CVE-2025-20251
Published: 14 August 2025
Summary
CVE-2025-20251 is a high-severity Improper Validation of Specified Type of Input (CWE-1287) vulnerability in Cisco Secure Firewall (inferred from references). Its CVSS base score is 8.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Application or System Exploitation (T1499.004); ranked at the 34.7th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 SI-10 (Information Input Validation) and SI-2 (Flaw Remediation).
Threat & Defense at a Glance
Threat & Defense Details
Mitigating Controls (NIST 800-53 r5)AI
Directly addresses the insufficient input validation in HTTP requests to the SSL VPN service that enables arbitrary file creation or deletion on the OS.
Requires timely installation of software updates to remediate the specific input validation vulnerability in Cisco ASA/FTD SSL VPN software.
Enforces access control policies to limit authenticated VPN users from performing unauthorized file operations on the underlying OS.
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Vulnerability enables direct exploitation of crafted HTTP requests for arbitrary file manipulation on the VPN service, resulting in targeted DoS via application/system crash or disruption.
NVD Description
A vulnerability in the Remote Access SSL VPN service for Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an authenticated, remote attacker to create or delete arbitrary files on the…
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underlying operating system. If critical system files are manipulated, new Remote Access SSL VPN sessions could be denied and existing sessions could be dropped, causing a denial of service (DoS) condition. An exploited device requires a manual reboot to recover. This vulnerability is due to insufficient input validation when processing HTTP requests. An attacker could exploit this vulnerability by sending crafted HTTP requests to an affected device. A successful exploit could allow the attacker to create or delete files on the underlying operating system, which could cause the Remote Access SSL VPN service to become unresponsive. To exploit this vulnerability, the attacker must be authenticated as a VPN user of the affected device.
Deeper analysisAI
CVE-2025-20251 is a vulnerability in the Remote Access SSL VPN service of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software. It stems from insufficient input validation when processing HTTP requests, enabling an authenticated, remote attacker to create or delete arbitrary files on the underlying operating system. Manipulation of critical system files can deny new Remote Access SSL VPN sessions and drop existing ones, resulting in a denial-of-service (DoS) condition that requires a manual reboot for recovery. The vulnerability has a CVSS v3.1 base score of 8.5 (AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:L/A:H) and is associated with CWE-1287.
To exploit this vulnerability, an attacker must first authenticate as a VPN user on the affected device. Once authenticated, the attacker can send crafted HTTP requests to the Remote Access SSL VPN service, allowing arbitrary file creation or deletion on the operating system. Successful exploitation primarily enables a DoS on the VPN service by targeting critical files, rendering it unresponsive without impacting confidentiality but with high availability impact and some integrity effects due to the scoped privilege escalation.
Cisco has published a security advisory detailing this issue, available at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-http-file-hUyX2jL4, which provides information on affected versions and recommended mitigation steps, including software updates.
Details
- CWE(s)