A vulnerability in SSL/TLS message handler for Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability exists because incoming SSL/TLS packets are not properly processed. An attacker could exploit this vulnerability by sending a crafted SSL/TLS packet to an affected device. A successful exploit could allow the attacker to cause the affected device to reload, resulting in a DoS condition. 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-asaftd-dos-4ygzLKU9 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 SSL/TLS message handler for Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device.
This vulnerability exists because incoming SSL/TLS packets are not properly processed. An attacker could exploit this vulnerability by sending a crafted SSL/TLS packet to an affected device. A successful exploit could allow the attacker to cause the affected device to reload, resulting in a DoS condition.
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-asaftd-dos-4ygzLKU9
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 products if they are running a vulnerable release of Cisco ASA Software or Cisco FTD Software and have a vulnerable AnyConnect or WebVPN configured.
For information about which Cisco software releases are vulnerable, see the Fixed Software section of this advisory.
To determine if a device is configured for AnyConnect IKEv2 Remote Access, AnyConnect SSL VPN, or Clientless SSL VPN, use the show running-config CLI command. In the following table, the left column lists the Cisco ASA features that are vulnerable. The right column indicates the vulnerable configuration for the feature from the show running-config CLI command. If the device is configured for one of these features, it is considered vulnerable.
| Cisco ASA Feature | Vulnerable Configuration |
|---|---|
| AnyConnect IKEv2 Remote Access (with client services) |
crypto ikev2 enable |
| AnyConnect SSL VPN |
webvpn |
| Clientless SSL VPN |
webvpn |
To determine if a device is configured for AnyConnect IKEv2 Remote Access or AnyConnect SSL VPN, use the show running-config CLI command. In the following table, the left column lists the Cisco FTD features that are vulnerable. The right column indicates the basic configuration for the feature from the show running-config CLI command. If the device is configured for one of these features, it is considered vulnerable.
On devices running Cisco FTD Software, the show running-config command is available from Diagnostic CLI mode only. To enter Diagnostic CLI mode, use the system support diagnostic-cli command in the regular Cisco Firepower Threat Defense CLI.
| Cisco FTD Feature | Vulnerable Configuration |
|---|---|
| AnyConnect IKEv2 Remote Access (with client services)1,2 |
crypto ikev2 enable |
| AnyConnect SSL VPN1,2 |
webvpn |
2. Remote Access VPN features were first supported in Cisco FTD Software Release 6.2.2.
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 Cisco Firepower Management (FMC) Software.
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 | Migrate to a fixed release. | Migrate to a fixed release. |
| 9.8 | 9.8.4.40 | 9.8.4.40 |
| 9.91 | Migrate to a fixed release. | Migrate to a fixed release. |
| 9.101 | Migrate to a fixed release. | Migrate to a fixed release. |
| 9.12 | 9.12.4.26 | 9.12.4.29 |
| 9.131 | Migrate to a fixed release. | Migrate to a fixed release. |
| 9.14 | 9.14.3.9 | 9.14.3.9 |
| 9.15 | 9.15.1.17 | 9.15.1.17 |
| 9.16 | Not vulnerable. | 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 | Migrate to a fixed release. | Migrate to a fixed release. |
| 6.2.3 | 6.2.3.17 | 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 | Not vulnerable. | 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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