Cisco Security Advisory
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Two crafted packet vulnerabilities exist in the Cisco PIX 500 Series Security Appliance (PIX) and the Cisco 5500 Series Adaptive Security Appliance (ASA) that may result in a reload of the device. These vulnerabilities are triggered during processing of Media Gateway Control Protocol (MGCP) packets, or during processing of Transport Layer Security (TLS) traffic that terminates on the PIX or ASA security appliance.
Note: These vulnerabilities are independent of each other; a device may be affected by one and not by the other.
This advisory is posted at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20071017-asa.
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Vulnerable Products
The Cisco PIX and ASA security appliances are affected by a crafted MGCP packet vulnerability if MGCP application layer protocol inspection is enabled and the device is running certain 7.x software versions. Version 6.3.x is not affected. MGCP inspection is not enabled by default. For specific affected versions, refer to the Software Versions and Fixes section.
The PIX and ASA security appliances are also affected by a crafted TLS packet vulnerability that affects devices running certain 7.x software versions if the software has one or more features configured that cause TLS sessions to terminate on the PIX or ASA security appliance. These functions include, but are not limited to, clientless WebVPN, client connections with AnyConnect and the SSL VPN client, HTTPS management, cut-through proxy for network access, and TLS proxy for encrypted voice inspection. Version 6.3.x is not affected. Features that cause TLS sessions to terminate on the PIX and ASA security appliances are not enabled by default. For specific affected versions, please refer to the Software Versions and Fixes section.
In addition to the PIX and ASA security appliances, the crafted MGCP packet vulnerability also affects the Cisco Firewall Services Module (FWSM). More information regarding the FWSM can be found in the companion advisory https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20071017-fwsm.
To determine whether you are running a vulnerable version of Cisco PIX or ASA software, issue the show version command-line interface (CLI) command.
The following example shows a Cisco ASA Security Appliance that runs software release 7.2(3):
ASA# show version Cisco Adaptive Security Appliance Software Version 7.2(3) [...]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. The version notation is similar to this:
PIX Version 7.2(3)
Products Confirmed Not Vulnerable
With the exception of the FWSM, no other Cisco products are known to be vulnerable to the issues described in this advisory.
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This Security Advisory describes two distinct vulnerabilities that are independent of each other.
1. Crafted MGCP Packet
A PIX or ASA security appliance with the Media Gateway Control Protocol (MGCP) application layer protocol inspection feature enabled may reload when the device processes a crafted MGCP packet. MGCP application layer protocol inspection is not enabled by default.
MGCP messages are transmitted over the User Datagram Protocol (UDP), which does allow the crafted MGCP messages to be sourced from a spoofed address. Only the MGCP for gateway application (MGCP traffic on UDP port 2427) is affected.
To determine whether MGCP inspection is configured on the PIX or ASA, log in to the device and issue the CLI command show service-policy | include mgcp. If the output contains the text Inspect: mgcp 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 mgcp Inspect: mgcp, packet 15, drop 0, reset-drop 0 ASA#This vulnerability is documented in Cisco Bug ID CSCsi90468. The corresponding Cisco Bug ID for the FWSM, included in the companion FWSM Security Advisory, is CSCsi00694.
2. Crafted TLS Packet
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 PIX and 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.
The scenarios affected by this vulnerability are clientless WebVPN connections, HTTPS management sessions, cut-through proxy for network access, and TLS proxy for encrypted voice inspection.
Clientless WebVPN, SSL VPN Client, and AnyConnect Connections
Clientless WebVPN connections are enabled via the webvpn command. For example, the following configuration shows an ASA running 8.0 software with clientless 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.
HTTPS Management Sessions
HTTPS 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. A configuration that requires users to authenticate before they can be granted network access looks like the following example:
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 particular configuration in the preceding example, the device is vulnerable to attacks coming from the inside interface.
