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Category:   Device (Router/Bridge/Hub)  >   Cisco IOS Vendors:   Cisco
Cisco IOS Firewall Bug in HTTP Application Inspection Control Lets Remote Users Deny Service
SecurityTracker Alert ID:  1020929
SecurityTracker URL:
CVE Reference:   CVE-2008-3812   (Links to External Site)
Date:  Sep 24 2008
Impact:   Denial of service via network
Fix Available:  Yes  Vendor Confirmed:  Yes  

Description:   A vulnerability was reported in Cisco IOS in the firewall application inspection control function. A remote user can cause denial of service conditions.

A remote user can send a specially crafted HTTP packet through the target device to cause the target device to reload.

Systems configured for IOS firewall Application Inspection Control (AIC) with an HTTP configured application-specific policy are affected.

The vulnerable feature was introduced in release 12.4(9)T.

Cisco has assigned Cisco bug ID CSCsh12480 to this vulnerability.

Impact:   A remote user can cause the target device to reload.
Solution:   The vendor has issued a fix. A patch matrix is available in the vendor's advisory.

The vendor's advisory is available at:

Vendor URL: (Links to External Site)
Cause:   Input validation error

Message History:   None.

 Source Message Contents

Subject:  Cisco Security Advisory: Cisco IOS Software Firewall Application

Hash: SHA1

Cisco Security Advisory: Cisco IOS Software Firewall Application
Inspection Control Vulnerability

Advisory ID: cisco-sa-20080924-iosfw

Revision 1.0

For Public Release 2008 September 24 1600 UTC (GMT)

- ---------------------------------------------------------------------


Cisco IOS software configured for IOS firewall Application Inspection
Control (AIC) with a HTTP configured application-specific policy are
vulnerable to a Denial of Service when processing a specific
malformed HTTP transit packet. Successful exploitation of the
vulnerability may result in a reload of the affected device.

Cisco has released free software updates that address this

A mitigation for this vulnerability is available. See the
"Workarounds" section for details.

This advisory is posted at

Note: The September 24, 2008 IOS Advisory bundled publication
includes twelve Security Advisories. Eleven of the advisories address
vulnerabilities in Cisco's IOS software, and one advisory addresses
vulnerabilities in Cisco Unified Communications Manager. Each
Advisory lists the releases that correct the vulnerability described
in the Advisory. Please reference the following software table to
find a release that fixes all published IOS software Advisories as of
September 24th, 2008:

Individual publication links are listed below:


Affected Products

The HTTP AIC feature was introduced in Cisco IOS Software Release
12.4(9)T. The software table in this advisory identifies the affected

Vulnerable Products

Devices that are running a vulnerable version of Cisco IOS software
and configured for Cisco IOS firewall AIC for HTTP are affected.

To determine the software running on a Cisco IOS product, log in to
the device and issue the show version command-line interface (CLI)
command to display the system banner. Cisco IOS software will
identify itself as "Internetwork Operating System Software" or simply
"IOS." On the next line of output, the image name will be displayed
between parentheses, followed by "Version" and the Cisco IOS release
name. Other Cisco devices will not have the show version command, or
will give different output.

The following example shows output from a device running Cisco IOS
image 12.4(15)T2:

    router#show version
    Cisco IOS Software, 1841 Software (C1841-ADVSECURITYK9-M),
       Version 12.4(15)T2, RELEASE SOFTWARE (fc7) Technical Support: Copyright (c) 1986-2008 by Cisco
    Systems, Inc. Compiled Thu 17-Jan-08 23:12 by prod_rel_team

    !--- Output truncated.

Additional information on the Cisco IOS release naming conventions
can be found on the document entitled "White Paper: Cisco IOS
Reference Guide", which is available at

The device is vulnerable if the configuration has a Layer 7 class map
and Layer 7 policy map for HTTP deep packet inspection (DPI), and
these policies are applied to any firewall zone. To determine whether
the device is running a vulnerable configuration of Cisco IOS
firewall AIC for HTTP, log in to the device and issue the CLI command
show policy-map type inspect zone-pair | section packet inspection.
If the output contains Policy: http layer7-policymap name , the
device is vulnerable. The following example shows the response from a
vulnerable device:

    Router#show policy-map type inspect zone-pair | section packet inspection

             Deep packet inspection
                Policy: http layer7-policymap
                1 packets, 28 bytes


Products Confirmed Not Vulnerable

No other Cisco products are currently known to be affected by this
vulnerability. IOS releases before 12.4(9)T are not affected by this
issue. Products confirmed not vulnerable include:

  * Cisco PIX
  * Cisco ASA
  * Cisco Firewall Services Module (FWSM)
  * The Virtual Firewall (VFW) application on the multiservice blade
    (MSB) on the Cisco XR 12000 Series Router


Firewalls are networking devices that control access to an
organization's network assets. Firewalls are often positioned at the
entrance points into networks. Cisco IOS software provides a set of
security features that enable you to configure a simple or elaborate
firewall policy, according to your particular requirements.

