CVE-2026-40087
This vulnerability is fixed in 0.3.84 and 1.2.28.
Does this matter?
Lower severity and a low EPSS score (0.26%). Track it; it rarely justifies an emergency change on its own.
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.
- CVSS 3.1
- 5.3 MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
- EPSS
- 0.26% probability · 18th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-1336
- Affected
- langchain/langchain core
- Source
- security-advisories@github.com
References
- https://github.com/langchain-ai/langchain/commit/6bab0ba3c12328008ddca3e0d54ff5a6151cd27bPatch
- https://github.com/langchain-ai/langchain/commit/af2ed47c6f008cdd551f3c0d87db3774c8dfe258Patch
- https://github.com/langchain-ai/langchain/pull/36612Issue Tracking, Patch
- https://github.com/langchain-ai/langchain/pull/36613Issue Tracking, Patch
- https://github.com/langchain-ai/langchain/releases/tag/langchain-core%3D%3D0.3.84Product, Release Notes
- https://github.com/langchain-ai/langchain/releases/tag/langchain-core%3D%3D1.2.28Product, Release Notes
- https://github.com/langchain-ai/langchain/security/advisories/GHSA-926x-3r5x-gfhwMitigation, Vendor Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.