CVE-2025-4144: PKCE was implemented in the OAuth implementation in workers-oauth-provider that is part of MCP framework http

This month

CRITICAL 9.8REMOTEDOWNGRADE

CVE-2025-4144 is a critical-severity flaw (CVSS 9.8) affecting workers-oauth-provider. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 an

Why this priority

Critical severity
Remotely exploitable, no login, no user action

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.6% (top 53%)
CISA exploited list	No
Weakness	CWE-287
Published	2025-05-01
Last modified	2026-06-17

Publisher (CNA): Cloudflare, Inc. · Vendor: cloudflare

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2025-05-01 01:15 UTCPublished CVE record published
2026-06-17 09:32 UTCUpdated Record last modified

cloudflare workers-oauth-provider DOWNGRADE

Affected: 0.0.5

Fixed in: no fixed release known

Safe to downgrade to: a release before 0.0.5

1. Check installed version

apt-cache policy workers-oauth-provider || rpm -q workers-oauth-provider || workers-oauth-provider --version

2. No fixed release: DOWNGRADE to a release before 0.0.5 (Debian / Ubuntu)

apt-cache madison workers-oauth-provider sudo apt install workers-oauth-provider=<VERSION_BEFORE_0.0.5> sudo apt-mark hold workers-oauth-provider

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list workers-oauth-provider sudo dnf downgrade workers-oauth-provider-<VERSION_BEFORE_0.0.5> sudo dnf versionlock add workers-oauth-provider

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2025-4144?

workers-oauth-provider: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2025-4144 being exploited?

CVE-2025-4144 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2025-4144 affect?

CVE-2025-4144 affects workers-oauth-provider. Severity is critical (CVSS 9.8). 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:

How urgent is CVE-2025-4144?

Priority 51/100. Critical severity; Remotely exploitable, no login, no user action

Software pages

GitHub vulnerabilities · Cloudflare vulnerabilities

Related CVEs

CVE-2025-4143 MEDIUM 6.1 DOWNGRADE The OAuth implementation in workers-oauth-provider that is part of MCP framework https://github.com/cloudflar

References

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