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AUSCERT External Security Bulletin Redistribution
ESB-2021.3323.2
Cisco Web Security Appliance Proxy Service Denial of Service Vulnerability
25 October 2021
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AusCERT Security Bulletin Summary
---------------------------------
Product: Web Security Appliance
Publisher: Cisco Systems
Operating System: Cisco
Impact/Access: Denial of Service -- Remote/Unauthenticated
Resolution: Patch/Upgrade
CVE Names: CVE-2021-34698
Original Bulletin:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-wsa-dos-fmHdKswk
Revision History: October 25 2021: Vendor updated fixed releases
October 7 2021: Initial Release
- --------------------------BEGIN INCLUDED TEXT--------------------
Cisco Web Security Appliance Proxy Service Denial of Service Vulnerability
Priority: High
Advisory ID: cisco-sa-wsa-dos-fmHdKswk
First Published: 2021 October 6 16:00 GMT
Last Updated: 2021 October 22 15:18 GMT
Version 1.1: Final
Workarounds: Yes
Cisco Bug IDs: CSCvv43704 CSCvw11261 CSCvz00720
CVE Names: CVE-2021-34698
CWEs: CWE-401
Summary
o 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://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-wsa-dos-fmHdKswk
Affected Products
o 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
Indicators of Compromise
o 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.
Workarounds
o 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.
Fixed Software
o 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 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:
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 desired release.
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 will reboot.
The Cisco Product Security Incident Response Team (PSIRT) validates only
the affected and fixed release information that is documented in this
advisory.
Exploitation and Public Announcements
o The Cisco PSIRT is not aware of any public announcements or malicious use
of the vulnerability that is described in this advisory.
Source
o This vulnerability was found during the resolution of a Cisco TAC support
case.
Cisco Security Vulnerability Policy
o 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.
URL
o https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-wsa-dos-fmHdKswk
Revision History
o +---------+------------------------+---------------+--------+-------------+
| Version | Description | Section | Status | Date |
+---------+------------------------+---------------+--------+-------------+
| 1.1 | Updated fixed | Fixed | Final | 2021-OCT-22 |
| | releases. | Releases | | |
+---------+------------------------+---------------+--------+-------------+
| 1.0 | Initial public | - | Final | 2021-OCT-06 |
| | release. | | | |
+---------+------------------------+---------------+--------+-------------+
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