CVE-2026-124040 CivetWeb through 1.16 HTTP/2 Use-After-Free via Stale Pseudo-Header State

Critical 9.2 Published 6 Nov 2026 Updated 11 Nov 2026

Exploited in the wild: Not known
Fix: None listed

What is CVE-2026-124040?

CVE-2026-124040 is a critical vulnerability in civetweb, published on 6 Nov 2026.

Official description

CivetWeb through 1.16, when built with USE_HTTP2 and enable_http2 on, contains a use-after-free vulnerability in handle_http2() that retains freed :method and :path pointers. Unauthenticated remote attackers can send a later HEADERS frame omitting these pseudo-headers to influence request method or path seen by access rules, or crash the server.

Weakness: CWE-416

Which versions are affected by CVE-2026-124040?

How do I fix CVE-2026-124040?

No fix has been published for CVE-2026-124040 yet. Limit exposure of the affected software until one is available.

Is CVE-2026-124040 being exploited?

There is no known exploitation of CVE-2026-124040 in the wild and no public exploit code.

Public exploit code: 1 proofs of concept on GitHub.

Sources

Also known as AZL-113116, DEBIAN-CVE-2026-124040, GHSA-wj2x-x5pc-4h8r, UBUNTU-CVE-2026-124040.