CVE-2026-123272

8 HIGHpublic exploit available

Published 2026-11-05 · Updated 2026-11-05

AI analysis for this CVE has not been generated yet. Raw NVD data is shown below.

NVD 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.

CVSS vector

CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:N

Weaknesses

CWE-346

Public exploit & PoC references

https://github.com/mark3labs/mcp-go/blob/4cb0d2015f24b669726fd8e5e53fc8c6d3f57abf/client/transport/oauth.go#L799-L821
https://github.com/mark3labs/mcp-go/commit/90d247ed8d45cbb7d71d9a95e112789b78760443
https://github.com/mark3labs/mcp-go/pull/1053
https://github.com/mark3labs/mcp-go/releases/tag/v1.2.1
https://github.com/mark3labs/mcp-go/security/advisories/GHSA-xf6j-693p-wqxx

All references

https://github.com/mark3labs/mcp-go/blob/4cb0d2015f24b669726fd8e5e53fc8c6d3f57abf/client/transport/oauth.go#L799-L821
https://github.com/mark3labs/mcp-go/commit/90d247ed8d45cbb7d71d9a95e112789b78760443
https://github.com/mark3labs/mcp-go/pull/1053
https://github.com/mark3labs/mcp-go/releases/tag/v1.2.1
https://github.com/mark3labs/mcp-go/security/advisories/GHSA-xf6j-693p-wqxx
https://www.vulncheck.com/advisories/mcp-go-before-1.2.1-origin-validation-error-via-unvalidated-well-known-protected-resource-metadata

Source data: NVD (nvd.nist.gov), public domain. Exploit-DB.ai adds local AI analysis for defensive use only.

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