CVE-2025-20333
Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) Buffer Overflow Vulnerability
A vulnerability in the VPN web server of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an authenticated, remote attacker to execute arbitrary code on an affected device. This vulnerability is due to improper validation of user-supplied input in HTTP(S) requests. An attacker with valid VPN user credentials could exploit this vulnerability by sending crafted HTTP requests to an affected device. A successful exploit could allow the attacker to execute arbitrary code as root, possibly resulting in the complete compromise of the affected device.
The KEV due date refers to the deadline by which FCEB agencies are expected to review and begin implementing the guidance outlined in Emergency Directive (ED) 25-03 (URL listed below in Notes). Agencies must follow the mitigation steps provided by CISA (URL listed below in Notes) and vendor’s instructions (URL listed below in Notes). Adhere to the applicable BOD 22-01 guidance for cloud services or discontinue use of the product if mitigations are not available. Deadline for federal agencies: 2025-09-26.
3 articles across 3 outlets · first covered Apr 24, 2026 · latest Apr 25, 2026
Associated threat actors
Coverage timeline
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FIRESTARTER backdoor persists on patched Cisco ASA devicessecurityaffairs.com · Apr 25, 2026
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Cisco ASA Backdoor FIRESTARTER Persists After Patches, NCSC Warnsthehackernews.com · Apr 24, 2026
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US Agency Hit by Firestarter Backdoor on Cisco Firepower Gearwww.securityweek.com · Apr 24, 2026