CVE-2025-4144: @cloudflare/workers-oauth-provider PKCE bypass via downgrade attack

May 1, 2025 (updated October 31, 2025)

PKCE was implemented in the OAuth implementation in workers-oauth-provider that is part of MCP framework. However, it was found that an attacker could cause the check to be skipped.

References

github.com/advisories/GHSA-qgp8-v765-qxx9
github.com/cloudflare/workers-oauth-provider
github.com/cloudflare/workers-oauth-provider/pull/27
github.com/cloudflare/workers-oauth-provider/security/advisories/GHSA-qgp8-v765-qxx9
nvd.nist.gov/vuln/detail/CVE-2025-4144

Code Behaviors & Features

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