CVE-2025-53521: F5 BIG-IP Stack-Based Buffer Overflow Vulnerability

Is it exploited?

Yes. CISA added it to the Known Exploited Vulnerabilities catalog on 27 Mar 2026, 163 days after the CVE record was published.

How likely is exploitation in the next 30 days?

2.3%

EPSS score, percentile 83.2 of all scored records

How severe?

9.3 Critical

CVSS v4.0 base score, given by the CNA

What should I do?

CISA deadline 30 Mar 2026. Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

Advisories and patches (1)

Which versions are affected?

Affected

• from 17.5.0 to before 17.5.1.3
• from 17.1.0 to before 17.1.3
• from 16.1.0 to before 16.1.6.1
• from 15.1.0 to before 15.1.10.8

Versions by product

Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

What to do

CISA due date for this action: 30 March 2026.

Advisories and patches

• my.f5.com (Vendor advisory)

Linked from CISA's catalog entry

• 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

Affected products and versions

As listed in the CVE record.

Versions not listed are: unknown.

Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

About this vulnerability

F5 BIG-IP APM contains a stack-based buffer overflow vulnerability that could allow a threat actor to achieve remote code execution.

Summary: CISA's KEV catalog, as of 28 Oct 2026.

• CISA added CVE-2025-53521 to its Known Exploited Vulnerabilities (KEV) catalog on 27 Mar 2026.
• CISA's ransomware flag for this entry is "Unknown": no evidence of ransomware use in the catalog, which is not proof of none.
• The due date CISA sets for the required action is 30 Mar 2026.
• The CVE record was published on 15 Oct 2025, 163 days before it was added to KEV.
• The CVE record carries a CVSS v4.0 base score of 9.3 (Critical), given by its CNA.
• FIRST's EPSS model puts the probability of exploitation in the next 30 days at 2.3% (percentile 83.2), as of 28 Oct 2026.
• CISA's SSVC assessment in the CVE record: exploitation active, automatable yes, technical impact total.

Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026. About the data.

Description

BigIP APM Vulnerability

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.

Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

Weakness

• CWE-121: Stack-based Buffer Overflow

CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record and the KEV entry.

Timeline

More exploited F5 vulnerabilities

• CVE-2026-94127: F5 BIG-IP APM Heap-based Buffer Overflow Vulnerability (added 22 Sep 2026)
• CVE-2023-46747: F5 BIG-IP Configuration Utility Authentication Bypass Vulnerability (added 31 Oct 2023)
• CVE-2023-46748: F5 BIG-IP Configuration Utility SQL Injection Vulnerability (added 31 Oct 2023)
• CVE-2022-1388: F5 BIG-IP Missing Authentication Vulnerability (added 10 May 2022)
• CVE-2021-22991: F5 BIG-IP Traffic Management Microkernel Buffer Overflow (added 18 Jan 2022)
• CVE-2020-5902: F5 BIG-IP Traffic Management User Interface (TMUI) Remote Code Execution Vulnerability (added 3 Nov 2021)