CVE-2026-108586

1MCP Agent (@1mcp/agent) 0.20.0 through 0.39.0 contains an incorrect authorization vulnerability that allows authenticated clients to bypass OAuth tag-scope enforcement using negated advanced tag-filter expressions. Attackers holding a single-tag token can send a filter like not <granted-tag> to list and invoke tools on backend MCP servers outside their granted scopes.

• github.comhttps://github.com/1mcp-app/agent
• github.comhttps://github.com/1mcp-app/agent/blob/v0.39.0/src/sdk/legacy/transport/http/middlewares/scopeAuthMiddleware.ts#L163-L183
• github.comhttps://github.com/1mcp-app/agent/blob/v0.39.0/src/transport/http/routes/inspectHelpers.ts#L79-L102
• hackmd.iohttps://hackmd.io/@haind/1mcp-negated-tag-filter-oauth-scope-bypass
• www.vulncheck.comhttps://www.vulncheck.com/advisories/1mcp-agent-0.20.0-through-0.39.0-oauth-tag-scope-bypass-via-negated-tag-filter