TLS Proxy for Encrypted Voice Inspection
This 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 Skinny 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, which implies that TLS sessions are terminating on the security appliance.
To determine whether the Cisco PIX or 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 IDs CSCsg43276 and CSCsh97120. This vulnerability does not affect the FWSM.
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Filters that deny TLS packets using TCP port 443 and MGCP packets on UDP port 2427 should 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 TLS packets using TCP port 443 and MGCP packets on UDP port 2427 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.
Additional mitigations techniques that can be deployed on Cisco devices within the network are available in the Cisco Applied Intelligence companion document for this advisory: http://www.cisco.com/warp/public/707/cisco-air-20071017-asafwsm.shtml.
1. Crafted MGCP Packet
There is no workaround for this vulnerability other than disabling MGCP application layer protocol inspection on the device.
Leveraging anti-spoofing techniques will help mitigate spoofed packets from triggering this vulnerability.
Limiting MGCP application layer inspection to traffic between MGCP gateways may help to mitigate this vulnerability since it would require an attacker to have additional information (the addresses of the MGCP gateways) to launch a successful attack. To limit MGCP application layer inspection to traffic between certain devices, a class map that matches only traffic between the gateways must be created. Then, MGCP inspection must be performed on traffic in that class. The following example shows how to accomplish this:
ASA(config)# access-list mgcp_traffic permit udp host 192.168.0.1 host 172.16.0.1 eq 2427 ASA(config)# access-list mgcp_traffic permit udp host 172.16.0.1 host 192.168.0.1 eq 2427 ASA(config)# class-map MGCP ASA(config-cmap)# match access-list mgcp_traffic ASA(config-cmap)# exit ASA(config)# policy-map global_policy ASA(config-pmap)# class inspection_default ASA(config-pmap-c)# no inspect mgcp ASA(config-pmap-c)# exit ASA(config-pmap)# class MGCP ASA(config-pmap-c)# inspect mgcp ASA(config-pmap-c)# exit ASA(config-pmap)# exit ASA(config)#
Note that MGCP inspection is applied only to UDP traffic between hosts 192.168.0.1 and 172.16.0.1
See the Cisco Applied Intelligence companion document for additional mitigation possibilities.
2. Crafted TLS Packet
ASDM is used to manage the Cisco PIX or ASA security appliance. Access to ASDM should be allowed only on trusted interfaces and only from authorized hosts. Restricting ASDM access to trusted hosts limits the ability of an attacker to conduct these attacks.
For example, to limit ASDM access to a single host on the inside interface with an address of 192.168.1.2, enter the following command:
hostname(config)# http 192.168.1.2 255.255.255.255 inside
Additional information is available at:
Cisco Security Appliance Command Line Configuration Guide, Version 7.2 ( http://www.cisco.com/en/US/docs/security/asa/asa72/configuration/guide/mgaccess.html#wp1047288)
There are no workarounds if the clientless WebVPN, client connections with AnyConnect and the SSL VPN client, cut-through proxy for network access, and TLS proxy for encrypted voice inspection features are in use.
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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 Major Release
First Fixed Release
Crafted MGCP packet.
7.0
7.0(6.33) or later
7.1
7.1(2.54) or later
7.2
7.2(2.23) or later
8.0
8.0(2)
Crafted TLS packet.
7.0
Not Affected
7.1
7.1(2.55) or later
7.2
7.2(2.24) or later
8.0
Not Affected
The following maintenance software releases are the first software releases that contain the fixes for the two vulnerabilities mentioned in this Security Advisory: 7.0(7), 7.1(3), 7.2(3), and 8.0(2).
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.
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The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerabilities described in this advisory.
These vulnerabilities were discovered by Cisco internal testing and customer service requests.
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To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.
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Revision 1.1
2007-October-19
Changed clientless WebVPN to include client connections with AnyConnect and the SSL VPN client.
Revision 1.0
2007-October-17
Initial public release.
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