PUBLISHED DATE: May 1, 2025CVE-2025-4144:
PKCE was implemented in...

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.

Products

• Cloudflare Workers OAuth Provider 0.0.5

Questions to Ask Vendors

1. Can you confirm whether your systems are affected by CVE-2025-4144, and if so, what steps are you currently taking to mitigate this vulnerability?
2. What is your estimated timeline for fully resolving CVE-2025-4144 in your products or services, and how will you communicate updates on this issue to us as your customer?

Recommended Actions

• Check out the advisory links provided below.

References

• http://webappsec.pbworks.com/Insufficient-Authentication
• https://capec.mitre.org/data/definitions/114.html
• https://capec.mitre.org/data/definitions/115.html
• https://capec.mitre.org/data/definitions/151.html
• https://capec.mitre.org/data/definitions/194.html
• https://capec.mitre.org/data/definitions/22.html
• https://capec.mitre.org/data/definitions/57.html
• https://capec.mitre.org/data/definitions/593.html
• https://capec.mitre.org/data/definitions/633.html
• https://capec.mitre.org/data/definitions/650.html
• https://capec.mitre.org/data/definitions/94.html
• https://nvd.nist.gov/vuln/detail/CVE-2025-4144