SecuriTricks - CVE-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.

Product(s) Impacted

Vendor	Product	Versions
Cloudflare	Workers Oauth Provider	*

Weaknesses

Common security weaknesses mapped to this vulnerability.

CWE-287

Improper Authentication

When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.

*CPE(s)

Affected systems and software identified for this CVE.

Type	Vendor	Product	Version	Update	Edition	Language	Software Edition	Target Software	Target Hardware	Other Information
a	cloudflare	workers_oauth_provider	/	/	/	/	/	/	/	/

References

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

CVSS Score

5.3 / 10

CVSS Data - 4.0

Attack Vector: NETWORK
Attack Complexity: LOW
Attack Requirements: NONE
Privileges Required: NONE
User Interaction: PASSIVE
Scope:
Confidentiality Impact: NONE
Integrity Impact: LOW
Availability Impact: NONE
Exploit Maturity: NOT_DEFINED

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:Amber

View Vector String

Timeline

Published: May 1, 2025, 1:15 a.m.
Last Modified: May 1, 2025, 1:15 a.m.

Status : Received

CVE has been recently published to the CVE List and has been received by the NVD.

More info

Source

cna@cloudflare.com

CVE-2025-4144