CVE-2025-53521 is a stack-based buffer overflow vulnerability (CWE-121) in F5 BIG-IP when an APM access policy is configured on a virtual server. This vulnerability can be triggered by specially crafted malicious traffic, leading to remote code execution on the affected system. It impacts multiple versions of BIG-IP (15.1.0, 16.1.0, 17.1.0, and 17.5.0). The vulnerability is rated critical with a CVSS v3.1 score of 9.8, reflecting network attack vector, no required privileges or user interaction, and high confidentiality, integrity, and availability impacts. No patch or vendor advisory details are provided, and no exploits are currently known in the wild.

Successful exploitation of this vulnerability allows an unauthenticated attacker to execute arbitrary code remotely on the vulnerable BIG-IP system, potentially leading to full system compromise. This can result in complete loss of confidentiality, integrity, and availability of the affected device. The vulnerability affects multiple supported versions of BIG-IP, but software versions that have reached End of Technical Support are not evaluated.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is released, organizations should consider disabling or not configuring the APM access policy on virtual servers if feasible, and monitor for any unusual traffic patterns targeting BIG-IP devices. Do not assume mitigation without vendor confirmation.