Use After Free in Civetweb
CVE-2026-124040
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.
Vulnerability class: Use-After-Free
Published · last modified .
CVSS v3 metric
CVSS v3 base score 8.1 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H.
EPSS exploit prediction
No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.
Affected products
Weakness classification (CWE)
References
- github.com/civetweb/civetweb (product)
- github.com/civetweb/civetweb/blob/v1.16/src/http2.inl (technical-description)
- GitHub Issue #1379 (issue-tracking)
- VulnCheck Advisory: CivetWeb through 1.16 HTTP/2 Use-After-Free via Stale Pseudo-Header State (third-party-advisory)
Frequently asked questions
- What is CVE-2026-124040?
- CVE-2026-124040 is a high-severity vulnerability in Civetweb, classified under Use After Free. CVSS score: 8.1/10. Published 2026-11-06.
- How severe is CVE-2026-124040?
- High severity. CVSS v3 base score is 8.1 out of 10.