CVE-2025-4144 — CRITICAL (9.8)

Vulnerability 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.

CVSS Score

9.8

CRITICAL

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

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

NONE

User Interaction

NONE

Scope

UNCHANGED

Confidentiality

HIGH

Integrity

HIGH

Availability

HIGH

Affected Products

Vendor	Product	Versions
Cloudflare	Workers-Oauth-Provider	0.0.5

Related Weaknesses (CWE)

CWE-287

References

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

FAQ

What is CVE-2025-4144?

CVE-2025-4144 is a vulnerability with a CVSS score of 9.8 (CRITICAL). 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...

How severe is CVE-2025-4144?

CVE-2025-4144 has been rated CRITICAL with a CVSS base score of 9.8/10. This is considered a critical vulnerability requiring immediate attention.

Is there a patch for CVE-2025-4144?

Check the references section above for vendor advisories and patch information. Affected products include: Cloudflare Workers-Oauth-Provider.