Summary

• A vulnerability in the web proxy functionality of Cisco AsyncOS Software for Cisco Web Security Appliances could allow an unauthenticated, remote attacker to exhaust system memory and cause a denial of service (DoS) condition on an affected system.

  The vulnerability exists because the affected software improperly manages memory resources for TCP connections to a targeted device. An attacker could exploit this vulnerability by establishing a high number of TCP connections to the data interface of an affected device via IPv4 or IPv6. A successful exploit could allow the attacker to exhaust system memory, which could cause the system to stop processing new connections and result in a DoS condition. System recovery may require manual intervention.

  Cisco has released software updates that address this vulnerability. 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-20180815-wsa-dos

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco AsyncOS Software Releases 9.1, 10.1, 10.5, and 11.0 for Cisco Web Security Appliances, both virtual and hardware appliances, if the HTTPS Proxy feature is enabled. By default, the HTTPS Proxy feature is disabled.

  For more information about which Cisco AsyncOS Software releases are vulnerable, see the Fixed Software section of this advisory.

  To determine whether a vulnerable release of Cisco AsyncOS Software is running on a Cisco Web Security Appliance (WSA), administrators can use the version command in the WSA CLI. The following example shows the output of the command for a WSA that is running Cisco AsyncOS Software Release 10.5.2-072:

  ciscowsa> version

  Current Version
  ===============
  Product: Cisco S670 Web Security Appliance
  Model: S670
  Version: 10.5.2-072
  .
  .
  .

  To determine whether the HTTPS Proxy feature is enabled for a WSA, administrators can log in to the web interface of the WSA and navigate to Security Services > HTTPS Proxy. The value in the HTTPS Proxy field indicates whether the feature is enabled or disabled.

  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:

  • Email Security Appliance (ESA), both virtual and hardware appliances
  • Security Management Appliance (SMA), both virtual and hardware appliances

Indicators of Compromise

• Exploitation of this vulnerability will cause the affected software to stop releasing memory resources that were allocated to established TCP connections, which could exhaust system memory on a device.

  Administrators can assess the current status of device connections by using the netstat command in the device CLI. If the output of the command indicates an accumulation of TCP connections in the CLOSE_WAIT state, the device may be affected by this vulnerability. The following example shows the output of the netstat command for a device that has not released memory resources for several TCP connections running over IPv4 and IPv6, respectively:

  ciscowsa> netstat
  
  .
  .
  .
  Active Internet connections (including servers)
  Proto Recv-Q Send-Q Local Address          Foreign Address        (state)
  tcp4       0      0 127.0.0.1.25255        127.0.0.1.36586        TIME_WAIT
  tcp4     112      0 127.0.0.1.443          127.0.0.1.9310         CLOSE_WAIT
  tcp4       0      0 127.0.0.1.9310         127.0.0.1.443          FIN_WAIT_2
  tcp4       0      0 127.0.0.1.25255        127.0.0.1.21834        TIME_WAIT
  tcp4     112      0 127.0.0.1.443          127.0.0.1.36782        CLOSE_WAIT
  tcp4       0      0 10.1.1.51.32969        1.1.1.1.443            ESTABLISHED
  tcp6     112      0 ::1.443                ::1.48808              CLOSE_WAIT
  tcp4       0      0 10.1.1.51.443          *.*                    LISTEN
  tcp6       0      0 ::1.443                *.*                    LISTEN
  tcp4       0      0 127.0.0.1.443          *.*                    LISTEN
  .
  .
  .

  To recover memory resources on a device, administrators can reboot the device or restart the web proxy process. To restart the web proxy process, administrators can use the hidden diagnostic > PROXY > kick command in the device CLI, for example:

  ciscowsa> diagnostic
  
  Choose the operation you want to perform:
  - NET - Network Diagnostic Utility.
  - PROXY - Proxy Debugging Utility.
  - REPORTING - Reporting Utilities.
  []> proxy
  
  - SNAP    - Take a snapshot of the proxy
  - OFFLINE - Take the proxy offline (via WCCP)
  - RESUME  - Resume proxy traffic via (via WCCP)
  - CACHE   - Clear proxy cache
  []> kick
  Kick the proxy?
  Are you sure you want to proceed? [N]> Y

  Note that web proxy services will be temporarily unavailable while the web proxy process restarts.

Workarounds

• There are no workarounds that address this vulnerability.

Fixed Software

• Cisco has released free software updates that address the vulnerability described in this advisory. Customers may only install and expect support for software versions and feature sets for which they have purchased a license. By installing, downloading, accessing, or otherwise using such software upgrades, customers agree to follow the terms of the Cisco software license:
  https://www.cisco.com/c/en/us/products/end-user-license-agreement.html

  Additionally, customers may only download software for which they have a valid license, procured from Cisco directly, or through a Cisco authorized reseller or partner. In most cases this will be a maintenance upgrade to software that was previously purchased. Free security software updates do not entitle customers to a new software license, additional software feature sets, or major revision upgrades.

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

  Customers Without Service Contracts

  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 TAC:
  https://www.cisco.com/c/en/us/support/web/tsd-cisco-worldwide-contacts.html

  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.

  Fixed Releases

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

  Cisco AsyncOS Software Major Release	First Fixed Release
  Prior to 9.1	Migrate to 10.1.3-054 or later
  9.1	Migrate to 10.1.3-054 or later
  10.1	10.1.3-054
  10.5	10.5.2-072
  11.0	11.5.0-614
  11.5	Not vulnerable

  In most cases, the software can be upgraded over the network by using the System Upgrade options in the web interface of the WSA. To upgrade a device by using the web interface:

  1. Choose System Administration > System Upgrade.
  2. Click Upgrade Options.
  3. Choose Download and Install.
  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 internal security testing.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180815-wsa-dos

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	-	Final	2018-August-15

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