CVE-2025-4144CRITICAL 9.8EPSS p38.3%

CVE-2025-4144CVE-2025-4144

Description

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.

Scoring

CVSS 3.19.8 (CRITICAL)
VectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS0.49% probability of exploitation · percentile 38.3% · 2026-06-19T12:03:05Z
Published2025-05-01
Last modified2025-05-12

Underlying weaknesses· 1

CWE-287

References

  1. https://github.com/cloudflare/workers-oauth-provider/pull/27

1

TypeTargetConfidenceTier
WeaknessImproper Authenticationcwe-2870%live

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Sourced from NVD + FIRST.org EPSS. Curated for EU compliance use cases by Adam Lundqvist, Founder at SQUR.