The DeepSeek MCP Server (arikusi deepseek-mcp-server) contains an authorization bypass vulnerability (CWE-639) in versions >=1.4.2 and <1.7.0. The process-global SessionStore accepts session_id values supplied by callers without verifying that these session IDs are bound to the authenticated principal or transport session. An attacker can enumerate active session IDs via the deepseek_sessions interface and then reuse a victim's session_id in the deepseek_chat interface to retrieve and continue the victim's conversation context. This vulnerability allows unauthorized access to another user's session data. The issue is fixed in version 1.7.0.

An attacker can gain unauthorized access to active user sessions by enumerating and reusing session IDs, leading to disclosure of sensitive conversation context and partial integrity and availability impacts. The CVSS score of 8.6 reflects high confidentiality impact, low integrity impact, and low availability impact. This can result in exposure of private communications without requiring authentication or user interaction.

A patch is available in version 1.7.0 that properly binds session IDs to authenticated principals and transport sessions, preventing unauthorized reuse. Users should upgrade to version 1.7.0 or later to remediate this vulnerability. No other mitigation guidance is provided or necessary as the patch addresses the root cause.