Auth bypass in 1mcp-App @1mcp/agent
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.
Vulnerability class: Broken Access Control
Published .
CVSS v3 metric
CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N.
EPSS exploit prediction
No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.
Affected products
Weakness classification (CWE)
References
- hackmd.io/@haind/1mcp-negated-tag-filter-oauth-scope-bypass (third-party-advisory)
- github.com/1mcp-app/agent/blob/v0.39.0/src/sdk/legacy/transport/http/middleware… (technical-description)
- github.com/1mcp-app/agent/blob/v0.39.0/src/transport/http/routes/inspectHelpers… (technical-description)
- github.com/1mcp-app/agent (product)
- www.vulncheck.com/advisories/1mcp-agent-0.20.0-through-0.39.0-oauth-tag-scope-b… (third-party-advisory)
Frequently asked questions
- What is CVE-2026-108586?
- CVE-2026-108586 is a medium-severity vulnerability in 1mcp-App @1mcp/agent, classified under Incorrect Authorization. CVSS score: 5.4/10. Published 2026-10-10.
- How severe is CVE-2026-108586?
- Medium severity. CVSS v3 base score is 5.4 out of 10.