CVE-2026-123272
High
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.
SeverityHigh
CVSS8.0
Exploit probability—
ProductMark3labs Mcp-go
PublishedNov 5, 2026
First seenNov 5, 2026
Weakness typeCWE-346CWE-346
How to fix
Update
- mark3labs mcp-gov1.2.1 or later
Patches
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| mark3labs mcp-go | v0.48.0 ≤ v < v1.2.1 | v1.2.1 |
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