CVE-2025-62800
October 28, 2025
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.
Affected Packages
fastmcp (CONDA):
Affected version(s) >=2.3.4 <2.13.0Fix Suggestion:
Update to version 2.13.0https://github.com/jlowin/fastmcp.git (GITHUB):
Affected version(s) >=v0.1.0 <v2.13.0Fix Suggestion:
Update to version v2.13.0fastmcp (PYTHON):
Affected version(s) >=0.1.0 <2.13.0Fix Suggestion:
Update to version 2.13.0fastmcp (PYTHON):
Affected version(s) >=0.1.0 <2.13.0Fix Suggestion:
Update to version 2.13.0Related Resources (5)
Do you need more information?
Contact UsCVSS v4
Base Score:
5.3
Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
NONE
Privileges Required
NONE
User Interaction
PASSIVE
Vulnerable System Confidentiality
NONE
Vulnerable System Integrity
NONE
Vulnerable System Availability
NONE
Subsequent System Confidentiality
LOW
Subsequent System Integrity
LOW
Subsequent System Availability
NONE
CVSS v3
Base Score:
6.1
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
REQUIRED
Scope
CHANGED
Confidentiality
LOW
Integrity
LOW
Availability
NONE
Weakness Type (CWE)
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
EPSS
Base Score:
0.08
