LangChain is affected by a deserialization of untrusted data vulnerability (CWE-502) in versions prior to 0.3.85 and from 1.0.0a1 up to but not including 1.3.3. The issue arises because certain runtime code paths deserialize inputs using an overly broad allowlist, specifically calling load() with allowed_objects="all". While this does not permit arbitrary Python object deserialization, it allows any trusted LangChain-serializable object to be revived, which is broader than necessary. Consequently, attacker-supplied serialized constructor dictionaries may cause trusted runtime paths to instantiate classes with untrusted constructor arguments. This vulnerability is addressed by updates in versions 0.3.85 and 1.3.3.

Successful exploitation could allow an attacker to supply crafted serialized data that causes the application to instantiate objects with untrusted constructor arguments. This may lead to unauthorized information disclosure (high confidentiality impact) and limited integrity impact. There is no reported impact on availability. No known exploits are currently reported in the wild.

Upgrading LangChain to version 0.3.85 or later, or 1.3.3 or later, fully addresses this vulnerability. No other official remediation or temporary fixes are documented. Users should apply these updates to ensure the vulnerability is mitigated.