A vulnerability in the software-based SSL/TLS message handler of Cisco Adaptive Security Appliance (ASA) Software and Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause an affected device to reload, resulting in a denial of service (DoS) condition. This vulnerability is due to insufficient validation of SSL/TLS messages when the device performs software-based SSL/TLS decryption. An attacker could exploit this vulnerability by sending a crafted SSL/TLS message to an affected device. A successful exploit could allow the attacker to cause the affected device to reload, resulting in a DoS condition. Note: Datagram TLS (DTLS) messages cannot be used to exploit this vulnerability. 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-ftd-tls-decrypt-dos-BMxYjm8M This advisory is part of the October 2021 release of the Cisco ASA, FTD, and FMC Security Advisory Bundled publication. For a complete list of the advisories and links to them, see Cisco Event Response: October 2021 Cisco ASA, FMC, and FTD Software Security Advisory Bundled Publication.
A vulnerability in the software-based SSL/TLS message handler of Cisco Adaptive Security Appliance (ASA) Software and Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause an affected device to reload, resulting in a denial of service (DoS) condition.
This vulnerability is due to insufficient validation of SSL/TLS messages when the device performs software-based SSL/TLS decryption. An attacker could exploit this vulnerability by sending a crafted SSL/TLS message to an affected device. A successful exploit could allow the attacker to cause the affected device to reload, resulting in a DoS condition.
Note: Datagram TLS (DTLS) messages cannot be used to exploit this vulnerability.
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-ftd-tls-decrypt-dos-BMxYjm8M
This advisory is part of the October 2021 release of the Cisco ASA, FTD, and FMC Security Advisory Bundled publication. For a complete list of the advisories and links to them, see Cisco Event Response: October 2021 Cisco ASA, FMC, and FTD Software Security Advisory Bundled Publication.
This vulnerability affects Cisco devices if they are running the following Cisco software releases under the following conditions:
| Cisco Software | Affected Releases | Vulnerability Details |
|---|---|---|
| ASA Software | 9.16.1 and 9.16.1.28 | If affected devices are configured to process inbound SSL/TLS message, they are vulnerable to crafted SSL/TLS message that are sent to the device. |
| FTD Software | 7.0.0 and 7.0.01 | |
| FTD Software | 6.3.0 and later, but earlier than the first fixed release | If affected devices are configured with an active SSL Decryption Policy, they are vulnerable to crafted SSL/TLS message that are sent through the device. |
For information about which Cisco software releases are vulnerable, see the Fixed Software section of this advisory.
To verify whether a device that is running Cisco ASA Software or Cisco FTD Software could process inbound SSL or TLS messages, use the show asp table socket | include SSL command and verify that it returns output. When this command returns any output, the device is vulnerable. When this command returns empty output, the device is not affected by the vulnerability described in this advisory. The following example shows the output of the show asp table socket | include SSL command from a device that is vulnerable:
# show asp table socket | include SSL
SSL 0005aa68 LISTEN 192.168.4.1:443 0.0.0.0:*
SSL 0018f7a8 LISTEN 192.168.4.1:8443 0.0.0.0:*
There are two methods for determining whether an SSL decryption policy is enabled:
Option 1: Use the CLI
Use the show ssl-policy-config CLI command to verify whether an SSL decryption policy is enabled on a device. The following example shows the output of the show ssl-policy-config command on a device that does not have an SSL policy configured and is not vulnerable:
> show ssl-policy-config
SSL policy not yet applied.
Any other output returned by the show ssl-policy-config command indicates that an SSL policy is configured and the device is affected by the vulnerability described in this advisory.
For more information about the show ssl-policy-config command, see the Cisco Firepower Threat Defense Command Reference.
Option 2: Use the GUI
To determine whether an SSL decryption policy is enabled on a device, check the appropriate policy:
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 when they are running Cisco FTD Software releases 6.3 through 6.7:
There are no workarounds that address this vulnerability.
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 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(s), the left column lists Cisco software releases. The center 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. The right column indicates whether a release is affected by any of the Critical or High SIR vulnerabilities described in this bundle and which release includes fixes for those vulnerabilities.
ASA Software
| Cisco ASA Software Release | First Fixed Release for This Vulnerability | First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories |
|---|---|---|
| 9.7 and earlier1 | Not vulnerable. | Migrate to a fixed release. |
| 9.8 | Not vulnerable. | 9.8.4.40 |
| 9.91 | Not vulnerable. | Migrate to a fixed release. |
| 9.101 | Not vulnerable. | Migrate to a fixed release. |
| 9.12 | Not vulnerable. | 9.12.4.29 |
| 9.131 | Not vulnerable. | Migrate to a fixed release. |
| 9.14 | Not vulnerable. | 9.14.3.9 |
| 9.15 | Not vulnerable. | 9.15.1.17 |
| 9.16 | 9.16.2 | 9.16.2.3 |
FTD Software
| Cisco FTD Software Release | First Fixed Release for This Vulnerability | First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories |
|---|---|---|
| 6.2.2 and earlier1 | Not vulnerable. | Migrate to a fixed release. |
| 6.2.3 | Not vulnerable. | Migrate to a fixed release. |
| 6.3.01 | Migrate to a fixed release. | Migrate to a fixed release. |
| 6.4.0 | 6.4.0.13 (Nov 2021) |
6.4.0.13 (Nov 2021) |
| 6.5.01 | Migrate to a fixed release. | Migrate to a fixed release. |
| 6.6.0 | 6.6.5 | 6.6.5.1 (Nov 2021) |
| 6.7.0 | 6.7.0.3 (Jan 2022) | 6.7.0.3 (Jan 2022) |
| 7.0.0 | 7.0.1 |
7.0.1 |
For instructions on upgrading your FTD device, see Cisco Firepower Management Center Upgrade Guide.
The Cisco Product Security Incident Response Team (PSIRT) validates only the affected and fixed release information that is documented in this advisory.
The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.
This vulnerability was found by Sanmith Prakash of Cisco during internal security testing.
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 |
|---|---|---|---|---|
| 1.0 | Initial public release. | - | Final | 2021-OCT-27 |
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