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


- **Severity:** Critical 9.2 (`CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 6 Nov 2026
- **Updated:** 11 Nov 2026
- **Also known as:** AZL-113116, DEBIAN-CVE-2026-124040, GHSA-wj2x-x5pc-4h8r, UBUNTU-CVE-2026-124040

## 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 (Use After Free)

## 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:

- https://github.com/zeetee1235/CVE-2026-124040 (github_poc): https://github.com/zeetee1235/CVE-2026-124040

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-124040 and fix it if it is affected.

What it is: CVE-2026-124040 is a critical vulnerability in civetweb, published on 6 Nov 2026. 
Exploitation: There is no known exploitation of CVE-2026-124040 in the wild and no public exploit code.

Affected product: civetweb. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-124040/ (Markdown: https://insights.sbomify.com/CVE-2026-124040/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-124040
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-124040
- OSV: https://osv.dev/vulnerability/CVE-2026-124040

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-124040/
Summaries are generated and may contain mistakes; the official description above is the record.