CVE-2026-123272mediumCWE-346

CVE-2026-123272: medium-severity vulnerability in mark3labs mcp-go

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

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13Vexday Risk Score

No sign of exploitation. No public exploitation artifact known so far.

ssvc Trackcvss 5.1epss 0.2%
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.
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
Affected products
mark3labs · mcp-go
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