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CVE-2025-53521

9.8, critical Known exploited

F5 BIG-IP Stack-Based Buffer Overflow Vulnerability

NVD (opens in a new tab) CVE.org (opens in a new tab) CISA KEV catalogue (opens in a new tab)
CVSS
9.8, critical critical CVSS v3.1
EPSS, next 30 days
2% higher than 82.9% of scored CVEs
Exploitation
Confirmed in the wild
Published
15 Oct 2025a year ago

Known exploited

CISA added this to the Known Exploited Vulnerabilities Catalog on 27 Mar 2026. US federal agencies had to remediate by 30 Mar 2026, a deadline that has passed.

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.

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.

Details

Vendor
F5
Product
BIG-IP
Weakness
CWE-121 (opens in a new tab)
Status
Analyzed
Updated
8 Oct 2026
Assigner
f5sirt@f5.com

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

References 2

Advisories 1

Other references 1

The kind is read from NVD's tags where present and from the shape of the URL otherwise, so treat it as a hint.

Other F5 CVEs

Every F5 CVE we hold

Same vendor in what we hold, not a known link between the flaws.

  • CVE-2026-94127 F5 BIG-IP APM Heap-based Buffer Overflow Vulnerability KEV EPSS 2% 9.8, critical
  • CVE-2023-46747 F5 BIG-IP Configuration Utility Authentication Bypass Vulnerability KEV EPSS 97% 9.8, critical
  • CVE-2023-46748 F5 BIG-IP Configuration Utility SQL Injection Vulnerability KEV EPSS 4% 8.8, high
  • CVE-2022-1388 F5 BIG-IP Missing Authentication Vulnerability KEV EPSS 100% 9.8, critical
  • CVE-2021-22986 F5 BIG-IP and BIG-IQ Centralized Management iControl REST Remote Code Execution Vulnerability KEV EPSS 100% 9.8, critical
  • CVE-2021-22991 F5 BIG-IP Traffic Management Microkernel Buffer Overflow KEV EPSS 61% 9.8, critical
  • CVE-2020-5902 F5 BIG-IP Traffic Management User Interface (TMUI) Remote Code Execution Vulnerability KEV EPSS 100% 9.8, critical
  • CVE-2026-104939 Description NGINX Ingress Controller has a vulnerability when implementing an externalAuth policy for ingress EPSS 0.4% 7.5, high

Beyond this page

Is CVE-2025-53521 in your network?

This page tells you how dangerous CVE-2025-53521 is out there. Whether it sits on one of your devices, only a scan of your own network can tell. That is what our systems do, every day, for the companies we protect.

CVE-2025-53521 is in the CISA catalogue of exploited vulnerabilities: attackers are already exploiting it.

  • EXYS7600 OCELOT

    Find it before attackers do

    Ocelot scans your network on a schedule and reports every vulnerability it finds by its CVE identifier, with its CVSS score and how many of your hosts are affected. A finding like CVE-2025-53521 comes with the devices to patch.

    Learn more about EXYS7600 OCELOT

  • EXYS7950 KONDRA

    Detect it if it's exploited

    Until the patch is applied, Kondra monitors your network, events and endpoints in real time. It keeps an inventory of the software installed on every endpoint, and its anomaly detection rules flag what an attacker does once inside.

    Learn more about EXYS7950 KONDRA
Check your exposure

Assembled from the NVD 2.0 API, the CISA Known Exploited Vulnerabilities Catalog and FIRST EPSS. Scores are as of our last collection on 17 Oct 2026, not the live upstream state.