Quantum Secular Labs / Blog / Advisories

CVE-2025-53521: F5 BIG-IP Stack-Based Buffer Overflow Vulnerability

CVE-2025-53521 is rated critical with a CVSS v3.1 base score of 9.8 and affects F5 BIG-IP. Per its scoring, it can be exploited over the network, without authentication, without any user interaction. The scored impact on confidentiality, integrity and availability is the highest available. CISA added it to its Known Exploited Vulnerabilities catalog on 2026-03-27, which means exploitation in the wild has been observed.

Vulnerability description

When a BIG-IP APM access policy is configured on a virtual server, specific malicious traffic can lead to Remote Code Execution (RCE).   Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.

Severity breakdown

CVSS v3.1 9.8: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

  • Attack vector: Network. Exploitable remotely over the network, with no need for local or physical access.
  • Attack complexity: Low. No special conditions; the attack can be repeated reliably.
  • Privileges required: None. No account or prior access is needed.
  • User interaction: None. No action from any user is needed.
  • Scope: Unchanged. Impact stays within the vulnerable component.
  • Confidentiality impact: High. Total loss of confidentiality; sensitive data can be fully disclosed.
  • Integrity impact: High. Total loss of integrity; data or system state can be fully modified.
  • Availability impact: High. Total loss of availability; the component can be shut down.

Underlying weakness

CWE-121: Stack-based Buffer Overflow

The product writes past the end of a buffer that was allocated on the stack.

Affected products

  • F5 Big IP Access Policy Manager: from 15.1.0 before 15.1.10.8; from 16.1.0 before 16.1.6.1; from 17.1.0 before 17.1.3; from 17.5.0 before 17.5.1.3

References