Cisco Security Advisory
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CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:C/C:N/I:L/A:N/E:X/RL:X/RC:X
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A vulnerability in the automatic decryption process in Cisco Umbrella Secure Web Gateway (SWG) could allow an authenticated, adjacent attacker to bypass the SSL decryption and content filtering policies on an affected system.
This vulnerability is due to how the decryption function uses the TLS Sever Name Indication (SNI) extension of an HTTPS request to discover the destination domain and determine if the request needs to be decrypted. An attacker could exploit this vulnerability by sending a crafted request over TLS from a client to an unknown or controlled URL. A successful exploit could allow an attacker to bypass the decryption process of Cisco Umbrella SWG and allow malicious content to be downloaded to a host on a protected network.
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-uswg-fdbps-xtTRKpp6
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Vulnerable Products
This vulnerability affects Cisco Umbrella SWG, which is cloud based.
Products Confirmed Not Vulnerable
Only products listed in the Vulnerable Products section of this advisory are known to be affected by this vulnerability.
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As a workaround, use the instructions in the Cisco Umbrella Secure Internet Gateway (SIG) User Guide to create a rule to block traffic that could bypass the SSL decryption and content filtering policies.
Step 1: Follow the instructions in the Add a Web Destination List section to create destination lists to control identity access to websites.
Step 2: Follow the instructions in the Add a Ruleset to the Web Policy to create a ruleset.
Step 3: Follow the instructions in the Add Rules to a Ruleset section to create a Block rule.
- From the Rule Action drop-down list, choose Block.
- Under Destinations, click Add Destination and then click Destination Lists. From the drop-down menu, choose the destination lists that were created in Step 1.
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 plans to address this vulnerability in Cisco Umbrella SWG, which is cloud based. No user action is required.
Customers who need additional information are advised to contact Cisco Umbrella Support at umbrella-support@cisco.com or their contracted maintenance providers.
For additional information, see the SWG Proxy handles non-standard HTTPs request article in the Cisco Umbrella SWG Knowledge Base.
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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Cisco would like to thank the security researchers Alexandre Samuel and Damien Foulde of Axians for reporting this vulnerability.
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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 summary section to accurately describe the protocol in use. Summary Final 2022-APR-29 1.0 Initial public release. — Final 2022-APR-20
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