections on the inside interface from the 192.168.10.0/24 network.

Note: You cannot use Telnet to the lowest security interface unless you use Telnet inside an IPSec tunnel.

ASDM management sessions are enabled via the http server enable and http commands.

The ssh command is used identify the IP addresses from which the security appliance accepts SSH connections. For example:

ASA(config)# ssh 192.168.10.0 255.255.255.0 inside

In the previous example the Cisco ASA is configured to accept SSH connections on the inside interface from the 192.168.10.0/24 network.

Clientless WebVPN, SSL VPN Client, and AnyConnect connections are enabled via the webvpn command. For example, the following configuration shows a Cisco ASA with WebVPN configured and enabled. In this case the ASA will listen for WebVPN connections on the default port, TCP port 443:

http server enable                                                              
!
webvpn                                                                          
 enable outside

Note that with this particular configuration, the device is vulnerable to attacks coming from the outside interface.

This vulnerability is documented in Cisco Bug ID CSCsm84110 ( registered customers only) and has been assigned Common Vulnerabilities and Exposures (CVE) identifier CVE-2008-2055.

2. Crafted TLS Packet Vulnerability

Transport Layer Security (TLS) is the replacement for the Secure Socket Layer (SSL) protocol. It is a protocol that provides, via cryptography, secure communications between two end-points.

The Cisco PIX and Cisco ASA security appliances rely on TLS to protect the confidentiality of communications in a variety of scenarios. In all these scenarios, the PIX and ASA may be affected by a vulnerability in the handling of the TLS protocol that may lead to a reload of the device when it processes specially crafted TLS packets.

Note:  Only packets destined to the device (not transiting the device) may trigger the effects of this vulnerability.

The following list contains some of the applications within the Cisco ASA and Cisco PIX devices that use TLS:

  • Clientless WebVPN, SSL VPN Client, and AnyConnect Connections
  • ASDM (HTTPS) Management Sessions
  • Cut-Through Proxy for Network Access
  • TLS Proxy for Encrypted Voice Inspection

Clientless WebVPN, SSL VPN Client, and AnyConnect Connections

Clientless WebVPN, SSL VPN Client, and AnyConnect connections are enabled via the webvpn command. For example, the following configuration shows a Cisco ASA with WebVPN configured and enabled. In this case the ASA will listen for WebVPN connections on the default port, TCP port 443:

http server enable                                                              
!
webvpn                                                                          
 enable outside

Note that with this particular configuration, the device is vulnerable to attacks coming from the outside interface.

ASDM (HTTPS) Management Sessions

ASDM management sessions are enabled via the http server enable and http commands. For example, the following configuration shows an ASA configured for remote HTTPS management:

http server enable
http 192.168.0.0 255.255.255.0 inside

Note that with this particular configuration the device is vulnerable to attacks coming from the inside interface and from the 192.168.0.0/24 IP sub-network.

Cut-Through Proxy for Network Access

The cut-through proxy feature is used to authenticate users before they can access the network. The following is an example of a configuration that requires users to authenticate before they can be granted network access:

access-list auth-proxy extended permit tcp any any eq www
access-list auth-proxy extended permit tcp any any eq telnet
access-list auth-proxy extended permit tcp any any eq https
!
aaa authentication match auth-proxy inside LOCAL
aaa authentication secure-http-client
aaa authentication listener https inside port https

A configuration affected by this vulnerability will contain the command aaa authentication secure-http-client or aaa authentication listener https inside port <port number>. Note that with the configuration in the preceding example, the device is vulnerable to attacks coming from the inside interface.

TLS Proxy for Encrypted Voice Inspection

The TLS proxy for encrypted voice inspection feature allows the security appliance to decrypt, inspect and modify (as needed, for example, performing NAT fixup), and re-encrypt voice signaling traffic while all of the existing VoIP inspection functions for SCCP and Session Initiation Protocol (SIP) protocols are preserved. Once voice signaling is decrypted, the plain-text signaling message is passed to the existing inspection engines. The security appliance accomplishes this by acting as a TLS proxy between the IP phone and Cisco Unified CallManager and Cisco Unified Communications Manager, which implies that TLS sessions are terminating on the security appliance. This is done over TCP ports 2443 and 5061.

