How severe is CVE-2025-4144?

CVE-2025-4144 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2025-4144 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (39th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2025-4144?

CVE-2025-4144 affects Cloudflare Workers-oauth-provider. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2025-4144?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

Does CVE-2025-4144 have an EU (EUVD) identifier?

Yes. CVE-2025-4144 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-12788.

When was CVE-2025-4144 published?

CVE-2025-4144 was published on 2025-05-01 and last updated on 2026-06-17.

CVE-2025-4144

CVE-2025-4144 is a critical-severity vulnerability in Cloudflare Workers-oauth-provider with a CVSS 3.x base score of 9.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-287.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v4: 5.3
EPSS exploit prediction: 0% (39th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2025-12788
Weakness: CWE-287
Affected product: Cloudflare Workers-oauth-provider
Published: 2025-05-01
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2025-4144?: 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.
How severe is CVE-2025-4144?: CVE-2025-4144 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2025-4144 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (39th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2025-4144?: CVE-2025-4144 affects Cloudflare Workers-oauth-provider. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2025-4144?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
Does CVE-2025-4144 have an EU (EUVD) identifier?: Yes. CVE-2025-4144 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-12788.
When was CVE-2025-4144 published?: CVE-2025-4144 was published on 2025-05-01 and last updated on 2026-06-17.

References

https://github.com/cloudflare/workers-oauth-provider/pull/27

Affected products (1)

cpe:2.3:a:cloudflare:workers-oauth-provider:0.0.5:*:*:*:*:*:*:*

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