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AUSCERT External Security Bulletin Redistribution
ESB-2023.0274.2
Cisco Email Security Appliance URL Filtering Bypass Vulnerability
14 February 2023
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AusCERT Security Bulletin Summary
---------------------------------
Product: Cisco Email Security Appliance (ESA)
Publisher: Cisco Systems
Operating System: Cisco
Resolution: Patch/Upgrade
CVE Names: CVE-2023-20057
Original Bulletin:
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-esa-url-bypass-WbMQqNJh
Comment: CVSS (Max): 4.7 CVE-2023-20057 (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N)
CVSS Source: Cisco Systems
Calculator: https://www.first.org/cvss/calculator/3.1#CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N
Revision History: February 14 2023: Updated the advisory SIR to informational
and summary to indicate the issue is not
exploitable. Also updated information about
vulnerable products and workarounds.
January 19 2023: Initial Release
- --------------------------BEGIN INCLUDED TEXT--------------------
Cisco Email Security Appliance URL Filtering Bypass Vulnerability
Priority: Informational
Advisory ID: cisco-sa-esa-url-bypass-WbMQqNJh
First Published: 2023 January 18 16:00 GMT
Last Updated: 2023 February 13 15:30 GMT
Version 1.1: Final
Workarounds: Yes
Cisco Bug IDs: CSCwb58117
CVE Names: CVE-2023-20057
Summary
o On January 18, 2023, Cisco disclosed the following:
A vulnerability in the URL filtering mechanism of Cisco AsyncOS
Software for Cisco Email Security Appliance (ESA) could allow an
unauthenticated, remote attacker to bypass the URL reputation filters
on an affected device.
This vulnerability is due to improper processing of URLs. An attacker
could exploit this vulnerability by crafting a URL in a particular way.
A successful exploit could allow the attacker to bypass the URL
reputation filters that are configured for an affected device, which
could allow malicious URLs to pass through the device.
After additional investigation, it was determined that this vulnerability
is not exploitable. For more information, see the Workarounds section of
this advisory.
This advisory is available at the following link:
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-esa-url-bypass-WbMQqNJh
Affected Products
o Vulnerable Products
At the time of publication, this vulnerability affected all releases of
Cisco AsyncOS Software for Cisco ESA that did not have the Anti-Spam
feature enabled.
See the Details section in the bug ID(s) at the top of this advisory for
the most complete and current information.
Products Confirmed Not Vulnerable
Only products listed in the Vulnerable Products section of this advisory
are known to be affected by this vulnerability.
Workarounds
o Administrators should follow the Best Practice Guide for Anti-Spam,
Anti-Virus, Graymail and Outbreak Filters and should ensure that the Cisco
Anti-Spam feature is enabled because it contains rules designed to identify
specially crafted URLs. It is also recommended that all positive verdicts
be either dropped or quarantined.
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 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.
Fixed Releases
For information about fixed software releases, see the Details section in
the bug ID(s) at the top of this advisory.
Exploitation and Public Announcements
o 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.
Source
o Cisco would like to thank Roy Barkay Yosef and Chen Farchi for reporting
this vulnerability.
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.
Subscribe to Cisco Security Notifications
o Subscribe
Related to This Advisory
o
URL
o https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-esa-url-bypass-WbMQqNJh
Revision History
o +---------+--------------------------+-------------+--------+-------------+
| Version | Description | Section | Status | Date |
+---------+--------------------------+-------------+--------+-------------+
| | Updated the advisory SIR | | | |
| | to Informational. | | | |
| | Updated the Summary to | Header, | | |
| | indicate that the issue | Summary, | | |
| 1.1 | is not exploitable. | Affected | Final | 2023-FEB-13 |
| | Updated information | Products, | | |
| | about vulnerable | Workarounds | | |
| | products. Updated the | | | |
| | Workarounds section. | | | |
+---------+--------------------------+-------------+--------+-------------+
| 1.0 | Initial public release. | - | Final | 2023-JAN-18 |
+---------+--------------------------+-------------+--------+-------------+
Legal Disclaimer
o THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND
OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR
FITNESS FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT
OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES
THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.
A standalone copy or paraphrase of the text of this document that omits the
distribution URL is an uncontrolled copy and may lack important information
or contain factual errors. The information in this document is intended for
end users of Cisco products.
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