Medium severity6.1NVD Advisory· Published Oct 28, 2025· Updated Jun 17, 2026

CVE-2025-62800

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.

AI Insight

LLM-synthesized narrative grounded in this CVE's description and references.

Affected packages

Versions sourced from the GitHub Security Advisory.

Package	Affected versions	Patched versions
fastmcpPyPI	< 2.13.0	2.13.0

Affected products

Jlowin/Fastmcp2 versions
cpe:2.3:a:jlowin:fastmcp:*:*:*:*:*:*:*:*+ 1 more
- cpe:2.3:a:jlowin:fastmcp:*:*:*:*:*:*:*:*range: <2.13.0
- (no CPE)range: < 2.13.0
ghsa-coords
pkg:pypi/fastmcp
Range: < 2.13.0

Patches

Vulnerability mechanics

References

github.com/jlowin/fastmcp/security/advisories/GHSA-mxxr-jv3v-6pgcnvdExploitThird Party AdvisoryWEB
github.com/advisories/GHSA-mxxr-jv3v-6pgcghsaADVISORY
nvd.nist.gov/vuln/detail/CVE-2025-62800ghsaADVISORY
github.com/jlowin/fastmcp/commit/2a20f54617a37213ed83894a8c2f0ac38a2e83a3ghsaWEB
github.com/jlowin/fastmcp/pull/2090ghsaWEB

News mentions

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cvss	0.397
epss	0.000
exploit	0.000
kev	0.000
patch	-0.070
ransomware	0.000