F5 BIG-IP Stack-Based Buffer Overflow
CVE-2025-53521 is a critical-severity stack-based buffer overflow vulnerability in BIG-IP from F5, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 17.5.1.3, 17.1.3, 16.1.6.1 as the first without the flaw, so updating BIG-IP to one of those releases or later removes the exposure. CISA added it to the Known Exploited Vulnerabilities catalogue on March 27, 2026, which means attacks have been observed in the wild.
Attackers are already exploiting this vulnerability, according to CISA.
What to do
- Update BIG-IP to 17.5.1.3 or 17.1.3 or 16.1.6.1 or 15.1.10.8, whichever matches your release line, or a later version.
- Update Big-ip Access Policy Manager to 15.1.10.8 or 16.1.6.1 or 17.1.3 or 17.5.1.3, whichever matches your release line, or a later version.
- CISA's 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.
- Read the advisory on my.f5.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| F5 | BIG-IP | 17.5.0 up to, but not including, 17.5.1.3; 17.1.0 up to, but not including, 17.1.3; 16.1.0 up to, but not including, 16.1.6.1; 15.1.0 up to, but not including, 15.1.10.8 | 17.5.1.3, 17.1.3, 16.1.6.1, 15.1.10.8 |
| F5 | Big-ip Access Policy Manager | 15.1.0 up to, but not including, 15.1.10.8; 16.1.0 up to, but not including, 16.1.6.1; 17.1.0 up to, but not including, 17.1.3; 17.5.0 up to, but not including, 17.5.1.3 | 15.1.10.8, 16.1.6.1, 17.1.3, 17.5.1.3 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by CNA (f5.com).
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 9.3 | Critical | CNA (f5.com) |
| CVSS 3.1 | 9.8 | Critical | CNA (f5.com) |
Official 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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Stack-based Buffer Overflow
The product writes past the end of a buffer that was allocated on the stack.
How developers prevent this class of flaw
- Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking. D3-SFCV (Stack Frame Canary Validation) from D3FEND discusses canary-based detection in detail.
- Use an abstraction library to abstract away risky APIs. Not a complete solution.
- Implement and perform bounds checking on input.
Timeline
- CVE record published.
- Added to CISA's Known Exploited Vulnerabilities catalogue.
- CISA published its SSVC assessment (exploitation: active, automatable: yes, technical impact: total).
- Deadline for US federal agencies to remediate, set by CISA.
- Record last changed materially (score, affected products, status or references).
References
Advisories
Third-party and government advisories
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-53521US Government Resource
Other vulnerabilities in BIG-IP
- 9.8 Critical severity
F5 BIG-IP APM Heap-based Buffer Overflow Exploited
- 8.8 High severity
- 7.5 High severity
- 8.7 High severity
- 8.7 High severity
- 7.5 High severity
Recent Stack-based Buffer Overflow vulnerabilities
- 7.5 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.5 High severity
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