Inadequate Template Validation in LangChain Framework by LangChain AI
CVE-2026-40087
What is CVE-2026-40087?
LangChain, a framework for developing agents and LLM-powered applications, suffers from improper validation of f-string templates. Before versions 0.3.84 and 1.2.28, certain prompt template classes, notably DictPromptTemplate and ImagePromptTemplate, permitted the use of f-string templates without enforcing necessary attribute-access validation akin to that of the PromptTemplate. This oversight enabled the evaluation of attribute access and indexing expressions during formatting. Furthermore, pre-existing validations based solely on top-level field names failed to recognize and reject nested replacement fields found within format specifiers. Consequently, Python's formatting mechanism attempted to resolve these nested expressions at runtime, leading to potential security risks. This vulnerability has been addressed in the mentioned versions.
Affected Version(s)
langchain < 0.3.83 < 0.3.83
langchain >= 1.0.0a1, < 1.2.28 < 1.0.0a1, 1.2.28