Cisco Firewall 0-Day Vulnerability Exploited in the Wild to Trigger DoS Condition
Brief
Security teams managing Cisco edge infrastructure face a high-priority patching deadline after Cisco confirmed active exploitation of a newly disclosed zero-day in its firewall VPN stack.
Tracked as CVE-2026-20349, the flaw affects the Remote Access SSL VPN service in Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software and can force an unexpected device reload, creating a denial-of-service condition for remote access and related network paths.
According to Cisco’s security advisory, the vulnerability stems from insufficient error checking when the SSL VPN service processes HTTP requests. An unauthenticated remote attacker can exploit the issue by sending a crafted HTTP request to the Remote Access SSL VPN service on an exposed device. No valid credentials are required.