CVE-2025-4144 : faille critique cloudflare workers-oauth-provider (CVSS 9.8)

PKCE was implemented in the OAuth implementation in workers-oauth-provider that is part of MCP framework https://github.com/cloudflare/workers-mcp . However, it was found that an attacker could cause the check to be skipped. Fixed in: https://github.com/cloudflare/workers-oauth-provider/pull/27 https://github.com/cloudflare/workers-oauth-provider/pull/27 Impact: PKCE is a defense-in-depth mechanism against certain kinds of attacks and was an optional extension in OAuth 2.0 which became required in the OAuth 2.1 draft. (Note that the MCP specification requires OAuth 2.1.). This bug completely bypasses PKCE protection.

Sévérité

Critique (CVSS 9.8)

Vecteur CVSS

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Exploitation active

Non signalée par la CISA

Publication

1 mai 2025

Dernière mise à jour

17 juin 2026

• cloudflare workers-oauth-provider

• Fiche CVE-2025-4144 sur le NVD (NIST)
• github.com/cloudflare/workers-oauth-provider/pull/27