Cisco Security Advisory
Cisco Secure Firewall Adaptive Security Appliance and Secure Firewall Threat Defense Software for Firepower 2100 Series IPv6 over IPsec Denial of Service Vulnerability
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CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X
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A vulnerability in the RADIUS proxy feature for the IPsec VPN feature of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition.
This vulnerability is due to improper processing of IPv6 packets. An attacker could exploit this vulnerability by sending IPv6 packets over an IPsec VPN connection to an affected device. A successful exploit could allow the attacker to trigger a reload of the device, 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://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-fp2k-IPsec-dos-tjwgdZCOThis advisory is part of the August 2025 release of the Cisco Secure Firewall ASA, Secure FMC, and Secure FTD Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: August 2025 Semiannual Cisco Secure Firewall ASA, Secure FMC, and Secure FTD Software Security Advisory Bundled Publication.
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Vulnerable Products
This vulnerability affects Cisco Firepower 2100 Series Firewalls if they are running a vulnerable release of Cisco Secure Firewall ASA Software or Secure FTD Software and meet all the following conditions:
- IPsec VPN with Internet Key Exchange version 1 (IKEv1) or IKEv2 is enabled.
- IPv6 is enabled on the interface that is receiving RADIUS traffic.
- An access control list (ACL) is configured to permit IP traffic.1
1. This ACL configuration applies only to Cisco ASA Software releases 9.16 and earlier and Cisco FTD Software releases 7.0 and earlier.
For information about which Cisco software releases are vulnerable, see the Fixed Software section of this advisory.
Determine IKEv1 VPN Configuration
IKEv1 VPN is not enabled by default on any interface.
To determine whether IKEv1 VPN is enabled on any interface, use the show running-config crypto ikev1 | include crypto ikev1 enable CLI command. Non-empty output of this command indicates that IKEv1 VPN is enabled on the listed interface or interfaces. Empty output indicates that IKEv1 VPN is not enabled on any interface.
The following example shows the output of the show running-config crypto ikev1 | include crypto ikev1 enable command on a device that has IKEv1 VPN enabled on the outside interface:
> show running-config crypto ikev1 | include crypto ikev1 enable
crypto ikev1 enable outsideDetermine IKEv2 VPN Configuration
IKEv2 VPN is not enabled by default on any interface.
To determine whether IKEv2 VPN is enabled on any interface, use the show running-config crypto ikev2 | include crypto ikev2 enable CLI command. Non-empty output of this command indicates that IKEv2 VPN is enabled on the listed interface or interfaces. Empty output indicates that IKEv2 VPN is not enabled on any interface.
The following example shows the output of the show running-config crypto ikev2 | include crypto ikev2 enable command on a device that has IKEv2 VPN enabled on the outside interface:
> show running-config crypto ikev2 | include crypto ikev2 enable
crypto ikev2 enable outsideNote: The crypto ikev2 enable command may specify an additional client-services option that may include an optional port parameter. These options do not affect whether the device is affected by this vulnerability.
Determine IPv6 Configuration
To determine which interfaces have assigned IPv6 addresses on a device that has IPv6 enabled, use the show running-config | include interface | ipv6 CLI command, as shown in the following example:
> show running-config interface | include interface | ipv6
interface GigabitEthernet0/0
ipv6 address 2001:db8:0:1:192:168:1:12/64
ipv6 enableDetermine ACL Configuration
Note: This ACL configuration applies only to Cisco ASA Software releases 9.16 and earlier and Cisco FTD Software releases 7.0 and earlier.
To determine whether a control plane access group is configured use the show running-config access-group | include control-plane command. If a control plane access group is not configured, the device is not affected by this vulnerability.
Using the ACL-list-name of the access group from the output of the preceding command, run show access-list ACL-list-name to determine if the ACL is configured to permit IP traffic. If the output of the first command lists more than one ACL, check each ACL.
The following example shows the output of these commands on a device that has the ACL ACL-list-name configured to permit IP traffic:
> show running-config access-group | include control-plane
access-group ACL-list-name in interface outside control-plane
> show access-list ACL-list-name
access-list ACL-list-name line 1 extended permit ip any6 any6Products 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 Firewall ASA Software when running on platforms other than those listed in the Vulnerable Products section of this advisory
- Secure FTD Software when running on platforms other than those listed in the Vulnerable Products section of this advisory
- Secure Firewall Management Center (FMC) Software
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There are no workarounds that address this vulnerability.
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Cisco has released free software updates that address the vulnerability described in this advisory. Customers with service contracts that entitle them to regular software updates should obtain security fixes through their usual update channels.
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.htmlAdditionally, 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.
The Cisco Support and Downloads page on Cisco.com provides information about licensing and downloads. This page can also display customer device support coverage for customers who use the My Devices tool.
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 Without Service Contracts
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.
Cisco Secure Firewall ASA, Secure FMC, and Secure FTD Software
To help customers determine their exposure to vulnerabilities in Cisco Secure Firewall ASA, Secure FMC, and Secure FTD Software, Cisco provides the Cisco Software Checker. This tool identifies any Cisco security advisories that impact a specific software release and the earliest release that fixes the vulnerabilities that are described in each advisory (“First Fixed”). If applicable, the tool also returns the earliest release that fixes all the vulnerabilities that are described in all the advisories that the Software Checker identifies (“Combined First Fixed”).
To use the tool, go to the Cisco Software Checker page and follow the instructions. Alternatively, use the following form to search for vulnerabilities that affect a specific software release. To use the form, follow these steps:
- Choose which advisories the tool will search-all advisories, only advisories with a Critical or High Security Impact Rating (SIR), or only this advisory.
- Choose the appropriate software.
- Choose the appropriate platform.
- Enter a release number-for example, 9.20.3.4 for Cisco Secure Firewall ASA Software or 7.4.2 for Cisco Secure FTD Software.
- Click Check.
For instructions on upgrading a Cisco Secure FTD device, see the appropriate Cisco Secure FMC upgrade guide.
Additional Resources
For help determining the best Cisco Secure Firewall ASA, Secure FMC, or Secure FTD Software release, see the following Recommended Releases documents. If a security advisory recommends a later release, Cisco recommends following the advisory guidance.
Cisco Secure Firewall ASA Compatibility
Cisco Secure Firewall ASA Upgrade Guide
Cisco Secure Firewall Threat Defense Compatibility Guide
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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.
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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 1.1 Updated the vulnerable products configuration information. Vulnerable Products Final 2025-SEP-09 1.0 Initial public release. - Final 2025-AUG-14
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