CVE-2026-108586
MEDIUM 5.31MCP 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.
No known exploitation, public exploit, or elevated probability at this time. Track for changes.
Exploitation likelihood
0.2%chance of exploitation in 30 days · 9th percentile
Impact if exploited
5.3CVSS 4.0 · MEDIUM
- ConfidentialityLow
- IntegrityLow
- AvailabilityNone
What an attacker needs
- ✓Access: Reachable over the network — no local access needed
- ⚠Privileges: Requires a low-privilege account
- ✓User interaction: No user interaction needed
- ✓Complexity: No special conditions — reliably repeatable
- ✓Requirements: No special attack requirements
✓ lowers the bar for an attacker · ⚠ raises it
Proof of concept
No public PoC is currently catalogued.
Search for new PoCs
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Tracked sources are checked daily for recent CVEs, including PoCs published after the original disclosure. A later release appears after a tracked source lists it and a refresh succeeds.
Data snapshot:
Weakness (CWE)
- CWE-863: Incorrect Authorization
CVSS vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N
References and research data (JSON)
All CVSS metrics
- MEDIUM 5.3 v4.0 · CNA Primary
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N - MEDIUM 5.4 v3.1 · CNA Primary
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N - MEDIUM 5.3 v4.0 · NVD Secondary
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X - MEDIUM 5.4 v3.1 · NVD Secondary
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
References
Advisories
- https://hackmd.io/@haind/1mcp-negated-tag-filter-oauth-scope-bypass CVE record · VulnCheck · Updated 2026-10-10T16:14:10.297Z
NVD · CVE-2026-108586 · Updated 2026-10-16T19:21:14.417 - https://www.vulncheck.com/advisories/1mcp-agent-0.20.0-through-0.39.0-oauth-tag-scope-bypass-via-negated-tag-filter CVE record · VulnCheck · Updated 2026-10-10T16:14:10.297Z
NVD · CVE-2026-108586 · Updated 2026-10-16T19:21:14.417 - https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-96373 EUVD · EUVD-2026-96373
Technical & other
- https://github.com/1mcp-app/agent/blob/v0.39.0/src/sdk/legacy/transport/http/middlewares/scopeAuthMiddleware.ts#L163-L183 CVE record · VulnCheck · Updated 2026-10-10T16:14:10.297Z
NVD · CVE-2026-108586 · Updated 2026-10-16T19:21:14.417 - https://github.com/1mcp-app/agent/blob/v0.39.0/src/transport/http/routes/inspectHelpers.ts#L79-L102 CVE record · VulnCheck · Updated 2026-10-10T16:14:10.297Z
NVD · CVE-2026-108586 · Updated 2026-10-16T19:21:14.417 - https://github.com/1mcp-app/agent CVE record · VulnCheck · Updated 2026-10-10T16:14:10.297Z
NVD · CVE-2026-108586 · Updated 2026-10-16T19:21:14.417