Cisco Security Advisory
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AV:N/AC:L/Au:N/C:N/I:N/A:C/E:H/RL:OF/RC:C
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Cisco ASA Next-Generation Firewall (NGFW) Services contains a Fragmented Traffic Denial of Service (DoS) vulnerability.
There are no workarounds for this vulnerability, but mitigations are available.
Cisco has released software updates that address this vulnerability. This advisory is available at the following link:
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20130626-ngfw
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Vulnerable Products
The following versions of Cisco ASA NGFW are affected by the vulnerability in this advisory:
9.1.1 versions of Cisco ASA NGFW prior to 9.1.1.9
9.1.2 versions of Cisco NGFW prior to 9.1.2.12
All 9.0 versions of Cisco NGFW
Note: Both Cisco ASA NGFW hardware and software modules for Cisco ASA are affected by this vulnerability.
Determining Cisco ASA Next-Generation Firewall Services Software Versions
Cisco ASA NGFW is known as Cisco ASA CX Context-Aware Security in versions prior to 9.1.2.
To determine the running version of Cisco ASA NGFW software, issue the show version command from the Cisco ASA NGFW command line interface, to which an administrator can get access via serial console, an SSH session to the ASA NGFW management interface, or a session opened from the parent ASA using the session command.
The following example shows Cisco ASA NGFW software Version 9.0.1(40):
asangfw> show version Cisco ASA CX Platform 9.0.1 (40)Customers using Cisco Prime Security Manager (PRSM )to manage Cisco ASA NGFW devices can locate the software version of Cisco ASA NGFW in the Device > Devices part of the Cisco Prime Security Manager window.
Products Confirmed Not Vulnerable
Cisco ASA 5500 Series Adaptive Security Appliances, Cisco Catalyst 6500 or 7600 Series ASA Services Module (ASA-SM), and Cisco Catalyst 6500 Series Firewall Services Module (FWSM) are not affected by this vulnerability.
Cisco PRSM is not affected by this vulnerability.
No other Cisco products are currently known to be affected by this vulnerability.
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The Cisco ASA NGFW is an add-on services module that extends the Cisco ASA platform by delivering application and user ID awareness capabilities for enhanced visibility and control of network traffic.
A vulnerability in fragmented traffic processing on Cisco ASA NGFW could allow an unauthenticated, remote attacker to cause a reload of the affected device.
The vulnerability is due to invalid parsing of reassembled packet data. An attacker could exploit this vulnerability by sending fragmented traffic to be processed by one of the ASA NGFW deny policies.
Under specific conditions, an attacker could exploit this vulnerability by sending fragmented IPv4 or IPv6 packets through the Cisco ASA NGFW. To exploit this vulnerability, an affected Cisco ASA NGFW must have a configured policy that denies user traffic. Processing fragmented packets against a deny policy, could cause the Cisco ASA NGFW to reload.
Additionally, if the Cisco ASA, with a Cisco ASA NGFW module running an affected version of software is configured in High-Availability mode (HA), a failover event may be triggered when the Cisco ASA NGFW reloads or stops forwarding traffic.
Only user traffic specifically directed towards the Cisco ASA NGFW by the Modular Policy Framework (MPF) configuration on the parent Cisco ASA is affected by the vulnerability in this advisory.
Management traffic to or from Cisco ASA NGFW is not affected by this vulnerability.
This vulnerability is documented in Cisco bug ID CSCue88387 (registered customers only) for Cisco ASA Next-Generation Firewall Services and has been assigned Common Vulnerabilities and Exposures (CVE) ID CVE-2013-3382.
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If the vulnerability has been exploited on the Cisco ASA NGFW and the traffic is interrupted, as a mitigation, the Modular Policy Framework (MPF) configuration on the Cisco ASA that is used to direct the user traffic toward the Cisco ASA NGFW can be removed. This will cause all user traffic to bypass Cisco ASA NGFW module inspection and allow it to pass through the Cisco ASA without inspection provided by the ASA NGFW.
The following example shows how to disable the redirecting of web traffic to the Cisco ASA NGFW module from the Cisco ASA firewall:
ASA(config)# policy-map cx_traffic_policy
ASA(config-pmap)# class cx_traffic
ASA(config-pmap-c)# no cxcs
Note: Cisco ASA can be configured with fail-open under MPF configuration. The fail-open keyword sets the Cisco ASA to allow all traffic through, uninspected, if the Cisco ASA NGFW module is unavailable.
Alternatively, fragmented traffic can be disallowed on the Cisco ASA firewall. This will cause the Cisco ASA firewall not to accept any fragments on its interfaces. Consequently, the Cisco ASA will not send any fragments to the Cisco ASA NGFW software module for inspection.
The following example shows how to disable processing of fragmented traffic on the Cisco ASA firewall:ASA(config)# fragment chain 1
Note: The above example will disable fragments on all the Cisco ASA interfaces. Fragmented traffic directed to and through the Cisco ASA will be dropped. Consequently, the Cisco ASA will not forward any fragmented traffic to the Cisco ASA NGFW or any of the configured modules.
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When considering software upgrades, customers are advised to consult the Cisco Security Advisories, Responses, and Notices archive at http://www.cisco.com/go/psirt and review subsequent advisories to determine exposure and a complete upgrade solution.
In all cases, customers should ensure that the devices to be upgraded contain sufficient memory and confirm that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, customers are advised to contact the Cisco Technical Assistance Center (TAC) or their contracted maintenance providers.
This vulnerability has been fixed in Cisco ASA NGFW versions 9.1.1.9 or 9.1.2.12 and later.
Cisco ASA NGFW Software can be downloaded at the following link:
http://software.cisco.com/download/release.html?mdfid=284325223&softwareid=284399944&release=9.1.1-17&relind=AVAILABLE&rellifecycle=&reltype=latest
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The Cisco Product Security Incident Response Team (PSIRT) is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.
This vulnerability was discovered during resolution of a support case.
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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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Show LessRevision 1.0 2013-June-26 Initial public release
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