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.

CVSS v3 6.1 MEDIUM

6.1^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 2.8 / Impact : 2.7

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction REQUIRED

Confidentiality Impact LOW

Integrity Impact LOW

Availability Impact NONE

Scope CHANGED

References

Link	Resource
https://github.com/jlowin/fastmcp/security/advisories/GHSA-mxxr-jv3v-6pgc	Exploit Third Party Advisory
https://github.com/jlowin/fastmcp/security/advisories/GHSA-mxxr-jv3v-6pgc	Exploit Third Party Advisory

Configurations

Configuration 1 (hide)

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

History

07 Nov 2025, 01:49

Type	Values Removed	Values Added
First Time		Jlowin Jlowin fastmcp
CVSS	v2 : ~~unknown~~ v3 : ~~unknown~~	v2 : unknown v3 : 6.1
CPE		cpe:2.3:a:jlowin:fastmcp::::::::
References	~~() https://github.com/jlowin/fastmcp/security/advisories/GHSA-mxxr-jv3v-6pgc -~~	() https://github.com/jlowin/fastmcp/security/advisories/GHSA-mxxr-jv3v-6pgc - Exploit, Third Party Advisory

29 Oct 2025, 16:15

Type	Values Removed	Values Added
References	~~() https://github.com/jlowin/fastmcp/security/advisories/GHSA-mxxr-jv3v-6pgc -~~	() https://github.com/jlowin/fastmcp/security/advisories/GHSA-mxxr-jv3v-6pgc -

28 Oct 2025, 22:15

Type	Values Removed	Values Added
New CVE

Information

Published : 2025-10-28 22:15

Updated : 2025-11-07 01:49

NVD link : CVE-2025-62800

Mitre link : CVE-2025-62800

CVE.ORG link : CVE-2025-62800

JSON object : View

Products Affected

jlowin

fastmcp

CWE

CWE-79

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

{"id": "CVE-2025-62800", "cveTags": [], "metrics": {"cvssMetricV31": [{"type": "Primary", "source": "nvd@nist.gov", "cvssData": {"scope": "CHANGED", "version": "3.1", "baseScore": 6.1, "attackVector": "NETWORK", "baseSeverity": "MEDIUM", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N", "integrityImpact": "LOW", "userInteraction": "REQUIRED", "attackComplexity": "LOW", "availabilityImpact": "NONE", "privilegesRequired": "NONE", "confidentialityImpact": "LOW"}, "impactScore": 2.7, "exploitabilityScore": 2.8}], "cvssMetricV40": [{"type": "Secondary", "source": "security-advisories@github.com", "cvssData": {"Safety": "NOT_DEFINED", "version": "4.0", "Recovery": "NOT_DEFINED", "baseScore": 5.3, "Automatable": "NOT_DEFINED", "attackVector": "NETWORK", "baseSeverity": "MEDIUM", "valueDensity": "NOT_DEFINED", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X", "exploitMaturity": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED", "userInteraction": "PASSIVE", "attackComplexity": "LOW", "attackRequirements": "NONE", "privilegesRequired": "NONE", "subIntegrityImpact": "LOW", "vulnIntegrityImpact": "NONE", "integrityRequirement": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "subAvailabilityImpact": "NONE", "vulnAvailabilityImpact": "NONE", "availabilityRequirement": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "subConfidentialityImpact": "LOW", "vulnConfidentialityImpact": "NONE", "confidentialityRequirement": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED"}}]}, "published": "2025-10-28T22:15:36.983", "references": [{"url": "https://github.com/jlowin/fastmcp/security/advisories/GHSA-mxxr-jv3v-6pgc", "tags": ["Exploit", "Third Party Advisory"], "source": "security-advisories@github.com"}, {"url": "https://github.com/jlowin/fastmcp/security/advisories/GHSA-mxxr-jv3v-6pgc", "tags": ["Exploit", "Third Party Advisory"], "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0"}], "vulnStatus": "Analyzed", "weaknesses": [{"type": "Secondary", "source": "security-advisories@github.com", "description": [{"lang": "en", "value": "CWE-79"}]}], "descriptions": [{"lang": "en", "value": "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."}], "lastModified": "2025-11-07T01:49:53.133", "configurations": [{"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:a:jlowin:fastmcp:*:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "938DF638-7486-4DDB-A950-1A16D8FCCEA1", "versionEndExcluding": "2.13.0"}], "operator": "OR"}]}], "sourceIdentifier": "security-advisories@github.com"}