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CVE-2025-53521

Critical CVSS 9.8 Known exploited

Published 2025-10-15 · last changed 2026-06-17 · added to CISA KEV 2026-03-27

This one is being exploited in the wild.

CISA added CVE-2025-53521 to the Known Exploited Vulnerabilities catalog on 2026-03-27. Federal agencies are required to remediate it on a deadline. If you have affected machines, this is the class of finding that moves ahead of the rest of the queue.

The fix

We hold no Microsoft remediation data for CVE-2025-53521, which normally means it is not a Windows CVE. For non-Microsoft software the fix is the vendor's own updated release, and the affected versions are listed below.

What it is

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.

Sources

CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H