A vulnerability in traffic-monitoring functions in Cisco Web Security Appliance (WSA) could allow an unauthenticated, remote attacker to circumvent Layer 4 Traffic Monitor (L4TM) functionality and bypass security protections. The vulnerability is due to a change in the underlying operating system software that is responsible for monitoring affected traffic. An attacker could exploit this vulnerability by sending crafted IP packets to an affected device. A successful exploit could allow the attacker to pass traffic through the device, which the WSA was configured to deny. This vulnerability affects both IPv4 and IPv6 traffic. 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://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180606-wsa
This vulnerability affects Cisco AsyncOS versions for WSA on both virtual and hardware appliances running any release of the 10.5.1, 10.5.2, or 11.0.0 WSA Software. See the Fixed Software section of this security advisory for additional information about affected software releases.
The WSA is vulnerable if it is configured for L4TM. To check whether a WSA is configured for L4TM, administrators can navigate to the L4 Traffic Monitor configuration settings:
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 10.5.1-296:
Vulmon
ciscowsa> version
Current Version
===============
Product: Cisco IronPort S670 Web Security Appliance
Model: S670
Version: 10.5.1-296
.
.
.
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:
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.
In the following table, the left column lists major releases of Cisco AsyncOS for WSA Software. The right 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.
Customers should upgrade to an appropriate release as indicated in the following table:
| Cisco AsyncOS WSA Software Major Release | First Fixed Release for This Vulnerability |
|---|---|
| Prior to 10.5.1 |
Not vulnerable |
| 10.5.1 |
10.5.2-042 |
| 10.5.2 | 10.5.2-042 |
| 11.0.0 | 11.5.0-0614 |
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:
After the upgrade is complete, the device reboots.
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.
This vulnerability was found during the resolution of a Cisco TAC support case.
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.
| Version | Description | Section | Status | Date |
|---|---|---|---|---|
| 1.1 | Updated fixed release information to reflect availability of Release 10.5.2-042. | Fixed Software | Final | 2018-June-08 |
| 1.0 | Initial public release. | - | Final | 2018-June-06 |
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