Is CVE-2026-42920 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-42920 being exploited in the wild.

How severe is CVE-2026-42920?

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 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 Application Security 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-2026-42920?

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-2026-42920 attacked?

It is attacked over the network, in a network appliance.

Am I affected by CVE-2026-42920?

Check whether you run F5 BIG-IP, F5 Big-Ip Access Policy Manager, F5 Big-Ip Advanced Firewall 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.

CVE-2026-42920: F5 BIG-IP DoS in TMM via Client SSL Dynamic Record Sizing

CVE-2026-42920 · Severity: high · CVSS 7.5 · Published 2026-05-13

F5 BIG-IP networking devices are susceptible to a denial-of-service vulnerability when processing specific types of encrypted traffic. An attacker can send specially crafted network data to a virtual server, causing the core traffic management component to crash. This results in a complete interruption of network services and application delivery managed by the affected device.

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

Quick answers

Is CVE-2026-42920 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-42920 being exploited in the wild.
How severe is CVE-2026-42920?: 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 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 Application Security 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-2026-42920?: 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-2026-42920 attacked?: It is attacked over the network, in a network appliance.
Am I affected by CVE-2026-42920?: Check whether you run F5 BIG-IP, F5 Big-Ip Access Policy Manager, F5 Big-Ip Advanced Firewall 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

A vulnerability classified as an infinite loop (CWE-835) exists in the F5 BIG-IP Traffic Management Microkernel (TMM). The issue is triggered when a Client SSL profile is configured with 'Allow Dynamic Record Sizing' on a UDP-based virtual server. An unauthenticated remote attacker can send undisclosed network traffic that causes TMM to terminate, leading to a denial-of-service (DoS) condition. The vulnerability affects multiple BIG-IP modules including LTM, APM, AFM, and ASM across versions 16.1.x, 17.5.x, and 21.0.0. F5 has provided mitigation guidance in advisory K000160901.

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 Application Security Manager 16.1.0 - 16.1.6, 17.5.0 - 17.5.1, 21.0.0

Timeline

2026-05-13: advisory: Initial publication of the vulnerability advisory

References

https://my.f5.com/manage/s/article/K000160901

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