---
title: "CVE-2025-25200: Inefficient Regular Expression Complexity in koa"
url: https://erroneo.us/security/cve/CVE-2025-25200/
description: "CVE-2025-25200 (koa (npm)): Koa is expressive middleware for Node.js using ES2017 async functions. Prior to versions 0.21.2, 1.7.1, 2.15.4, and…"
type: vulnerability-record
section: "Security Digest"
date_published: 2025-02-12
date_modified: 2025-02-12
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2025-25200"
kev: false
cvss: 9.2
epss: 0.00841
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2025-25200: Inefficient Regular Expression Complexity in koa

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.8% , percentile 57: FIRST’s model estimates a 0.8% chance of exploitation activity in the next 30 days, higher than 57% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes koa (npm) >= 2.0.0, < 2.15.4, fixed in 2.15.4 ; koa (npm) >= 3.0.0-alpha.0, < 3.0.0-alpha.3, fixed in 3.0.0-alpha.3 ; koa (npm) >= 1.0.0, < 1.7.1, fixed in 1.7.1 ; koa (npm) < 0.21.2, fixed in 0.21.2 . Check your lockfile, including transitive dependencies.

## What it is

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.

## Affected packages

- npm `koa` >= 2.0.0, < 2.15.4 → fixed: 2.15.4
- npm `koa` >= 3.0.0-alpha.0, < 3.0.0-alpha.3 → fixed: 3.0.0-alpha.3
- npm `koa` >= 1.0.0, < 1.7.1 → fixed: 1.7.1
- npm `koa` < 0.21.2 → fixed: 0.21.2

## Affected products (CVE record)

- koajs koa: < 0.21.2, >= 1.0.0, < 1.7.1, >= 2.0.0-alpha.1, < 2.15.4, >= 3.0.0-alpha.0, < < 3.0.0-alpha.3

## Severity

- GitHub_M CVSS 4.0: 9.2 `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`
- GitHub CVSS 4.0: 9.2 `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`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none , automatable no , technical impact partial .
- FIRST EPSS (model of 2026-10-21): 0.84% probability of exploitation activity in the next 30 days; percentile 57.

## Sources

- [GitHub Advisory GHSA-593f-38f6-jp5m](https://github.com/advisories/GHSA-593f-38f6-jp5m)
- [CVE.org record CVE-2025-25200](https://www.cve.org/CVERecord?id=CVE-2025-25200)
- [NVD entry CVE-2025-25200](https://nvd.nist.gov/vuln/detail/CVE-2025-25200)
- [github.com](https://github.com/koajs/koa/security/advisories/GHSA-593f-38f6-jp5m)
- [github.com](https://github.com/koajs/koa/commit/5054af6e31ffd451a4151a1fe144cef6e5d0d83c)
- [github.com](https://github.com/koajs/koa/commit/5f294bb1c7c8d9c61904378d250439a321bffd32)
- [github.com](https://github.com/koajs/koa/commit/93fe903fc966635a991bcf890cfc3427d33a1a08)
- [github.com](https://github.com/koajs/koa/blob/master/lib/request.js#L259)
- [github.com](https://github.com/koajs/koa/blob/master/lib/request.js#L404)
- [github.com](https://github.com/koajs/koa/releases/tag/2.15.4)

---
Source page: https://erroneo.us/security/cve/CVE-2025-25200/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt