# HTTP Response Splitting (Early Hints) in Puma

Advisory record · `GHSA-33vf-4xgg-9r58`

- **Identifiers:** `GHSA-33vf-4xgg-9r58` · `CVE-2020-5249`
- **State:** Confirmed
- **Severity:** CVSS 6.5 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-74](https://cwe.mitre.org/data/definitions/74.html) · [CWE-113](https://cwe.mitre.org/data/definitions/113.html)
- **Tags:** [Other injection](https://agentprime.io/advisories/tag/injection.md)
- **Published:** 3 Mar 2020
- **Updated:** 4 Feb 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 3 Mar 2020, 23:33 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `puma` (RubyGems): affected `<3.12.4 || >=4.0.0, <4.3.3`; fixed in `3.12.4`, `4.3.3`

## 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

- 6.5 Medium, CVSS 3.1: `CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:L`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.016, the 75th percentile, on 10 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 28 Feb 2020, 19:51 UTC: [Published by the maintainers as a GitHub repository advisory](https://github.com/puma/puma/security/advisories/GHSA-33vf-4xgg-9r58)

## Sources

- [GitHub Advisory Database: GHSA-33vf-4xgg-9r58](https://github.com/advisories/GHSA-33vf-4xgg-9r58)
- [OSV: GHSA-33vf-4xgg-9r58](https://osv.dev/vulnerability/GHSA-33vf-4xgg-9r58)
- <https://github.com/puma/puma/security/advisories/GHSA-33vf-4xgg-9r58>
- <https://github.com/puma/puma/security/advisories/GHSA-84j7-475p-hp8v>
- <https://nvd.nist.gov/vuln/detail/CVE-2020-5249>
- <https://github.com/puma/puma/commit/c22712fc93284a45a93f9ad7023888f3a65524f3>
- <https://github.com/puma/puma>
- <https://github.com/rubysec/ruby-advisory-db/blob/master/gems/puma/CVE-2020-5249.yml>
- <https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/BMJ3CGZ3DLBJ5WUUKMI5ZFXFJQMXJZIK>
- <https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/DIHVO3CQMU7BZC7FCTSRJ33YDNS3GFPK>
- <https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/NJ3LL5F5QADB6LM46GXZETREAKZMQNRD>
- <https://owasp.org/www-community/attacks/HTTP_Response_Splitting>

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-33vf-4xgg-9r58>, 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-33vf-4xgg-9r58/>. Everything for agents: <https://agentprime.io/llms.txt>.