HTTP uses port 80 by default to transport Internet web services,
which are commonly used on the network and rarely challenged with
regard to their legitimacy and conformance to standards. Because port
80 traffic is typically allowed through the network without being
challenged, many application developers are leveraging HTTP traffic
as an alternative transport protocol that will allow their
application's traffic to travel through or even bypass the firewall.
When the Cisco IOS Firewall is configured with HTTP AIC, it performs
packet inspection to detect HTTP connections that are not authorized
in the scope of the security policy configuration. It also detects
users who are tunneling applications through port 80. If the packet
is not in compliance with the HTTP protocol, it will be dropped, the
connection will be reset, and a syslog message will be generated, as

Cisco IOS Software that is configured for IOS firewall AIC with an
HTTP application-specific policy is vulnerable to a denial of service
condition when it processes a specific malformed HTTP transit packet.
Successful exploitation of the vulnerability may result in a reload
of the affected device.

HTTP runs over TCP. For this vulnerability to be exploited, a full
three-way handshake between client and server is required before any
malicious traffic would be processed to result in a device reload.

Additional information regarding Cisco IOS Firewall AIC with HTTP
application-specific policy maps is available at

This vulnerability is documented in Cisco bug ID CSCsh12480 
and Common Vulnerabilities and Exposures (CVE) identifier 
CVE-2008-3812 has been assigned to this vulnerability.

Vulnerability Scoring Details

Cisco has provided scores for the vulnerability 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

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

CSCsh12480 - IOSFW with HTTP AIC may reload on processing crafted
             HTTP packet

CVSS Base Score - 7.8

        Access Vector          - Network
        Access Complexity      - Low
        Authentication         - None
        Confidentiality Impact - None
        Integrity Impact       - None
        Availability Impact    - Complete

CVSS Temporal Score - 6.4

        Exploitability          - Functional
        Remediation Level       - Official-Fix
        Report Confidence       - Confirmed


Successful exploitation of the vulnerability may result in a reload
of the affected device. Repeated exploitation attempts may result in
a sustained denial of service attack.

Software Versions and Fixes

When considering software upgrades, also consult 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.

Each row of the Cisco IOS software table (below) names a Cisco IOS
release train. If a given release train is vulnerable, then the
earliest possible releases that contain the fix (along with the
anticipated date of availability for each, if applicable) are listed
in the "First Fixed Release" column of the table. The "Recommended
Release" column indicates the releases which have fixes for all the
published vulnerabilities at the time of this Advisory. A device
running a release in the given train that is earlier than the release
in a specific column (less than the First Fixed Release) is known to
be vulnerable. Cisco recommends upgrading to a release equal to or
later than the release in the "Recommended Releases" column of the

