CVE-2026-123272
Published:November 05, 2026
Updated:November 10, 2026
Mark3labs mcp-go before v1.2.1 contains an improper validation vulnerability in OAuthHandler.fetchServerMetadata that allows malicious MCP servers to obtain tokens for other resources by declaring arbitrary resources in well-known metadata. Attackers can declare a different MCP server as the RFC 8707 resource indicator, causing the authorization server to mint tokens the attacker replays against that resource.
Affected Packages
https://github.com/mark3labs/mcp-go.git (GITHUB):
Affected version(s) >=v0.48.0 <v1.2.1Fix Suggestion:
Update to version v1.2.1github.com/mark3labs/mcp-go (GO):
Affected version(s) >=v0.48.0 <v1.2.1 || >=v0.54.1 <v1.2.1Fix Suggestion:
Update to version v1.2.1Related Resources (9)
Do you need more information?
Contact UsCVSS v4
Base Score:
5
Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
PRESENT
Privileges Required
NONE
User Interaction
ACTIVE
Vulnerable System Confidentiality
NONE
Vulnerable System Integrity
NONE
Vulnerable System Availability
NONE
Subsequent System Confidentiality
HIGH
Subsequent System Integrity
HIGH
Subsequent System Availability
NONE
CVSS v3
Base Score:
8
Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
NONE
User Interaction
REQUIRED
Scope
CHANGED
Confidentiality
HIGH
Integrity
HIGH
Availability
NONE
Weakness Type (CWE)
Origin Validation Error
EPSS
Base Score:
0.20