CVE-2025-4144 (GCVE-0-2025-4144)
Vulnerability from cvelistv5 – Published: 2025-05-01 00:50 – Updated: 2025-05-01 15:33
VLAI
EPSS
VEX
Title
PKCE bypass via downgrade attack
Summary
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.
Severity
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2025-05-01 14:30 UTC
CWE
- CWE-287 - Improper Authentication
Assigner
cloudflare
CNA
References
1 reference
Date Public
2025-04-30 16:30
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Browse all ATT&CK techniques and the vulnerabilities related to each.
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