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             AUSCERT External Security Bulletin Redistribution

                              ESB-2023.4377.3
  Cisco Secure Web Appliance Content Encoding Filter Bypass Vulnerability
                             20 November 2023

===========================================================================

        AusCERT Security Bulletin Summary
        ---------------------------------

Product:           Cisco Secure Web Appliance
Publisher:         Cisco Systems
Operating System:  Cisco
Resolution:        Patch/Upgrade
CVE Names:         CVE-2023-20215  

Original Bulletin: 
   https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-wsa-bypass-vXvqwzsj

Comment: CVSS (Max):  5.8 CVE-2023-20215 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N)
         CVSS Source: Cisco Systems
         Calculator:  https://www.first.org/cvss/calculator/3.1#CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N

Revision History:  November 20 2023: Added CVSS information in the mail subject
                   November 20 2023: Updated release-specific default configuration and mitigation information
                   August    3 2023: Initial Release

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Cisco Secure Web Appliance Content Encoding Filter Bypass Vulnerability

Priority:        Medium
Advisory ID:     cisco-sa-wsa-bypass-vXvqwzsj
First Published: 2023 August 2 16:00 GMT
Last Updated:    2023 November 17 21:04 GMT
Version 1.2:     Interim
Workarounds:     No workarounds available
Cisco Bug IDs:   CSCwf55917 CSCwf60901 CSCwf94501
CVE Names:       CVE-2023-20215

Summary

  o A vulnerability in the scanning engines of Cisco AsyncOS Software for Cisco
    Secure Web Appliance could allow an unauthenticated, remote attacker to
    bypass a configured rule, allowing traffic onto a network that should have
    been blocked.

    This vulnerability is due to improper detection of malicious traffic when
    the traffic is encoded with a specific content format. An attacker could
    exploit this vulnerability by using an affected device to connect to a
    malicious server and receiving crafted HTTP responses. A successful exploit
    could allow the attacker to bypass an explicit block rule and receive
    traffic that should have been rejected by the device.

    There are no workarounds that address this vulnerability.

    This advisory is available at the following link:
    https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-wsa-bypass-vXvqwzsj

Affected Products

  o Vulnerable Products

    At the time of publication, this vulnerability affected Cisco Secure Web
    Appliance, both virtual and hardware versions, when the deflate , lzma , or
    brotli content-encoding type was enabled.

    Note: For Cisco Secure Web Appliance Releases 14.5.1 and earlier, the
    deflate content-encoding type is disabled by default, but the lzma and
    brotli content-encoding types are enabled by default. For Cisco Secure Web
    Appliance Releases 14.5.2 and later, the deflate, lzma , and brotli 
    content-encoding types are disabled by default.

    Determine the Content-Encoding Type

    To determine whether the deflate , lzma , or brotli content-encoding type
    is enabled on Cisco Secure Web Appliance, run the advancedproxyconfig 
    command followed by the CONTENT-ENCODING command as an administrator in the
    CLI. If the CONTENT-ENCODING command returns deflate , lzma , or br under
    Currently allowed content-encoding type(s) , that content-encoding type is
    enabled, as shown in the following example:

        cisco-wsa> advancedproxyconfig
        cisco-wsa> CONTENT-ENCODING

        Enter values for the CONTENT-ENCODING options:
        Currently allowed content-encoding type(s): deflate, lzma, br

    For information about which Cisco software releases were vulnerable at the
    time of publication, see the Fixed Software section of this advisory. See
    the Details section in the bug ID(s) at the top of this advisory for the
    most complete and current information.

    Products Confirmed Not Vulnerable

    Only products listed in the Vulnerable Products section of this advisory
    are known to be affected by this vulnerability.

    Cisco has confirmed that this vulnerability does not affect the following
    Cisco products:

       Secure Email Gateway, formerly Email Security Appliance (ESA), both
        virtual and hardware appliances
       Secure Email and Web Manager, both virtual and hardware appliances

    Attention: Simplifying the Cisco portfolio includes the renaming of
    security products under one brand: Cisco Secure. For more information, see
    Meet Cisco Secure .

