CVE-2026-79537

Deferred Deferred - Pending Action

IDOR Vulnerability in MetaMCP Exposes Tenant Data

Publication date: 2026-09-29

Last updated on: 2026-09-30

Assigner: MITRE

Description

metatool-ai MetaMCP through 2.4.22 contains an insecure direct object reference (IDOR) in the MCP transport session dispatch. The session store (getSession in session-lifetime-manager.ts) is keyed only by the client-supplied mcp-session-id header with no owner, namespace, or endpoint binding, and the per-endpoint authorization middleware validates only the URL endpoint's owner, never the session. An attacker who supplies another tenant's session id " obtained without authentication from GET /metamcp/health/sessions, which discloses active session IDs and namespace UUIDs " can list and execute the victim tenant's private MCP tools and exfiltrate their data using the victim's forwarded credentials.

CVSS Scores

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Meta Information

Published

2026-09-29

Last Modified

2026-09-30

Generated

2026-10-19

AI Q&A

2026-09-29

EPSS Evaluated

2026-10-18

NVD

CVE-2026-79537

EUVD

EUVD-2026-89362

Affected Vendors & Products

Vendor	Product	Version / Range
metatool-ai	metamcp	to 2.4.22 (inc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-639	The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data.

Attack-Flow Graph

Executive Summary

This vulnerability is an insecure direct object reference (IDOR) in MetaMCP through version 2.4.22. It allows an attacker to access another tenant's private MCP tools and data by using a session ID obtained without authentication from the /metamcp/health/sessions endpoint. The session store is only keyed by a client-supplied header with no owner or namespace binding, and authorization checks only validate the URL endpoint's owner, not the session itself.

Detection Guidance

To detect this vulnerability, inspect network traffic for unauthorized access to MCP endpoints using session IDs obtained from /metamcp/health/sessions without authentication. Check logs for requests with mcp-session-id headers that bypass endpoint authorization checks.

Impact Analysis

An attacker could exploit this to list and execute private tools of another tenant, access their sensitive data, and exfiltrate information using the victim's credentials. This could lead to data breaches, unauthorized actions, or loss of confidential information depending on the MCP tools and data involved.

Compliance Impact

The vulnerability allows unauthorized access to another tenant's session data, enabling exfiltration of private MCP tools and sensitive information using stolen session IDs. This could violate data protection requirements under GDPR (e.g., unauthorized access to personal data) and HIPAA (e.g., exposure of protected health information) due to insufficient session isolation and lack of proper access controls.

Mitigation Strategies

Update metatool-ai MetaMCP to a version beyond 2.4.22 where the session store is properly secured with owner, namespace, or endpoint binding to prevent unauthorized access.

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