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Advisories

mcp-go before v1.2.1 Origin Validation Error via Unvalidated Well-Known Protected Resource Metadata

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Severity
medium
Date
Affecting

  • mcp-go >= v0.48.0, < v1.2.1

CWE
  • CWE-346 Origin Validation Error
CVSS
5.1
CVSS V4 Vector
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N
Credit
Theodoros Lampropoulos, Ed Zynda (ezynda3)
Description
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.

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