AdvisoriesToolsStatsChecklistSubmitGet the email
← All advisories
CVE-2026-123272highSecret exposure2026-11-05

CVE-2026-123272: Mark3labs mcp-go before v1.2.1 contains an improper validation vulnerability in OAuthHandler.fetchServerMetadata that allows malicious MCP servers to obtain tok

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.

01.

What it is

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.

02.

How to check

  1. Compare your installed version with the range above (command below).
03.

How to fix

    04.

    Sources

    More advisories for this tool
    The weekly email

    One email a week. Only what changed.

    Every new security hole in AI coding tools, MCP servers, app builders and the stacks they generate (Next.js, Supabase, Node, PHP), each with how to check your app and the fix. No roundups of things you already read.

    Free, one email a week. Read the latest issue first if you like. One-click unsubscribe in every email. We never sell or share addresses.