CVE-2026-42409: F5 BIG-IP DoS via HTTP/2 iRule redirection

CVE-2026-42409 · Severity: high · CVSS 7.5 · Published 2026-05-13

F5 BIG-IP devices, which manage and secure corporate web traffic, are vulnerable to a flaw that can cause the system to crash. An attacker can send specifically crafted web requests to a server configured with certain redirection rules, leading to a complete service outage. This disrupts network operations and prevents legitimate users from accessing protected applications.

Technologies: F5 BIG-IP, F5 BIG-IP Advanced WAF, F5 Big-Ip Access Policy Manager, F5 Big-Ip Advanced Firewall Manager, F5 Big-Ip Local Traffic Manager. Vendors: F5.

Quick answers

Is CVE-2026-42409 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-42409 being exploited in the wild.
How severe is CVE-2026-42409?
High severity, with a CVSS score of 7.5, published 13 May 2026.
Which products and versions are affected?
F5 BIG-IP Undisclosed (EoTS versions excluded); F5 BIG-IP Advanced WAF 16.1.0 - 16.1.6, 17.5.0 - 17.5.1, 21.0.0; F5 Big-Ip Access Policy Manager 16.1.0 - 16.1.6, 17.5.0 - 17.5.1, 21.0.0; F5 Big-Ip Advanced Firewall Manager 16.1.0 - 16.1.6, 17.5.0 - 17.5.1, 21.0.0; and 1 more.
Is there a fix for CVE-2026-42409?
No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-42409 attacked?
It is attacked over the network, in a network appliance.
Am I affected by CVE-2026-42409?
Check whether you run F5 BIG-IP, F5 BIG-IP Advanced WAF, F5 Big-Ip Access Policy Manager or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

This vulnerability is a NULL pointer dereference (CWE-476) within the Traffic Management Microkernel (TMM) of F5 BIG-IP. It occurs when a virtual server is configured with both an HTTP/2 profile and an iRule that utilizes the 'HTTP::redirect' or 'HTTP::respond' commands. An unauthenticated remote attacker can exploit this by sending undisclosed HTTP/2 requests that trigger the flaw during the redirection or response logic, leading to a TMM process termination and a denial-of-service (DoS) condition. The issue affects multiple BIG-IP modules including LTM, APM, and Advanced WAF across versions 16.x and 17.x.

Affected products

  • F5 BIG-IP Access Policy Manager 16.1.0 - 16.1.6, 17.5.0 - 17.5.1, 21.0.0
  • F5 BIG-IP Advanced Firewall Manager 16.1.0 - 16.1.6, 17.5.0 - 17.5.1, 21.0.0
  • F5 BIG-IP Local Traffic Manager 16.1.0 - 16.1.6, 17.5.0 - 17.5.1, 21.0.0
  • F5 BIG-IP Advanced WAF 16.1.0 - 16.1.6, 17.5.0 - 17.5.1, 21.0.0

Timeline

  • 2026-05-13: disclosed: Initial publication of the vulnerability advisory.

References

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