Cisco Warns of Actively Exploited Firewall Vulnerability

Cisco is warning customers of a critical vulnerability in its firewall software that is being actively exploited by hackers to crash devices and disrupt services. The flaw, tracked as CVE-2026-20349, affects the company's Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) software. Cisco issued an advisory on Tuesday, August 11, 2026, stating that the vulnerability allows an unauthenticated, remote attacker to cause affected devices to reload unexpectedly, resulting in a denial-of-service condition.

The vulnerability stems from a failure in the software to properly check for errors when processing HTTP requests. Attackers can exploit this by sending specially crafted, error-ridden HTTP requests to the Remote Access SSL VPN service on the firewalls. This can trigger a reload loop, severing active connections and creating a continuous availability blackout. A crashed firewall stops logging and policy enforcement, potentially allowing malicious traffic to slip through and creating significant visibility loss for security teams.

Cisco said it discovered the bug internally with the help of an external security researcher and became aware of...