Cisco Security Advisory
Cisco Email Security Appliance Denial of Service Vulnerability
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CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:X/RL:X/RC:X
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A vulnerability in Cisco AsyncOS Software for Cisco Email Security Appliance (ESA) could allow an unauthenticated remote attacker to cause a denial of service (DoS) condition on an affected device.
This vulnerability is due to improper handling of certain TLS connections that are processed by an affected device. An attacker could exploit this vulnerability by establishing a large number of concurrent TLS connections to an affected device. A successful exploit could allow the attacker to cause the device to drop new TLS email messages that come from the associated email servers. Exploitation of this vulnerability does not cause the affected device to unexpectedly reload. The device will recover autonomously within a few hours of when the attack is halted or mitigated.
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://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-esa-dos-gdghHmbV
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Vulnerable Products
At the time of publication, this vulnerability affected Cisco ESA, both virtual and physical appliances, if they were running a vulnerable release of Cisco AsyncOS Software.
For information about which Cisco software releases were vulnerable at the time of publication, see the Fixed Software section of this advisory. 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.
Cisco has confirmed that this vulnerability does not affect the following Cisco products:
- Secure Email and Web Manager, formerly known as Cisco Content Security Management Appliance (SMA)
- Secure Web Appliance, formerly know as Cisco Web Security Appliance (WSA)
Attention: Simplifying the Cisco portfolio includes the renaming of security products under one brand: Cisco Secure. For more information, see Meet Cisco Secure.
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There are no workarounds that address this vulnerability.
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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
At the time of publication, the release information in the following table(s) was accurate. See the Details section in the bug ID(s) at the top of this advisory for the most complete and current information.
The left column lists Cisco software releases, and the right column indicates whether a release was affected by the vulnerabilities that are described in this advisory and which release included the fix for these vulnerabilities.
Cisco AsyncOS Software for Cisco ESA Release First Fixed Release 12.5.0 and earlier Migrate to a fixed release. 13.0 Migrate to a fixed release. 13.5 Migrate to a fixed release. 14.0 Migrate to a fixed release. 14.2 14.2.1-015 14.3 14.3.0-020 Cisco Cloud Email Security (CES) includes Cisco ESA and Cisco Secure Email and Web Manager devices as part of the service solution. Cisco provides regular maintenance of the products included in this solution. Customers can also request a software upgrade by contacting Cisco CES support.
In most cases, the software can be upgraded by using the System Upgrade options in the web interface of Cisco ESA. To upgrade a device by using the web interface, do the following:
- Choose System Administration > System Upgrade.
- Click Upgrade Options.
- Choose Download and Install.
- Choose the release to upgrade to.
- 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 1.0 Initial public release. - Final 2022-NOV-02
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