langchain-ai langchain up to 0.3.82/1.2.27 special elements used in a template engine

Summaryinfo

A vulnerability has been found in langchain-ai langchain up to 0.3.82/1.2.27 and classified as problematic. The affected element is an unknown function. The manipulation leads to improper neutralization of special elements used in a template engine. This vulnerability is documented as CVE-2026-40087. The attack can be initiated remotely. There is not any exploit available. The affected component should be upgraded.

Detailsinfo

A vulnerability, which was classified as problematic, has been found in langchain-ai langchain up to 0.3.82/1.2.27. This issue affects an unknown part. The manipulation with an unknown input leads to a improper neutralization of special elements used in a template engine vulnerability. Using CWE to declare the problem leads to CWE-1336. The product uses a template engine to insert or process externally-influenced input, but it does not neutralize or incorrectly neutralizes special elements or syntax that can be interpreted as template expressions or other code directives when processed by the engine. Impacted is confidentiality. The summary by CVE is:

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.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-40087 since 04/09/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Neither technical details nor an exploit are publicly available. MITRE ATT&CK project uses the attack technique T1221 for this issue.

Upgrading to version 0.3.83 or 1.2.28 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at CERT Bund (WID-SEC-2026-1434). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Affected

• IBM App Connect Enterprise

Productinfo

Type

• Artificial Intelligence Software

Vendor

• langchain-ai

Name

• langchain

Version

• 0.3.0
• 0.3.1
• 0.3.2
• 0.3.3
• 0.3.4
• 0.3.5
• 0.3.6
• 0.3.7
• 0.3.8
• 0.3.9
• 0.3.10
• 0.3.11
• 0.3.12
• 0.3.13
• 0.3.14
• 0.3.15
• 0.3.16
• 0.3.17
• 0.3.18
• 0.3.19
• 0.3.20
• 0.3.21
• 0.3.22
• 0.3.23
• 0.3.24
• 0.3.25
• 0.3.26
• 0.3.27
• 0.3.28
• 0.3.29
• 0.3.30
• 0.3.31
• 0.3.32
• 0.3.33
• 0.3.34
• 0.3.35
• 0.3.36
• 0.3.37
• 0.3.38
• 0.3.39
• 0.3.40
• 0.3.41
• 0.3.42
• 0.3.43
• 0.3.44
• 0.3.45
• 0.3.46
• 0.3.47
• 0.3.48
• 0.3.49
• 0.3.50
• 0.3.51
• 0.3.52
• 0.3.53
• 0.3.54
• 0.3.55
• 0.3.56
• 0.3.57
• 0.3.58
• 0.3.59
• 0.3.60
• 0.3.61
• 0.3.62
• 0.3.63
• 0.3.64
• 0.3.65
• 0.3.66
• 0.3.67
• 0.3.68
• 0.3.69
• 0.3.70
• 0.3.71
• 0.3.72
• 0.3.73
• 0.3.74
• 0.3.75
• 0.3.76
• 0.3.77
• 0.3.78
• 0.3.79
• 0.3.80
• 0.3.81
• 0.3.82
• 1.2.0
• 1.2.1
• 1.2.2
• 1.2.3
• 1.2.4
• 1.2.5
• 1.2.6
• 1.2.7
• 1.2.8
• 1.2.9
• 1.2.10
• 1.2.11
• 1.2.12
• 1.2.13
• 1.2.14
• 1.2.15
• 1.2.16
• 1.2.17
• 1.2.18
• 1.2.19
• 1.2.20
• 1.2.21
• 1.2.22
• 1.2.23
• 1.2.24
• 1.2.25
• 1.2.26
• 1.2.27

Website

• Product: https://github.com/langchain-ai/langchain/

CPE 2.3info

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CPE 2.2info

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Entryinfo

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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