CVE-2025-20333

The vulnerability stems from improper validation of user-supplied input data in HTTP(S) requests — classified as buffer overflow (CWE-120). An attacker with valid VPN user credentials can send crafted HTTP requests to the vulnerable device. Successful exploitation of the vulnerability allows execution of arbitrary code with root privileges in a context that exceeds the standard scope of the application (Scope: Changed).

An attacker can execute arbitrary code as root, which may result in complete takeover of the device, including its configuration, network traffic, and security mechanisms.

Security patches available from the vendor must be applied immediately in accordance with the official Cisco security advisory (cisco-sa-asaftd-webvpn-z5xP8EUB). Until the patch is installed, consider restricting access to the web VPN interface to trusted IP addresses only. Detailed guidance on patch versions is available at the addresses in the references section.

Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software — specific versions indicated in the vendor's references.

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.

Cisco Secure Firewall Adaptive Security (ASA) Appliance and Secure Firewall Threat Defense (FTD) Software VPN Web Server contain a buffer overflow vulnerability that allows for remote code execution. This vulnerability could be chained with CVE-2025-20362.