CVE-2025-4144 – @cloudflare/workers-oauth-provider

Package

Manager: npm
Name: @cloudflare/workers-oauth-provider
Vulnerable Version: >=0 <0.0.5

Severity

Level: Medium

CVSS v3.1: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N/E:U/RL:O/RC:C

CVSS v4.0: 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

EPSS: 0.00075 pctl0.23143

Details

@cloudflare/workers-oauth-provider 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. ### 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. ### Patches Fixed in: https://github.com/cloudflare/workers-oauth-provider/pull/27 We patched up the vulnerabilities in the latest version, v 0.0.5 of the Workers OAuth provider (https://www.npmjs.com/package/@cloudflare/workers-oauth-provider). You'll need to update your MCP servers to use that version to resolve the vulnerability. ### Workarounds None

Metadata

Created: 2025-05-01T17:01:42Z
Modified: 2025-05-01T17:01:42Z
Source: https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2025/05/GHSA-qgp8-v765-qxx9/GHSA-qgp8-v765-qxx9.json
CWE IDs: ["CWE-287"]
Alternative ID: GHSA-qgp8-v765-qxx9
Finding: F039
Auto approve: 1