Workarounds

  o There are no workarounds that address this vulnerability. However,
    administrators can mitigate this vulnerability in one of two ways:

       Disable the deflate , lzma , and brotli content-encoding types if they
        are not required.
       Migrate to Cisco Secure Web Appliance Release 14.5.2, in which deflate 
        , lzma , and brotli content-encoding types are disabled by default.

    Disable the Content-Encoding Type

    To disable a specific content-encoding type, use the following steps:

     1. Log in to the admin console interface for the device.
     2. Choose advancedproxyconfig > CONTENT-ENCODING .
     3. Enter the number associated with the specific content-encoding type.
     4. If the following message is displayed, enter Y at the prompt:

            The encoding type <"content-encoding type"> is currently allowed
            Do you want to block it [N]> Y

        If the following message is displayed, enter N at the prompt:

            The encoding type <"content-encoding type"> is currently blocked
            Do you want to allow it [N]> N

     5. Run the Commit command.

    While this mitigation has been deployed and was proven successful in a test
    environment, customers should determine the applicability and effectiveness
    in their own environment and under their own use conditions. Customers
    should be aware that any workaround or mitigation that is implemented may
    negatively impact the functionality or performance of their network based
    on intrinsic customer deployment scenarios and limitations. Customers
    should not deploy any workarounds or mitigations before first evaluating
    the applicability to their own environment and any impact to such
    environment.

Fixed Software

  o When considering software upgrades , customers are advised to regularly
    consult the advisories for Cisco products, which are available from the
    Cisco Security Advisories page , 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.

    Fixed Releases

    At the time of publication, the release information in the following table
    (s) was accurate. See the Details section in the bug ID(s) at the top of
    this advisory for the most complete and current information.

    The left column lists Cisco software releases, and the right column
    indicates whether a release was affected by the vulnerability that is
    described in this advisory and which release included the fix for this
    vulnerability.

    Cisco AsyncOS for Secure Web Appliance Software First Fixed Release
    Release
    14.0 and earlier                                Migrate to a fixed release.
    14.5                                            Release no. TBD (future
                                                    release)

    The Cisco Product Security Incident Response Team (PSIRT) validates only
    the affected and fixed release information that is documented in this
    advisory.

Exploitation and Public Announcements

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

Source

  o Cisco would like to thank q.beyond AG for reporting this vulnerability.

Cisco Security Vulnerability Policy

  o 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.

Subscribe to Cisco Security Notifications

  o Subscribe

URL

  o https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-wsa-bypass-vXvqwzsj

Revision History

  o +---------+-------------------------+-------------+---------+-------------+
    | Version |       Description       |   Section   | Status  |    Date     |
    +---------+-------------------------+-------------+---------+-------------+
    |         | Updated                 |             |         |             |
    |         | release-specific        | Vulnerable  |         |             |
    | 1.2     | default configuration   | products,   | Interim | 2023-NOV-17 |
    |         | and mitigation          | Workarounds |         |             |
    |         | information.            |             |         |             |
    +---------+-------------------------+-------------+---------+-------------+
    | 1.1     | Updated source          | Source      | Interim | 2023-AUG-03 |
    |         | information.            |             |         |             |
    +---------+-------------------------+-------------+---------+-------------+
    | 1.0     | Initial public release. | -           | Interim | 2023-AUG-02 |
    +---------+-------------------------+-------------+---------+-------------+

Legal Disclaimer

  o 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. CISCO EXPECTS TO
    UPDATE THIS DOCUMENT AS NEW INFORMATION BECOMES AVAILABLE.

    A standalone copy or paraphrase of the text of this document that omits the
    distribution URL is an uncontrolled copy and may lack important information
    or contain factual errors. The information in this document is intended for
    end users of Cisco products.

- --------------------------END INCLUDED TEXT--------------------

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