Improper Authentication in SurrealDB Leading to Session Hijacking

Executive Summary

CVE-2026-121419 is an improper authentication vulnerability in SurrealDB versions 3.1.0 to 3.2.x. It allows session hijacking via a fingerprint collision in the MCP HTTP transport. The BoundSubject fingerprint uses the access method name instead of the user's unique identity for JWT/Bearer tokens. This lets any authenticated user of the same access method hijack another user's MCP session using their valid token and the victim's session ID, executing MCP tools with the victim's roles and permissions.

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Detection Guidance

To detect this vulnerability, check if your SurrealDB instance is running version 3.1.0 to 3.2.9 and if MCP is exposed over HTTP (POST /mcp). Inspect logs for session hijacking attempts or unusual privilege escalations. No specific commands are provided in the resources, but monitoring for unauthorized MCP tool execution or session ID reuse may indicate exploitation.

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Impact Analysis

An attacker with a low-privilege token for the same access method and the victim's mcp-session-id can hijack the victim's session. This allows privilege escalation, where the attacker executes MCP tools with the victim's roles and permissions. For example, a user with viewer privileges could perform actions restricted to an editor role. The activity is logged under the victim's identity, making it difficult to detect.

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Compliance Impact

This vulnerability could lead to unauthorized access to sensitive data, violating confidentiality requirements in GDPR and HIPAA. Session hijacking and privilege escalation may result in data breaches, non-compliance with access control policies, and failure to meet audit logging standards. Organizations using affected SurrealDB versions must address this flaw to maintain compliance.

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Mitigation Strategies

Upgrade SurrealDB to version 3.3.0 or later immediately. If upgrading is not possible, disable MCP over HTTP (POST /mcp) or restrict access to trusted users only. Ensure JWT/Bearer tokens use per-user identity (e.g., the 'sub' claim) for actor ID construction. Review and revoke any potentially compromised sessions.

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