Cisco Web Security Appliance Range Request Denial of Service Vulnerability

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Updated:November 4, 2015
Document ID:1454773575872738

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Cisco Security Advisory

Cisco Web Security Appliance Range Request Denial of Service Vulnerability

High
Advisory ID:
cisco-sa-20151104-wsa2
First Published:
2015 November 4 16:00 GMT
Last Updated: 
2015 November 20 17:48 GMT
Version 1.1:
Final
Workarounds:
Yes
Cisco Bug IDs:
CSCur39155
CSCuu29304
CVE-2015-6293
CWE-399
CVSS Score:
Base 7.8, Temporal 6.4Click Icon to Copy Verbose Score
AV:N/AC:L/Au:N/C:N/I:N/A:C/E:F/RL:OF/RC:C
CVE-2015-6293
CWE-399

Summary

  • A vulnerability in the file-range request functionality of Cisco AsyncOS for Cisco Web Security Appliance (WSA) could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an appliance because the appliance runs out of system memory.

    The vulnerability is due to a failure to free memory when a file range is requested through the Cisco WSA. An attacker could exploit this vulnerability by opening multiple connections that request file ranges through the WSA. A successful exploit could allow the attacker to cause the WSA to stop passing traffic when enough memory is used and not freed.

    Cisco has released software updates that address this vulnerability. A workaround that mitigates this vulnerability is also available.

    This advisory is available at the following link:

     http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20151104-wsa2

Affected Products

  • Vulnerable Products

    This vulnerability affects Cisco AsyncOS versions 8.0 through 8.8 for Cisco WSA on both virtual and hardware appliances.

    To determine whether a vulnerable version of Cisco AsyncOS Software is running on a Cisco WSA, administrators can use the version command in the WSA CLI. The following example shows the results for an appliance running Cisco AsyncOS Software version 8.5.3-051:

    ciscowsa> version
    Current Version
    ===============
    Product: Cisco IronPort S670 Web Security Appliance
    Model: S670
    Version: 8.5.3-051
.
.
.

    See the "Fixed Software" section of this security advisory for more information about the affected versions.

    Products Confirmed Not Vulnerable

    The following products are not affected by this vulnerability:
    • Cisco Email Security Appliance (ESA), both virtual and hardware versions
    • Cisco Security Mail Appliance (SMA), both virtual and hardware versions

    No other Cisco products are currently known to be affected by this vulnerability.

Indicators of Compromise

  • The indicator of compromise for this vulnerability is an accumulation of TCP connections that are not freed, which can lead to memory exhaustion. To determine whether there is an accumulation of connections, use the status detail command in the Cisco WSA CLI. The value of the Total client connections field may show a large number of connections, as shown in the following example:
    # status detail
Connections:
  Total client connections                   99999

    If this condition is observed, the appliance may have been compromised by this vulnerability. In addition, any indication of memory exhaustion should be examined because this vulnerability is a memory leak.

Workarounds

  • If the results of using the status detail command in the Cisco WSA CLI indicate an accumulation of TCP connections, as described in the "Indicators of Compromise" section, use the hidden diagnostic -> PROXY -> KICK command to restart the proxy process and reclaim memory.

Fixed Software

  • When considering software upgrades, customers are advised to consult the Cisco Security Advisories and Responses 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 upgrade 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.

    In the following table, the left column lists major releases of Cisco AsyncOS Software for Cisco WSA. The center column indicates whether a major release is affected by the vulnerability described in this advisory and the first minor release that includes the fix for this vulnerability. The right column indicates whether a major release is affected by all the vulnerabilities described in this and the following companion advisories and which release includes fixes for those vulnerabilities:

    Customers should upgrade to an appropriate release as indicated in the following table:

    AsyncOS for WSA
    Major Release         		First Fixed Release for
    This Vulnerability         		First Fixed Release for
    This Vulnerability and
    All Vulnerabilities Described in the
    Companion Advisories
    7.5 and prior
    		 Not affected 7.7.0-761 or later
    7.7
    		 Not affected
    		 7.7.0-761 or later
    8.0 8.0.8-113 8.0.8-113 or later
    8.1 Affected; migrate to 8.5.3-051 Affected; migrate to 8.5.3-051 or later
    8.5 8.5.3-051 8.5.3-051 or later
    8.6 Affected; migrate to 8.7.0-171-LD Affected; migrate to 8.7.0-171-LD or later
    8.7 8.7.0-171-LD 8.7.0-171-LD or later
    8.8 8.8.0-085 8.8.0-085 or later
    9.0 Not affected Not affected

    In most cases a WSA can be updated over the network by using the System Upgrade options in the System Administration GUI. To upgrade a device by using the System Administration GUI:

    1. Choose System Administration > System Upgrade.
    2. Click Upgrade Options.
    3. Choose the option to Download and Install or, for an ESA, Download the upgrade.
    4. Choose the release to upgrade to.
    5. In the Upgrade Preparation area, choose the appropriate options.
    6. Click Proceed to begin the upgrade. A progress bar displays the status of the upgrade.

    After the upgrade is complete, the device reboots.

Exploitation and Public Announcements

  • 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.

Source

  • This vulnerability was found during the resolution of a support case.

Cisco Security Vulnerability Policy

  • 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 History

  • Version Description Section Status Date
    1.1 Added steps for upgrading a device by using the GUI. Fixed Software Final 2015-November-20
    1.0 Initial public release. — Final 2015-November-04
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Cisco Security Vulnerability Policy

  • 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