CVE-2025-53521
F5 — F5 BIG-IP Stack-Based Buffer Overflow Vulnerability
F5 · CWE-121 — Stack-based buffer overflow · in CISA KEV since 2026-03-27
EVRS 75 of 100 Urgent
Patch This Cycle
Rank 1,221 of 2,960 tracked
Raised to the floor for a confirmed exploited vulnerability.
Why it scores 75
Evidence available: 6 of 7 signalsListed in the CISA KEV catalog, and an EPSS probability of 0.023.
- CISA KEVApplied
- RansomwareDid not apply
- Vendor exploitationDid not apply
- EPSSApplied
- Microsoft Exploitability IndexNot applicable
- Pre-patch disclosureNo data
- KEV recencyDid not apply
- CVSSApplied
The band answers “how soon”, not “how bad”. No data for: Pre-patch disclosure. Why some signals show no data
Fix
Patch or fixed version identifiedCISA required action
- Please adhere to F5’s guidelines to assess exposure and mitigate risks. Check for signs of potential compromise on all internet accessible F5 products affected by this vulnerability. For more information please see
- my.f5.com/…/K000160486
- my.f5.com/…/K11438344
- nvd.nist.gov/…/CVE-2025-53521
Fixed in
big-ip access policy manager: update to 15.1.10.8 or later | big-ip access policy manager: update to 16.1.6.1 or later | big-ip access policy manager: update to 17.1.3 or later | big-ip access policy manager: update to 17.5.1.3 or later
Affected versions
- big-ip access policy manager
>= 15.1.0 < 15.1.10.8>= 16.1.0 < 16.1.6.1>= 17.1.0 < 17.1.3>= 17.5.0 < 17.5.1.3
Remediation
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
Fixed versions from NVD.
Evidence
Each value with its source| Measure | Value | Source |
|---|---|---|
| CVSS base scoreHow severe the flaw is in itself. It does not say how likely an attack is. | 9.3 | NVD |
| FIRST EPSSFIRST's estimate of the chance this is exploited in the next 30 days, and how that ranks against all CVEs. | 0.023 (83.1st pctl) | FIRST EPSS |
| Actively exploitedWhether a source of record has confirmed attacks using it in the wild. | Confirmed | CISA KEV |
| Ransomware campaign useWhether CISA has seen ransomware operators use it. | Unknown or none | CISA KEV |
| CISA remediation deadlineThe date US federal agencies must have fixed or mitigated it. | 2026-03-30 · CISA federal deadline · Overdue by 7 months | CISA KEV |
| Public exploit moduleA module existing is not the same as active exploitation. | None known | Metasploit |
| EUVD cross-referenceENISA's record: CVSS 9.3 (v4.0), assigned by f5. | Listed | ENISA EUVD |
Description
NVDWhen 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.
What CISA says to do