CVE-2026-106119: LangChain: MongoDBChatMessageHistory query injection can allow cross-session access

MongoDBChatMessageHistory did not enforce the documented string type for session identifiers at runtime. In affected applications, a structured session identifier could be interpreted as a MongoDB query condition rather than as a literal identifier.

Applications are affected when they pass untrusted session identifier input to MongoDBChatMessageHistory and store multiple users’ histories in the same collection. An attacker who can invoke chat-history operations may be able to read, modify, or delete another user’s stored conversation.

Applications that derive the session identifier from an authenticated, server-controlled value and enforce its type are not affected by this path.