The U.S. Cybersecurity and Infrastructure Security Agency (CISA) adds a flaw in F5 BIG-IP AMP to its Known Exploited Vulnerabilities catalog.
The U.S. Cybersecurity and Infrastructure Security Agency (CISA) added a flaw in F5 BIG-IP AMP, tracked as CVE-2025-53521 (CVSS ver. 3.1 score of 9.8), to its Known Exploited Vulnerabilities (KEV) catalog.
The vulnerability in BIG-IP APM allows specially crafted malicious traffic to trigger Remote Code Execution (RCE) when an access policy is enabled on a virtual server.
“When a BIG-IP APM access policy is configured on a virtual server, specific malicious traffic can lead to Remote Code Execution (RCE).” reads the advisory. “Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.”
The flaw was previously classified as a Denial-of-Service (DoS) issue, which has been reclassified as a critical Remote Code Execution (RCE) flaw based on new findings in March 2026. Its severity has increased significantly, with higher CVSS scores. The original fix remains effective, but the flaw has been actively exploited in vulnerable BIG-IP versions.
“We have learned that this vulnerability has been exploited in the vulnerable BIG-IP versions below.” reads the vendor’s advisory.
F5 thanks Schuberg Philis, Bart Vrancken, Fox-IT, and the Dutch NCSC for their help in investigating the issue and ensuring a high-standard coordinated disclosure.
According to Binding Operational Directive (BOD) 22-01: Reducing the Significant Risk of Known Exploited Vulnerabilities, FCEB agencies have to address the identified vulnerabilities by the due date to protect their networks against attacks exploiting the flaws in the catalog.
Experts also recommend that private organizations review the Catalog and address the vulnerabilities in their infrastructure.
CISA orders federal agencies to fix the vulnerability by March 30, 2026.
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