CVE-2026-40087

CVSS Score & Metrics

Base Score

5.3 / 10

Vector String

                                        CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N                                    

Vulnerability Description

LangChain is a framework for building agents and LLM-powered applications. Prior to 0.3.84 and 1.2.28, LangChain's f-string prompt-template validation was incomplete in two respects. First, some prompt template classes accepted f-string templates and formatted them without enforcing the same attribute-access validation as PromptTemplate. In particular, DictPromptTemplate and ImagePromptTemplate could accept templates containing attribute access or indexing expressions and subsequently evaluate those expressions during formatting. Second, f-string validation based on parsed top-level field names did not reject nested replacement fields inside format specifiers. In this pattern, the nested replacement field appears in the format specifier rather than in the top-level field name. As a result, earlier validation based on parsed field names did not reject the template even though Python formatting would still attempt to resolve the nested expression at runtime. This vulnerability is fixed in 0.3.84 and 1.2.28.

Vulnerability Details

Published Date

April 08, 2026

Last Modified

April 13, 2026

CWE ID

CWE-1336

Source

GitHub

Vendor

pip

Product

langchain-core

CVSS Score & Metrics

Vulnerability Description

Vulnerability Details

External References

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