|  Major Release  |        Availability of Repaired Releases        |
|    Affected     |                                   | Recommended |
|   12.0-Based    |        First Fixed Release        |   Release   |
|    Releases     |                                   |             |
| There are no affected 12.0 based releases                         |
|    Affected     |                                   | Recommended |
|   12.1-Based    |        First Fixed Release        |   Release   |
|    Releases     |                                   |             |
| There are no affected 12.1 based releases                         |
|    Affected     |                                   | Recommended |
|   12.2-Based    |        First Fixed Release        |   Release   |
|    Releases     |                                   |             |
| There are no affected 12.2 based releases                         |
|    Affected     |                                   | Recommended |
|   12.3-Based    |        First Fixed Release        |   Release   |
|    Releases     |                                   |             |
| There are no affected 12.3 based releases                         |
|    Affected     |                                   | Recommended |
|   12.4-Based    |        First Fixed Release        |   Release   |
|    Releases     |                                   |             |
| 12.4            | Not Vulnerable                    |             |
| 12.4JA          | Not Vulnerable                    |             |
| 12.4JK          | Not Vulnerable                    |             |
| 12.4JL          | Not Vulnerable                    |             |
| 12.4JMA         | Not Vulnerable                    |             |
| 12.4JMB         | Not Vulnerable                    |             |
| 12.4JMC         | Not Vulnerable                    |             |
| 12.4JX          | Not Vulnerable                    |             |
| 12.4MD          | Not Vulnerable                    |             |
| 12.4MR          | Not Vulnerable                    |             |
| 12.4SW          | Not Vulnerable                    |             |
|                 | Releases prior to 12.4(9)T are    |             |
|                 | not vulnerable. First fixed in:   |             |
|                 |                                   |             |
| 12.4T           | 12.4(9)T7                         | 12.4(15)T7  |
|                 |                                   |             |
|                 | 12.4(11)T4                        |             |
|                 |                                   |             |
|                 | 12.4(15)T                         |             |
| 12.4XA          | Not Vulnerable                    |             |
| 12.4XB          | Not Vulnerable                    |             |
| 12.4XC          | Not Vulnerable                    |             |
| 12.4XD          | Not Vulnerable                    |             |
| 12.4XE          | Vulnerable; first fixed in 12.4T  | 12.4(15)T7  |
| 12.4XF          | Not Vulnerable                    |             |
| 12.4XG          | Not Vulnerable                    |             |
| 12.4XJ          | Vulnerable; first fixed in 12.4T  | 12.4(15)T7  |
| 12.4XK          | Vulnerable; first fixed in 12.4T  | 12.4(15)T7  |
| 12.4XL          | Not Vulnerable                    |             |
| 12.4XM          | Not Vulnerable                    |             |
| 12.4XN          | Not Vulnerable                    |             |
| 12.4XP          | Not Vulnerable                    |             |
| 12.4XQ          | Not Vulnerable                    |             |
| 12.4XT          | Not Vulnerable                    |             |
| 12.4XV          | Vulnerable; contact TAC           |             |
| 12.4XW          | 12.4(11)XW1                       | 12.4(11)XW9 |
| 12.4XY          | Not Vulnerable                    |             |
| 12.4XZ          | Not Vulnerable                    |             |
| 12.4YA          | Not Vulnerable                    |             |


There are no known workarounds for this vulnerability. The only known
action to help counter this vulnerability is to disable AIC HTTP deep
packet inspection in the affected device's configuration. Disabling
deep packet HTTP inspection will allow the rest of the firewall
features to continue to function until a software upgrade can be
implemented. All other firewall features will continue to perform

Disabling AIC HTTP Deep Packet Inspection

To disable AIC HTTP Deep Packet Inspection, remove the linkage
between policy-map type inspect layer4-policymap and policy-map type
inspect http layer7-policymap. This example shows an existing
configuration, followed by how to remove AIC HTTP Deep Packet

    !--- Existing Configuration

    parameter-map type inspect global


    class-map type inspect http match-any layer7-classmap
    class-map type inspect match-any layer4-classmap
     match protocol http


    policy-map type inspect http layer7-policymap
     class type inspect http layer7-classmap
     class class-default
    policy-map type inspect layer4-policymap
     class type inspect layer4-classmap
      inspect global
      service-policy http layer7-policymap
     class class-default


    zone security inside
     description ** Inside Network **
    zone security outside
     description ** Outside Network **
    zone-pair security in2out source inside destination outside
     description ** Zone Pair - inside to outside **
     service-policy type inspect layer4-policymap

Remove the service-policy from the zone-pair in question:

    Router#configure terminal
    Enter configuration commands, one per line.  End with CNTL/Z.
    Router(config)#zone-pair security in2out source inside destination outside
    Router(config-sec-zone-pair)#no service-policy type inspect layer4-policymap

Remove the linkage between policy-map type inspect layer4-policymap
and policy-map type inspect http layer7-policymap:

    Router(config)#policy-map type inspect layer4-policymap
    Router(config-pmap)#class type inspect layer4-classmap
    Router(config-pmap-c)#no service-policy http layer7-policymap

Reapply the service-policy to the zone-pair in question:

    Router(config)#zone-pair security in2out source inside destination outside
    Router(config-sec-zone-pair)#service-policy type inspect layer4-policymap

Although not required, for completeness of the configuration the
policy-map type inspect http layer7-policymap and class-map type
inspect http match-any layer7-classmap are recommended to be removed.

    Router(config)#no policy-map type inspect http layer7-policymap
    Router(config)#no class-map type inspect http match-any layer7-classmap

Obtaining Fixed Software

Cisco has released free software updates that address this
vulnerability. 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
or as otherwise set forth at Downloads at

Do not contact or 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

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:

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
for additional TAC contact information, including localized telephone
numbers, and instructions and e-mail addresses for use in various

Exploitation and Public Announcements

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

This vulnerability was found by Cisco internal testing.

Status of this Notice: FINAL


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.


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

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.


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 |                   | Initial |
| 1.0      | 2008-September-24 | 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
This includes instructions for press inquiries regarding Cisco 
security notices. All Cisco security advisories are available at
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