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CVE-2025-4144

PKCE bypass via downgrade attack

Published: May 1, 2025Updated: May 12, 2025 Sources: CVE List NVD GHSACWE-287
9.8CRITICAL
NVD MITRE
EPSS Score
0.5%
Top 61.7%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available

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.

No summary for this CVE yet.

CVSS Vector Breakdown

AV:NAC:LPR:NUI:NS:UC:HI:HA:H
Exploitability
AV:NAttack Vector
Network
AC:LAttack Complexity
Low
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:HConfidentiality
High
I:HIntegrity
High
A:HAvailability
High
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Weaknesses

CWE-287NVD-CWE-noinfo

Affected Products

workers-oauth-providercloudflare
SaaS
Security Products / secure-gateway-vpn
@cloudflare/workers-oauth-providernpmOSS Libraries
cloudflarecommercialUSSecurity Productsaka warp, octorpki, quiche
npmpackage-ecosystemOSS Libraries

Exploitability

Official Patch Available
No detection template yetWe can run the check for you — a free external exposure review, no install. Check my exposure

Attack Graph

Products CVE Techniques Tactics

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MITRE ATT&CK

2 techniques
Initial Access
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References

https://github.com/cloudflare/workers-oauth-provider/pull/27
github.com
https://github.com/cloudflare/workers-oauth-provider/security/advisories/GHSA-qgp8-v765-qxx9
github.com
https://nvd.nist.gov/vuln/detail/CVE-2025-4144
nvd.nist.gov
and 1 more references View all →

Timeline

Published
May 1, 2025
Last Updated
May 12, 2025

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