#VU108849 Inefficient regular expression complexity in koa - CVE-2025-25200

Vulnerability identifier: #VU108849

Vulnerability risk: Critical

CVSSv4.0: 7.7 [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/E:U/U:Red]

CVE-ID: CVE-2025-25200

CWE-ID: CWE-1333

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
koa
Web applications / Other software

Vendor: Koa.js

Description

The vulnerability allows a remote attacker to perform a denial of service (DoS) attack.

The vulnerability exists due Koa uses an evil regex to parse the `X-Forwarded-Proto` and `X-Forwarded-Host` HTTP headers. A remote attacker can pass specially crafted data to the application and perform regular expression denial of service (ReDos) attack.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

koa: before 0.21.2

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External links
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/commit/5054af6e31ffd451a4151a1fe144cef6e5d0d83c
https://github.com/koajs/koa/commit/5f294bb1c7c8d9c61904378d250439a321bffd32
https://github.com/koajs/koa/commit/93fe903fc966635a991bcf890cfc3427d33a1a08
https://github.com/koajs/koa/releases/tag/2.15.4
https://github.com/koajs/koa/security/advisories/GHSA-593f-38f6-jp5m

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.