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AV:N/AC:L/Au:N/C:N/I:N/A:C/E:H/RL:OF/RC:C
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A vulnerability in the cached 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 due to the appliance running out of system memory.
The vulnerability is due to a failure to free memory when a file range for cached content is requested through the WSA. An attacker could exploit this vulnerability by opening multiple connections that request file ranges through the affected device. 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 addresses this vulnerability is also available.
This advisory is available at the following link:
http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20160518-wsa2
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Vulnerable Products
This vulnerability affects Cisco AsyncOS versions for Cisco WSA on both virtual and hardware appliances. See the "Fixed Software" section of this security advisory for additional information about the affected software versions.
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 command-line interface (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
.
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.Products Confirmed Not Vulnerable
No other Cisco products are currently known to be affected by this vulnerability.
The following products are not affected by this vulnerability:
- Email Security Appliance (ESA), both virtual and hardware versions
- Security Mail Appliance (SMA), both virtual and hardware versions
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The indicator of compromise for this vulnerability is an accumulation of TCP connections that will not be freed, which can lead to memory exhaustion. To determine whether there is an accumulation of TCP 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 as a possible indicator of this vulnerability.
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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 diagnostic -> PROXY -> KICK hidden command to restart the proxy process and reclaim memory.
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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: http://www.cisco.com/en/US/docs/general/warranty/English/EU1KEN_.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 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.
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 Technical Assistance Center (TAC): http://www.cisco.com/en/US/support/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 should upgrade to an appropriate release as indicated in this section. To help ensure a complete upgrade solution, consider that this advisory is part of a collection that includes the following advisories:
- cisco-sa-20160518-wsa1: Cisco Web Security Appliance HTTP POST Denial of Service Vulnerability
- cisco-sa-20160518-wsa2: Cisco Web Security Appliance Cached Range Request Denial of Service Vulnerability
- cisco-sa-20160518-wsa3: Cisco Web Security Appliance HTTP Length Denial of Service Vulnerability
- cisco-sa-20160518-wsa4: Cisco Web Security Appliance Connection Denial of Service Vulnerability
Customers should upgrade to an appropriate release as indicated in the following table:
Cisco AsyncOS Software
Major ReleaseFirst Fixed Release for
This VulnerabilityFirst Fixed Release for
This Vulnerability and
All Vulnerabilities Described in
the Collection of AdvisoriesPrior to 7.7 Not affected 9.0.1-162
7.7 Not affected 9.0.1-162 8.0 Not affected 9.0.1-162 8.5 Affected; migrate to 9.0.1-162 or later
9.0.1-162 8.6 Affected; migrate to 9.0.1-162 or later
9.0.1-162 8.7 Affected; migrate to 9.0.1-162 or later 9.0.1-162 8.8 Affected; migrate to 9.0.1-162 or later 9.0.1-162 9.0 9.0.1-162 9.0.1-162 9.1 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:
Choose System Administration > System Upgrade.
Click Upgrade Options.
Choose Download and Install.
Choose the release to upgrade to.
In the Upgrade Preparation area, choose the appropriate options.
Click Proceed to begin the upgrade. A progress bar displays the status of the upgrade.
After the upgrade is complete, the device reboots.
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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.
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This vulnerability was found during the resolution of a support case.
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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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Version Description Section Status Date 1.0 Initial public release. — Final 2016-May-18
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