How severe is CVE-2025-53521?

CVE-2025-53521 has a CVSS 3.1 base score of 9.8 (CRITICAL). EPSS estimates a 2.3% probability of exploitation in the next 30 days. It is listed in the CISA Known Exploited Vulnerabilities catalog.

CVE-2025-53521: BigIP APM

CISA Known Exploited Vulnerabilities

F5 BIG-IP Stack-Based Buffer Overflow Vulnerability is confirmed as actively exploited and is listed in the CISA KEV catalog.

Added to KEV

2026-03-27

Remediation due

2026-03-30

Required action
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

CISA notes
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: https://my.f5.com/manage/s/article/K000156741 ; https://my.f5.com/manage/s/article/K000160486 ; https://my.f5.com/manage/s/article/K11438344 ; https://nvd.nist.gov/vuln/detail/CVE-2025-53521

Description

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.

Severity

CVSS 3.1 · CNA9.8 CRITICAL

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

CVSS 4.0 · CNA9.3 CRITICAL

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

SSVC · CISA-ADP

Exploitationactive

Automatableyes

Technical impacttotal

Affected Products

Vendor	Product	Affected versions
F5	BIG-IP	17.5.0 to <17.5.1.3 17.1.0 to <17.1.3 16.1.0 to <16.1.6.1 15.1.0 to <15.1.10.8

References

1 Links

Vendor advisories

https://my.f5.com/manage/s/article/K000156741

Record Details

Published

2025-10-15

Last updated

2026-03-31

Assigner (CNA)

Credited to

F5 would like to thank Kristian Vlaardingerbroek, Hugo Trippaers, and other people of Schuberg Philis; Bart Vrancken; Fox-IT; and the National Cyber Security Centre (NCSC) in the Netherlands for their assistance in investigating this issue and following the highest standards of coordinated disclosure.

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CVE-2023-467488.8

BIG-IP Configuration utility authenticated SQL injection vulnerability

CVE-2026-941279.8

BIG-IP APM OAuth vulnerability

Related Tool Categories

Tool categories that test for or protect against this vulnerability class.

CWE-121 · Stack-based Buffer Overflow

Fuzzing Binary Exploitation

CVE record data © The MITRE Corporation, used under the CVE Terms of Use. Exploited-in-the-wild data from the CISA Known Exploited Vulnerabilities catalog (CC0). Exploit prediction scores by FIRST EPSS (first.org/epss). This site is not endorsed or certified by MITRE, NVD, CISA, or FIRST.