CISA Adds CVE-2025-53521 to KEV After Active F5 BIG-IP APM Exploitation
Mar 28, 2026
Vulnerability / Network Security
The U.S. Cybersecurity and Infrastructure Security Agency (CISA) on Friday added a critical security flaw impacting F5 BIG-IP Access Policy Manager (APM) to its Known Exploited Vulnerabilities ( KEV ) catalog, citing evidence of active exploitation. The vulnerability in question is CVE-2025-53521 (CVSS v4 score: 9.3), which could allow a threat actor to achieve remote code execution. "When a BIG-IP APM access policy is configured on a virtual server, specific malicious traffic can lead to Remote Code Execution (RCE)," according to a description of the flaw in CVE.org. While the shortcoming was initially categorized and remediated as a denial-of-service (DoS) vulnerability with a CVSS v4 score of 8.7, F5 said it has been reclassified as a case of RCE in light of "new information obtained in March 2026." The company has since updated its advisory to confirm that the vulnerability "has been exploited in the vulnerable BIG-IP versions." It did not shar...