To determine whether the Cisco PIX or Cisco ASA security appliance is configured to support inspection of encrypted voice, log in to the device and issue the CLI command show service-policy | include tls. If the output contains the text tls-proxy: active and some statistics, then the device has a vulnerable configuration. The following example shows a vulnerable Cisco ASA Security Appliance:

ASA# show service-policy | include tls
      Inspect: sip tls-proxy myproxy, packet 0, drop 0, reset-drop 0
               tls-proxy: active sess 0, most sess 0, byte 0
      Inspect: skinny tls-proxy myproxy, packet 0, drop 0, reset-drop 0
               tls-proxy: active sess 0, most sess 0, byte 0
ASA#

This vulnerability is documented in Cisco Bug ID CSCsm26841 ( registered customers only) and has been assigned the Common Vulnerabilities and Exposures (CVE) identifier CVE-2008-2056.

3. Instant Messenger Inspection Vulnerability

The Cisco ASA and Cisco PIX Instant Messenger (IM) inspection engine is used to apply fine grained controls on the IM application usage within your network. The Cisco ASA and Cisco PIX is affected by a denial of service vulnerability if the Instant Messaging Inspection is enabled.

More information on the IM inspection feature and its configuration can be found at:

http://www.cisco.com/en/US/docs/security/asa/asa80/configuration/guide/inspect.html#wp1479354

This vulnerability is documented in Cisco Bug ID CSCso22981 ( registered customers only) and has been assigned Common Vulnerabilities and Exposures (CVE) identifier CVE-2008-2057.

4. Vulnerability Scan Denial of Service

The Cisco ASA and Cisco PIX security appliances are affected by a denial of service vulnerability when a vulnerability scan is conducted against TCP port 443. Certain vulnerability (port) scanners will cause the system to reload.

Note:  This vulnerability is affected by traffic destined to the device on TCP port 443. The Cisco ASA and Cisco PIX security appliances use TCP port 443 for Clientless WebVPN, SSL VPN Client, AnyConnect client connections, HTTPS Management Sessions, Cut-Through Proxy for Network Access, and TLS Proxy for Encrypted Voice Inspection. Please refer to the details of the Crafted TLS Packet Vulnerability for additional information on these services.

This vulnerability is documented in Cisco Bug ID CSCsj60659 ( registered customers only) and has been assigned Common Vulnerabilities and Exposures (CVE) identifier CVE-2008-2058.

5. Control-plane Access Control List Vulnerability

Control-plane ACLs are designed to protect traffic destined to the security appliance. A vulnerability exist in the Cisco ASA and Cisco PIX security appliances where a control-plane ACL may not work after it is initially configured on the device.

The following example uses the show running-config | include control-plane command to determine if a control-plane ACL is configured on the device:

ASA# show running-config | include control-plane
access-group 101 in interface inside control-plane
ASA#

This vulnerability is documented in Cisco Bug ID CSCsm67466 ( registered customers only) and has been assigned Common Vulnerabilities and Exposures (CVE) identifier CVE-2008-2059.

Vulnerability Scoring Details

Cisco has provided scores for the vulnerabilities in this advisory based on the Common Vulnerability Scoring System (CVSS). The CVSS scoring in this Security Advisory is done in accordance with CVSS version 2.0.

CVSS is a standards-based scoring method that conveys vulnerability severity and helps determine urgency and priority of response.

Cisco has provided a base and temporal score. Customers can then compute environmental scores to assist in determining the impact of the vulnerability in individual networks.

Cisco has provided an FAQ to answer additional questions regarding CVSS at

http://www.cisco.com/web/about/security/intelligence/cvss-qandas.html.

Cisco has also provided a CVSS calculator to help compute the environmental impact for individual networks at

http://intellishield.cisco.com/security/alertmanager/cvss.

