CVSS 4.0
9.2 criticalCVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:NCVE-2026-124040 CivetWeb through 1.16 HTTP/2 Use-After-Free via Stale Pseudo-Header State
Critical (9.2) in civetweb civetweb. EPSS 0.5% estimated probability of exploitation activity in the next 30 days.
On this page
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.
Severity
CVSS 3.1
8.1 highCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H- EPSS
- 0.5% estimated probability of exploitation activity in the next 30 days; 44th percentile. Scored 2026-11-13. A forecast for this CVE across the internet, not for your own systems.
- CISA's assessment (SSVC)
- Exploitation: none · Automatable: no · Technical impact: total, assessed 2026-11-11. From CISA's Vulnrichment in the CVE List: whether it is exploited, whether exploiting it can be automated, and how much control it gives.
- CWE
- CWE-416 Use After Free
- Published
- Modified
- Assigned by
- VulnCheck (CNA)
- NVD analysis
- Deferred: the NVD does not plan to analyze it
- Record from
- the NVD, synced
Ask an AI about this CVE
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Explain CVE-2026-124040 for an engineer deciding whether to act. Use https://cve.bz/api/public/cves/CVE-2026-124040?via=ask-ai-copy and https://cve.bz/cve/CVE-2026-124040?via=ask-ai-copy as the source of truth: what is affected and which versions fix it, whether it is in CISA KEV, public exploits, and its EPSS (an internet-wide 30-day estimate of exploitation activity, not a forecast for my systems). If they give no fixed versions, use the CVE record https://cveawg.mitre.org/api/cve/CVE-2026-124040 or the vendor advisory, not third-party mirrors. Tell me how to check whether I am affected and how to verify a fix. Cite the sources and say where they are uncertain.Opens a third-party assistant; its answer is its own, not cve.bz's. The prompt holds only this CVE's id and public links.
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Affected
Versions
From the CNA's record in the CVE List.
| Product | Affected |
|---|---|
| civetweb | through 1.16 |
Linux distributions
| Distribution | Release | Package | Fixed in | Advisory |
|---|---|---|---|---|
| Debian | 12, 13, 14 | civetweb | no fix listed | DEBIAN-CVE-2026-124040 |
| Ubuntu | 24.04:LTS, 26.04:LTS, 26.10 and 1 more | civetweb | no fix listed | UBUNTU-CVE-2026-124040 |
| Azure Linux | 3 | ceph | no fix listed | AZL-113116 |
From the distributions' data via OSV.dev: the Debian Security Tracker; Ubuntu Security Notices © Canonical Ltd., CC BY-SA 4.0; Microsoft's Azure Linux vulnerability data, MIT. Modified: reformatted and linked to CVE records. Credits. On the distributions' own pages: Debian · Ubuntu.
GitHub PoC (unverified)
Repositories on GitHub named after this CVE. Nobody has checked them and they are not scanned: some hold a working proof of concept, some nothing useful, and some malware made to look like one. Read the code before you run any of it.
- zeetee1235/CVE-2026-124040 0 stars, Python, created