How severe is CVE-2025-62800?

CVE-2025-62800 has a CVSS 3.x base score of 6.1, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2025-62800 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (16th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2025-62800?

CVE-2025-62800 affects Jlowin Fastmcp. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2025-62800?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2025-62800 have an EU (EUVD) identifier?

Yes. CVE-2025-62800 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-36568.

When was CVE-2025-62800 published?

CVE-2025-62800 was published on 2025-10-28 and last updated on 2026-06-17.

CVE-2025-62800

CVE-2025-62800 is a medium-severity vulnerability in Jlowin Fastmcp with a CVSS 3.x base score of 6.1. 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-79.

Key facts

Severity: Medium (CVSS 3.x base score 6.1)
CVSS v4: 5.3
EPSS exploit prediction: 0% (16th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2025-36568
Weakness: CWE-79
Affected product: Jlowin Fastmcp
Published: 2025-10-28
Last modified: 2026-06-17

Description

FastMCP is the standard framework for building MCP applications. Versions prior to 2.13.0 have a reflected cross-site scripting vulnerability in the OAuth client callback page (oauth_callback.py) where unescaped user-controlled values are inserted into the generated HTML, allowing arbitrary JavaScript execution in the callback server origin. The issue is fixed in version 2.13.0.

Frequently asked questions

What is CVE-2025-62800?: FastMCP is the standard framework for building MCP applications. Versions prior to 2.13.0 have a reflected cross-site scripting vulnerability in the OAuth client callback page (oauth_callback.py) where unescaped user-controlled values are inserted into the generated HTML, allowing arbitrary JavaScript execution in the callback server origin. The issue is fixed in version 2.13.0.
How severe is CVE-2025-62800?: CVE-2025-62800 has a CVSS 3.x base score of 6.1, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2025-62800 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (16th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2025-62800?: CVE-2025-62800 affects Jlowin Fastmcp. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2025-62800?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2025-62800 have an EU (EUVD) identifier?: Yes. CVE-2025-62800 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-36568.
When was CVE-2025-62800 published?: CVE-2025-62800 was published on 2025-10-28 and last updated on 2026-06-17.

References

https://github.com/jlowin/fastmcp/security/advisories/GHSA-mxxr-jv3v-6pgc

Affected products (1)

cpe:2.3:a:jlowin:fastmcp:*:*:*:*:*:*:*:*

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