Cyber Resilience

CVE-2025-53521

Memory Safety in F5 Big-Ip Access Policy Manager 15.1.0 – 15.1.10.8

CISA KEVActive ExploitationEUVD ExploitedUK NCSC AlertMemory Safety
Published
15 October 2025
Modified
31 March 2026
KEV Added
27 March 2026
Patch / advisory
View advisory
CVSS Score v4 9.3
Click a component to see what it means
Raw vectorCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
EPSS Score 0.022 81th percentile
Risk Priority 75 floored blend · peak EPSS

Summary

CVE-2025-53521 is a critical-severity Stack-based Buffer Overflow (CWE-121) vulnerability in F5 Big-Ip Access Policy Manager. Its CVSS base score is 9.3 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked in the top 19% of CVEs by exploit likelihood; CISA has added it to the Known Exploited Vulnerabilities catalog.

The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SI-10 (Information Input Validation) — see the control section below for these in your framework.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

CVE-2025-53521 is a remote code execution vulnerability affecting F5 BIG-IP APM when an access policy is configured on a virtual server. The flaw, assigned CWE-121, is triggered by specially crafted malicious traffic and carries a CVSS 4.0 score of 9.3 reflecting network attack vector, low complexity, and no required privileges or user interaction.

Unauthenticated attackers positioned on the network can send crafted requests to an affected virtual server and obtain arbitrary code execution with full control over confidentiality, integrity, and availability of the target system. Exploitation does not depend on authentication or user interaction.

F5’s security advisory K000156741 and the CISA Known Exploited Vulnerabilities catalog both address the issue and outline available mitigations, including patches for supported versions.

The vulnerability appears in CISA’s KEV catalog, confirming observed in-the-wild exploitation. Its EPSS score rose sharply from a low baseline to a peak of 0.4141 on 2026-04-01 before receding, indicating a clear post-disclosure increase in exploitation interest.

EU & UK References

Vulnerability Data

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.

CWE(s)
CWE-121
KEV Date Added
27 March 2026

Related Threats

MITRE ATT&CK Enterprise Techniques

T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
attack.mitre.org →
T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
T1203 Exploitation for Client Execution Execution
Adversaries may exploit software vulnerabilities in client applications to execute code.
attack.mitre.org →
T1210 Exploitation of Remote Services Lateral Movement
Adversaries may exploit remote services to gain unauthorized access to internal systems once inside of a network.
attack.mitre.org →
T1212 Exploitation for Credential Access Credential Access
Adversaries may exploit software vulnerabilities in an attempt to collect credentials.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2025-46405Same product: F5 Big-Ip Access Policy Manager
CVE-2026-40067Same product: F5 Big-Ip Access Policy Manager
CVE-2025-23412Same product: F5 Big-Ip Access Policy Manager
CVE-2025-36525Same product: F5 Big-Ip Access Policy Manager
CVE-2025-54854Same product: F5 Big-Ip Access Policy Manager
CVE-2025-61933Same product: F5 Big-Ip Access Policy Manager
CVE-2026-42919Same product: F5 Big-Ip Access Policy Manager
CVE-2026-41956Same product: F5 Big-Ip Access Policy Manager
CVE-2025-61960Same product: F5 Big-Ip Access Policy Manager
CVE-2023-22341Same product: F5 Big-Ip Access Policy Manager

Affected Assets

f5
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

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)
  • 2 hardening rules · 2 OS baselines
Validate
Prove the fix (OWASP ASVS)

—

Mitigating Controls (NIST 800-53 r5) AI

SA-11 Developer Testing and Evaluation good match

Developer testing and analysis can discover stack-buffer overflows before deployment.

SI-10 Information Input Validation good match

Input validation directly stops untrusted data from exceeding stack buffer bounds.

SI-16 Memory Protection good match

Memory-protection mechanisms limit the ability to execute injected code after a stack overflow.

SA-8 Security and Privacy Engineering Principles partial match

Secure-engineering principles include bounds-checked coding and safe buffer handling that avoid introducing the flaw.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure-development practices directly prevent introduction of stack buffer overflows.

ID.RA-01 partial match
prevents

Vulnerability scanning can discover stack buffer overflows but does not prevent their introduction.

PR.PS-02 partial match
prevents

Patching eliminates known instances of the weakness after discovery.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing (fuzzing, static analysis) detects stack overflows before release.

A.8.25 Secure development life cycle partial match
prevents

Secure SDLC mandates buffer-safety practices that directly prevent stack overflows.

A.8.26 Application security requirements partial match
prevents

Application security requirements can specify buffer-size and input-validation rules.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure architecture principles include memory-safety and least-privilege stack usage.

A.8.28 Secure coding partial match
prevents

Secure coding standards explicitly forbid unsafe buffer handling that causes CWE-121.

A.8.32 Change management none match
none

Change-management gates can enforce security reviews that catch buffer issues.

Hardening callouts derived

Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (authoritative rows only; rows rated `none` are excluded).

Oracle Linux 8 (1 rule)
  • V-248594 OL 8 must implement address space layout randomization (ASLR) to protect its memory from unauthorized code execution. prevents CWE-121
Oracle Linux 9 (1 rule)
  • V-271452 OL 9 must use a Linux Security Module configured to enforce limits on system services. prevents CWE-121

References