Cisco ASA/FTD SSL VPN flaw exploited
Actively exploited unauthenticated DoS vulnerability in Cisco Secure Firewall ASA/FTD SSL VPN can crash devices remotely; patches available.
Sourceadvisories.ncsc.nl — open the original
What to check
- Applies to
- The 1 CVE named below. Whether you run an affected version is not assessed: check the versions the source lists.
- Exploitation
- CISA lists CVE-2026-76418 as exploited in the wild.
NCSC-NL issued an advisory for CVE-2026-76418, a NULL pointer dereference vulnerability in the Remote Access SSL VPN functionality of Cisco Secure Firewall Adaptive Security Appliance (ASA) and Cisco Secure Firewall Threat Defense (FTD). The flaw carries a CVSS score of 8.6 and is confirmed by Cisco to be actively exploited in the wild. An unauthenticated attacker can remotely trigger the vulnerability by sending a specially crafted request to the VPN service, causing the affected device to unexpectedly reboot, resulting in a Denial-of-Service condition and disruption of VPN services.
Exploitation requires that the SSL VPN service be reachable and that secondary authentication is configured for a VPN tunnel group; a successful VPN login is not required to trigger the crash. Cisco has released software updates addressing the vulnerability. Defenders should verify whether secondary authentication is configured on their VPN tunnel groups, as this is a prerequisite for exploitation, and apply the available patches promptly given confirmed in-the-wild exploitation. Cisco has also described temporary mitigations, but cautions that these may reduce the security of VPN access and should be considered a stopgap rather than a substitute for patching.
Given this is an actively exploited, unauthenticated, remotely triggerable DoS affecting widely deployed perimeter VPN appliances, organizations using Cisco ASA/FTD with SSL VPN and secondary authentication enabled should prioritize patching and review exposure of the VPN service to the internet.
Mentioned in this report
Source reporting: https://advisories.ncsc.nl/2026/ncsc-2026-0463.html
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