CVE-2026-40087

[CVE catalog]

Severity

Medium · CVSS 5.3CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Published

Apr 8, 2026, 10:00:00 PM UTC

Source

[NVD] · [CVE record]

EPSS

0.26% · Oct 25, 2026

A flaw was found in LangChain. A missing validation of f-string prompt templates in some classes, specifically in `DictPromptTemplate` and `ImagePromptTemplate`, can cause the evaluation of attribute access or indexing expressions during template formatting. Also, f-string validation based on parsed top-level field names did not reject nested replacement fields inside format specifiers. A remote attacker can exploit this issue by providing a specially crafted prompt template, potentially leading to information disclosure. langchain: incomplete f-string validation in prompt templates To exploit this vulnerability, an attacker needs to supply a specially crafted input to the `DictPromptTemplate` or `ImagePromptTemplate` classes. The payload must contain Python attribute access expressions (e.g., accessing internal object classes), which bypass the template validator and get executed by the underlying f-string formatter, potentially causing information disclosure. There is no memory corruption or arbitrary code execution. Due to these reasons, this flaw has been rated with a moderate severity. The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.