CSCsm84110 - Crafted TCP ACK Packet Vulnerability

Calculate the environmental score of CSCsm84110

CVSS Base Score - 7.8

Access Vector

Access Complexity

Authentication

Confidentiality Impact

Integrity Impact

Availability Impact

Network

Low

None

None

None

Complete

CVSS Temporal Score - 6.4

Exploitability

Remediation Level

Report Confidence

Functional

Official-Fix

Confirmed

CSCsm26841 - Crafted TLS Packet Vulnerability

Calculate the environmental score of CSCsm26841

CVSS Base Score - 7.8

Access Vector

Access Complexity

Authentication

Confidentiality Impact

Integrity Impact

Availability Impact

Network

Low

None

None

None

Complete

CVSS Temporal Score - 6.4

Exploitability

Remediation Level

Report Confidence

Functional

Official-Fix

Confirmed

CSCso22981 - Instant Messenger Inspection Vulnerability

Calculate the environmental score of CSCso22981

CVSS Base Score - 7.8

Access Vector

Access Complexity

Authentication

Confidentiality Impact

Integrity Impact

Availability Impact

Network

Low

None

None

None

Complete

CVSS Temporal Score - 6.4

Exploitability

Remediation Level

Report Confidence

Functional

Official-Fix

Confirmed

CSCsj60659 - Vulnerability Scan Denial of Service

Calculate the environmental score of CSCsj60659

CVSS Base Score - 7.8

Access Vector

Access Complexity

Authentication

Confidentiality Impact

Integrity Impact

Availability Impact

Network

Low

None

None

None

Complete

CVSS Temporal Score - 6.4

Exploitability

Remediation Level

Report Confidence

Functional

Official-Fix

Confirmed

CSCsm67466 - Control-plane Access Control List Vulnerability

Calculate the environmental score of CSCsm67466

CVSS Base Score - 7.8

Access Vector

Access Complexity

Authentication

Confidentiality Impact

Integrity Impact

Availability Impact

Network

Low

None

Complete

None

None

CVSS Temporal Score - 6.4

Exploitability

Remediation Level

Report Confidence

Functional

Official-Fix

Confirmed

Impact

Successful exploitation of the first four vulnerabilities may cause a reload of the affected device. Repeated exploitation could result in a sustained Denial-of-Service (DoS) condition. Successful exploitation of the fifth vulnerability may allow an attacker to bypass control-plane ACLs and successfully send malicious traffic to the device.

Software Versions and Fixes

When considering software upgrades, also consult http://www.cisco.com/go/psirt and any subsequent advisories to determine exposure and a complete upgrade solution.

In all cases, customers should exercise caution to be certain the devices to be upgraded contain sufficient memory and that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, contact the Cisco Technical Assistance Center (TAC) or your contracted maintenance provider for assistance.

The following list contains the first fixed software release of each vulnerability:

Vulnerability

Affected Release

First Fixed Release

Crafted TCP ACK Packet Vulnerability

7.0

Not vulnerable

7.1

7.1(2)70

7.2

7.2(4)

8.0

8.0(3)10

8.1

Not vulnerable

Crafted TLS Packet Vulnerability

7.0

Not vulnerable

7.1

Not vulnerable

7.2

Not vulnerable

8.0

8.0(3)9

8.1

8.1(1)1

Instant Messenger Inspection Vulnerability

7.0

Not vulnerable

7.1

Not vulnerable

7.2

7.2(4)

8.0

8.0(3)10

8.1

8.1(1)2

Vulnerability Scan Denial of Service

7.0

Not vulnerable

7.1

Not vulnerable

7.2

7.2(3)2

8.0

8.0(2)17

8.1

Not vulnerable

Control-plane Access Control List Vulnerability

7.0

Not vulnerable

7.1

Not vulnerable

7.2

Not vulnerable

8.0

8.0(3)9

8.1

Not vulnerable

Fixed PIX software can be downloaded from:

http://www.cisco.com/pcgi-bin/tablebuild.pl/pix?psrtdcat20e2

Fix ASA software can be downloaded from:

http://www.cisco.com/pcgi-bin/tablebuild.pl/asa?psrtdcat20e2


Workarounds

This Security Advisory describes multiple distinct vulnerabilities. These vulnerabilities and their respective workarounds are independent of each other.

Crafted TCP ACK Packet Vulnerability

As a workaround and best practice allow Telnet, SSH, and ASDM connections from only trusted hosts in your network.

Additionally, filters that deny TCP ports 22, 23, 80, and 443 packets may be deployed throughout the network as part of a transit ACL (tACL) policy for protection of traffic which enters the network at ingress access points. This policy should be configured to protect the network device where the filter is applied and other devices behind it. Filters for packets using TCP ports 22, 23, 80, and 443 should also be deployed in front of vulnerable network devices so that traffic is only allowed from trusted clients.

