# HTTP Response Splitting via Non-VCHAR Bytes in cow_http_struct_hd:escape_string/2

Advisory record · `GHSA-w4f7-4cxr-rv3c`

- **Identifiers:** `GHSA-w4f7-4cxr-rv3c` · `CVE-2026-43966` · `EEF-CVE-2026-43966`
- **State:** Confirmed
- **Severity:** CVSS 6.3 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-113](https://cwe.mitre.org/data/definitions/113.html)
- **Tags:** [Other injection](https://agentprime.io/advisories/tag/injection.md)
- **Published:** 8 Jun 2026
- **Updated:** 14 Oct 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 8 Jun 2026, 16:34 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `cowlib` (Hex): affected `>=2.9.0`; no fixed version yet

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 6.3 Medium, CVSS 4.0: `CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N`, from CNA (EEF)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0026, the 17th percentile, on 6 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 15:25 UTC: First seen by agentprime
- 31 Oct 2026, 15:25 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/EEF-CVE-2026-43966)

## Sources

- [GitHub Advisory Database: GHSA-w4f7-4cxr-rv3c](https://github.com/advisories/GHSA-w4f7-4cxr-rv3c)
- [OSV: GHSA-w4f7-4cxr-rv3c](https://osv.dev/vulnerability/GHSA-w4f7-4cxr-rv3c)
- <https://github.com/ninenines/cowboy/commit/f77cb9b5e730e300fffb551db1ba5d1c4ed878ef>
- <https://cna.erlef.org/cves/CVE-2026-43966.html>
- <https://github.com/ninenines/gun/commit/4f35609eb37109b106a863fc9ba83d7ee64e3e42>
- <https://github.com/ninenines/cowlib/commit/a8b793db3d6ffe91d62f81baf41b1dab4cd78fb6>
- <https://github.com/ninenines/cowlib/commit/4401b858f2229abb3ea115c60924f6c77e5f8aa3>
- <https://hex.pm/packages/cowlib>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-w4f7-4cxr-rv3c>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-w4f7-4cxr-rv3c/>. Everything for agents: <https://agentprime.io/llms.txt>.