LangChain is a framework for building LLM-powered applications. Prior to 1.3.1, MongoDBChatMessageHistory does not enforce the documented string type for an untrusted structured session identifier at runtime, allowing the identifier to be interpreted as a MongoDB query condition rather than as a literal value when multiple users' histories are stored in a shared MongoDB collection. An attacker able to invoke chat-history operations can read, modify, or delete another user's stored conversation. Applications using authenticated, server-controlled string identifiers are not affected. This issue is fixed in version 1.3.1.

Affected: npm: @langchain/mongodb

## Impact

`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.

## Patches

The issue is fixed in `@langchain/mongodb` version **1.3.1**.

Users of affected versions should upgrade to version 1.3.1 or later. The patched version validates session identifiers at runtime and ensures they are compared as literal values in MongoDB queries.

## Workarounds

If an immediate upgrade is not possible, applications must reject session identifiers that are not non-empty strings. Session identifiers should be derived from an authenticated, server-controlled value and must not be passed directly from an untrusted request field.

Upgrading remains the recommended remediation.