Additional information about tACLs is available in "Transit Access Control Lists : Filtering at Your Edge":

http://www.cisco.com/en/US/tech/tk648/tk361/technologies_white_paper09186a00801afc76.shtml

Crafted TLS Packet Vulnerability

There are no workarounds for this vulnerability.

Instant Messenger Inspection Vulnerability

The only workaround for this vulnerability is to disable IM inspection on the security appliance.

Port Scan Denial of Service Vulnerability

There are no workarounds for this vulnerability.

Control-plane Access Control List Vulnerability

There are no workarounds for this vulnerability.

Additional mitigation techniques that can be deployed on Cisco devices within the network are available in the Cisco Applied Mitigation Bulletin companion document for this advisory:

http://tools.cisco.com/security/center/content/CiscoAppliedMitigationBulletin/cisco-amb-20080604-asa

Obtaining Fixed Software

Cisco has released free software updates that address these vulnerabilities. Prior to deploying software, customers should consult their maintenance provider or check the software for feature set compatibility and known issues specific to their environment.

Customers may only install and expect support for the feature sets they have purchased. By installing, downloading, accessing or otherwise using such software upgrades, customers agree to be bound by the terms of Cisco's software license terms found at http://www.cisco.com/en/US/docs/general/warranty/English/EU1KEN_.html, or as otherwise set forth at Cisco.com Downloads at http://www.cisco.com/public/sw-center/sw-usingswc.shtml.

Do not contact psirt@cisco.com or security-alert@cisco.com for software upgrades.

Customers with Service Contracts

Customers with contracts should obtain upgraded software through their regular update channels. For most customers, this means that upgrades should be obtained through the Software Center on Cisco's worldwide website at http://www.cisco.com.

Customers Using Third-Party Support Organizations

Customers whose Cisco products are provided or maintained through prior or existing agreements with third-party support organizations, such as Cisco Partners, authorized resellers, or service providers should contact that support organization for guidance and assistance with the appropriate course of action in regards to this advisory.

The effectiveness of any workaround or fix is dependent on specific customer situations, such as product mix, network topology, traffic behavior, and organizational mission. Due to the variety of affected products and releases, customers should consult with their service provider or support organization to ensure any applied workaround or fix is the most appropriate for use in the intended network before it is deployed.

Customers Without Service Contracts

Customers who purchase direct from Cisco but do not hold a Cisco service contract, and customers who purchase through third-party vendors but are unsuccessful in obtaining fixed software through their point of sale should acquire upgrades by contacting the Cisco Technical Assistance Center (TAC). TAC contacts are as follows.

  • +1 800 553 2447 (toll free from within North America)
  • +1 408 526 7209 (toll call from anywhere in the world)
  • e-mail: tac@cisco.com

Customers should have their product serial number available and be prepared to give the URL of this notice as evidence of entitlement to a free upgrade. Free upgrades for non-contract customers must be requested through the TAC.

Refer to http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml for additional TAC contact information, including localized telephone numbers, and instructions and e-mail addresses for use in various languages.

Exploitation and Public Announcements

The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerability described in this advisory.

These vulnerabilities were found during internal testing and during the troubleshooting of a technical support service request.

Status of This Notice: Final

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.

A stand-alone copy or Paraphrase of the text of this document that omits the distribution URL in the following section is an uncontrolled copy, and may lack important information or contain factual errors.


Distribution

This advisory is posted on Cisco's worldwide website at :

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080604-asa

In addition to worldwide web posting, a text version of this notice is clear-signed with the Cisco PSIRT PGP key and is posted to the following e-mail and Usenet news recipients.

  • cust-security-announce@cisco.com
  • first-teams@first.org
  • bugtraq@securityfocus.com
  • vulnwatch@vulnwatch.org
  • cisco@spot.colorado.edu
  • cisco-nsp@puck.nether.net
  • full-disclosure@lists.grok.org.uk
  • comp.dcom.sys.cisco@newsgate.cisco.com

Future updates of this advisory, if any, will be placed on Cisco's worldwide website, but may or may not be actively announced on mailing lists or newsgroups. Users concerned about this problem are encouraged to check the above URL for any updates.


Revision History

Revision 1.0

2008-June-04

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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