High severity8.0NVD Advisory· Published Nov 5, 2026· Updated Nov 5, 2026
CVE-2026-123272
CVE-2026-123272
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.
Affected products
1Patches
Vulnerability mechanics
References
6- github.com/mark3labs/mcp-go/blob/4cb0d2015f24b669726fd8e5e53fc8c6d3f57abf/client/transport/oauth.gonvd
- github.com/mark3labs/mcp-go/commit/90d247ed8d45cbb7d71d9a95e112789b78760443nvd
- github.com/mark3labs/mcp-go/pull/1053nvd
- github.com/mark3labs/mcp-go/releases/tag/v1.2.1nvd
- github.com/mark3labs/mcp-go/security/advisories/GHSA-xf6j-693p-wqxxnvd
- www.vulncheck.com/advisories/mcp-go-before-1.2.1-origin-validation-error-via-unvalidated-well-known-protected-resource-metadatanvd
News mentions
0No linked articles in our index yet.