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

Source: https://junglewise.ai/threats/cve-2026-42409-f5-big-ip-dos-via-http-2-irule-redirection  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-13. Updated: 2026-06-23  
License: CC BY 4.0 with a link back

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](https://junglewise.ai/threats/technologies/big-ip), [F5 BIG-IP Advanced WAF](https://junglewise.ai/threats/technologies/big-ip-advanced-waf), [F5 Big-Ip Access Policy Manager](https://junglewise.ai/threats/technologies/big-ip-access-policy-manager), [F5 Big-Ip Advanced Firewall Manager](https://junglewise.ai/threats/technologies/big-ip-advanced-firewall-manager), [F5 Big-Ip Local Traffic Manager](https://junglewise.ai/threats/technologies/big-ip-local-traffic-manager). Vendors: [F5](https://junglewise.ai/threats/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

- [https://my.f5.com/manage/s/article/K000159034](https://my.f5.com/manage/s/article/K000159034)

## Related threats

- [F5 BIG-IP privilege escalation in TMUI](https://junglewise.ai/threats/cve-2026-66842-f5-big-ip-privilege-escalation-in-tmui)
- [F5 BIG-IP Configuration utility error message spoofing](https://junglewise.ai/threats/cve-2026-63020-f5-big-ip-configuration-utility-error-message-spoofing)
- [F5 BIG-IP denial of service in HTTP/2 profile memory management](https://junglewise.ai/threats/cve-2026-59762-f5-big-ip-denial-of-service-in-http-2-profile-memory-management)
- [F5 BIG-IP and BIG-IQ incorrect permission assignment in tmsh and iControl REST](https://junglewise.ai/threats/cve-2026-42937-f5-big-ip-and-big-iq-incorrect-permission-assignment-in-tmsh-and)
- [F5 BIG-IP Appliance mode restriction bypass via path traversal](https://junglewise.ai/threats/cve-2026-42930-f5-big-ip-appliance-mode-restriction-bypass-via-path-traversal)