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Cisco Security Advisory

Cisco AsyncOS TCP Flood Denial of Service Vulnerability

High
Advisory ID:
cisco-sa-20151104-aos
First Published:
2015 November 4 16:00 GMT
Last Updated:
2015 November 20 17:48 GMT
Version 1.3:
Final
Workarounds:
No workarounds available
CVE-2015-6321
CWE-399
CVSS Score:
Base 7.1, Temporal 5.9Click Icon to Copy Verbose Score
AV:N/AC:M/Au:N/C:N/I:N/A:C/E:F/RL:OF/RC:C
CVE-2015-6321
CWE-399

Summary

  • A vulnerability in the network stack of Cisco AsyncOS for Cisco Email Security Appliance (ESA), Cisco Content Security Management Appliance (SMA) and Cisco Web Security Appliance (WSA) could allow an unauthenticated, remote attacker to exhaust all available memory, preventing the affected device from accepting new TCP connections.

    The vulnerability is due to improper handling of TCP packets sent at a high rate. An attacker could exploit this vulnerability by sending crafted TCP packets to the affected system.

    Note: A full device reload is needed to recover the system to an operational state.

    Cisco has released software updates that address this vulnerability. There are no workarounds that mitigate this vulnerability. This advisory is available at the following link:
    https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20151104-aos

Affected Products

  • Vulnerable Products

    This vulnerability affects the following products running a vulnerable version of the Cisco AsyncOS Software:
    • Cisco Email Security Appliance (ESA), both virtual and hardware versions
    • Cisco Content Security Management Appliance (SMA), both virtual and hardware versions
    • Cisco Web Security Appliance (WSA), both virtual and hardware versions

    Cisco Cloud Email Security (CES) includes the Cisco ESA and Cisco SMA as part of the service solution. Cisco provides regular maintenance of the products included in this solution. Customers can also request a software upgrade by contacting Cisco CES support.

    Determine Software Version

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

    ciscoesa> version
Current Version
===============
Product: Cisco IronPort X1070 Messaging Gateway(tm) Appliance
Model: X1070
Version: 8.5.3-051
.
.
.


    To determine whether a vulnerable version of Cisco AsyncOS Software is running on a Cisco SMA, administrators can use the version command in the SMA CLI. The following example shows the results for a device running Cisco AsyncOS Software version 9.1.1-005:

    ciscosma> version
Current Version
===============
Product: Cisco IronPort M670 Security Management(tm) Appliance
Model: M670
Version: 9.1.1-005
.
.
.


    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
.
.
.

    Products Confirmed Not Vulnerable

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

Workarounds

  • There are no workarounds that mitigate this vulnerability.

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 tables, the left column lists major releases of Cisco AsyncOS for Cisco ESA, Cisco AsyncOS for Cisco SMA, and Cisco AsyncOS for Cisco WSA Software. 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 advisories and which release includes fixes for those vulnerabilities:

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

    CSCus79774 - Cisco ESA TCP Flood Denial of Service Vulnerability

    Cisco AsyncOS for Cisco ESA Major Release First Fixed Release for This Vulnerability First Fixed Release for This Vulnerability and All Vulnerabilities Described in the Companion Advisories
    Prior to 8.0
    		 Affected; migrate to 8.5.7-042 or later Affected; migrate to 8.5.7-043 or later
    8.0 and 8.0.1
    		 Affected; migrate to 8.5.7-042 or later
    		 Affected; migrate to 8.5.7-043 or later
    8.0.2 Affected; migrate to
    9.1.1-023 or later         		Affected; migrate to 9.1.1-023 or later
    8.5 8.5.7-042 8.5.7-043 or later
    9.0 9.1.0-032 Affected; migrate to 9.1.1-023 or later
    9.1 9.1.0-032 9.1.1-023 or later
    9.5 Affected; migrate to 9.6.0-042 or later
    		 Affected; migrate to 9.6.0-046 or later
    9.6 9.6.0-042 9.6.0-046 or later
    9.7 Not affected Not affected


    CSCus79777 - Cisco SMA TCP Flood Denial of Service Vulnerability

    Cisco AsynOS for Cisco SMA Major Release First Fixed Release for This Advisory First Fixed Release for This Vulnerability and All Vulnerabilities Described in the Companion Advisories
    Prior to 8.1
    		Affected; migrate to 9.1.0-031 or later
    		 Affected; migrate to 9.1.0-031 or later
    8.1 Affected; migrate to 9.1.0-031 or later Affected; migrate to 9.1.0-031 or later
    8.3 Affected; migrate to 9.1.0-031 or later Affected; migrate to 9.1.0-031 or later
    8.4 Affected; migrate to 9.1.0-031 or later Affected; migrate to 9.1.0-031 or later
    9.0 Affected; migrate to 9.1.0-031 or later Affected; migrate to 9.1.0-031 or later
    9.1 9.1.0-031 9.1.0-031 or later
    9.1.1 9.1.1-005 9.1.1-005 or later
    9.5 9.5.0-025 9.5.0-025 or later


    CSCzv95795 - Cisco WSA TCP Flood Denial of Service Vulnerability

    Cisco AsyncOS for Cisco WSA Major Release First Fixed Release for This Advisory First Fixed Release for This Vulnerability and All Vulnerabilities Described in the Companion Advisories
    Prior to 7.7 7.7.0-725
    		 Affected; migrate to 7.7.0-761 or later
    7.7
    		 7.7.0-725
    		 7.7.0-761
    8.0 8.0.8-113 8.0.8-113 or later
    8.1 Not affected 8.5.3.-051 or later
    8.5 Not affected 8.5.3-051 or later
    8.6 Not affected 8.7.0-171-LD or later
    8.7 Not affected 8.7.0-171-LD or later
    8.8 Not affected 8.8.0-085 or later
    9.0 Not affected Not affected

    In most cases an ESA, SMA, or 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 customer cases.

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
    1.3 Added steps for upgrading a device by using the GUI. Fixed Software Final 2015-November-20
    1.2 Added information about CES maintenance and upgrades. Vulnerable Products Final 2015-November-16
    1.1 Corrected the version number of the first fixed release for SMA major release 9.1. Fixed Software Final 2015-November-16
    1.0 Initial public release. - Final 2015-November-04
    Show Less

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