Cisco Security Advisory
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CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X
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A vulnerability in the proxy service of Cisco AsyncOS for Cisco Web Security Appliance (WSA) could allow an unauthenticated, remote attacker to exhaust system memory and cause a denial of service (DoS) condition on an affected device.
This vulnerability is due to improper memory management in the proxy service of an affected device. An attacker could exploit this vulnerability by establishing a large number of HTTPS connections to the affected device. A successful exploit could allow the attacker to cause the system to stop processing new connections, which could result in a DoS condition.
Note: Manual intervention may be required to recover from this situation.
Cisco has released software updates that address this vulnerability. There are 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-dos-fmHdKswk
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Vulnerable Products
This vulnerability affects Cisco AsyncOS for Cisco WSA, both virtual and hardware appliances.
For information about which Cisco software releases are vulnerable, see the Fixed Software section of this advisory.
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, both virtual and hardware appliances
- Secure Email and Web Manager, both virtual and hardware appliances
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Use the grep CLI command and search in the proxylogs for the string Accept handlers have been Disabled. If any line shows up in the terminal, the proxy process may be saturated and a device reload may be required to recover the normal functions.
Alternatively, obtain the Proxy Track Stats logs from the Cisco WSA (through Secure Copy Protocol or FTP) and search for an INFO line like the one in this example: INFO: MALLOC'ed memory size 361150328 MMAP'ed memory 448790528. If the first number (361150328 in this case), keeps increasing up to the second number (448790528), the device memory allocation is approaching its limit, and a device reload is necessary.
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There is a workaround that addresses this vulnerability. Customers can use the hidden diagnostic > PROXY > KICK command to restart the proxy process and reclaim memory.
While this workaround 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.
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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:
https://www.cisco.com/c/en/us/products/end-user-license-agreement.htmlAdditionally, 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 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
In the following table(s), the left column lists Cisco software releases. The right column indicates whether a release is affected by the vulnerability described in this advisory and the first release that includes the fix for this vulnerability. Customers are advised to upgrade to an appropriate fixed software release as indicated in this section.
Cisco AsyncOS for Cisco WSA Release First Fixed Release 11.5 Not affected 11.8 Not affected 12.0 12.0.3-005 12.5 12.5.2-011 14.0 14.0.1-053 To update Cisco WSA devices over the network, complete the following steps:
- Choose System Administration > System Upgrade.
- Click Upgrade Options.
- Choose the option to Download and Install or, for an ESA, Download the upgrade.
- Choose the desired release.
- 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 will reboot.
The Cisco Product Security Incident Response Team (PSIRT) validates only the affected and fixed release information that is documented in this advisory.
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The Cisco 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 Cisco TAC 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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Show LessVersion Description Section Status Date 1.1 Updated fixed releases. Fixed Releases Final 2021-OCT-22 1.0 Initial public release. — Final 2021-OCT-06
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