Advisory ID: cisco-sa-20130626-ngfw
For Public Release 2013 June 26 16:00 UTC (GMT)
Cisco ASA Next-Generation Firewall (NGFW) Services contains a Fragmented Traffic Denial of Service (DoS) vulnerability.
Successful exploitation of this vulnerability on the Cisco ASA NGFW could cause the device to reload or stop processing user traffic that has been redirected by the parent Cisco ASA to the ASA NGFW module for further inspection.
There are no workarounds for this vulnerability, but mitigations are available.
Cisco has released free software updates that address this vulnerability. This advisory is available at the following link:
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 184.108.40.206
9.1.2 versions of Cisco NGFW prior to 220.127.116.11
All 9.0 versions of Cisco NGFW
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
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.
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.
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
customers only) for Cisco ASA Next-Generation Firewall Services and has been assigned Common Vulnerabilities and Exposures (CVE) ID CVE-2013-3382.
Cisco has scored the vulnerability in this advisory based on the Common Vulnerability Scoring System (CVSS). The CVSS scoring in this security advisory is in accordance with CVSS version 2.0.
CVSS is a standards-based scoring method that conveys vulnerability severity and helps organizations determine the urgency and priority of a response.
Cisco has provided a base and temporal score. Customers can also compute environmental scores that help determine the impact of the vulnerability in their own networks.
Cisco has provided additional information regarding CVSS at the following link:
Cisco has also provided a CVSS calculator to compute the environmental impact for individual networks at the following link:
CSCue88387 -- Cisco ASA Next-Generation Firewall Fragmented Traffic Denial of Service Vulnerability
Calculate the environmental score of CSCue88387
CVSS Base Score - 7.8
CVSS Temporal Score - 6.8
Successful exploitation of the vulnerability on the Cisco ASA NGFW appliance may cause the device to reload or stop processing user traffic.
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.
Repeated exploitation could result in a sustained failover condition of the parent Cisco ASA, and eventually lead to a sustained DoS condition.
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 18.104.22.168 or 22.214.171.124 and later.
Cisco ASA NGFW Software can be downloaded at the following link:
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
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.
Cisco has released free software updates that address the vulnerability described in this advisory. Prior to deploying software, customers are advised to consult their maintenance providers or check the software for feature set compatibility and known issues that are specific to their environments.
Customers may only install and expect support for feature sets they have purchased. By installing, downloading, accessing, or otherwise using such software upgrades, customers agree to follow the terms of the Cisco software license at http://www.cisco.com/en/US/docs/general/warranty/English/EU1KEN_.html.
Customers with Cisco products that 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 organization for assistance with the appropriate course of action.
The effectiveness of any workaround or fix depends on specific customer situations, such as product mix, network topology, traffic behavior, and organizational mission. Because of the variety of affected products and releases, customers should consult their service providers or support organizations to ensure that any applied workaround or fix is the most appropriate in the intended network before it is deployed.
Customers who purchase directly from Cisco but do not hold a Cisco service contract and customers who make purchases through third-party vendors but are unsuccessful in obtaining fixed software through their point of sale should obtain upgrades by contacting the Cisco Technical Assistance Center (TAC):
- +1 800 553 2447 (toll free from within North America)
- +1 408 526 7209 (toll call from anywhere in the world)
- e-mail: email@example.com
Customers should have the product serial number available and be prepared to provide the URL of this advisory as evidence of entitlement to a free upgrade. Customers without service contracts should request free upgrades through the TAC.
Refer to Cisco Worldwide Contacts at http://www.cisco.com/en/US/support/tsd_cisco_worldwide_contacts.html for additional TAC contact information, including localized telephone numbers, instructions, and e-mail addresses for support in various languages.
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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Additionally, a text version of this advisory is clear signed with the Cisco PSIRT PGP key and circulated among the following e-mail addresses:
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||Initial public release