LangChain: MongoDBChatMessageHistory query injection can allow cross-session access

## 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.

Source published

8 Oct 2026 17:52:22 UTC

Source modified

8 Oct 2026 18:00:08 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N

Publisher rating · MODERATE