CVE-2026-40087 | langchain-ai langchain up to 0.3.82/1.2.27 special elements used in a template engine

VDB-356681 · CVE-2026-40087 · GCVE-0-2026-40087 LANGCHAIN-AI LANGCHAIN UP TO 0.3.82/1.2.27 SPECIAL ELEMENTS USED IN A TEMPLATE ENGINE HISTORYDIFFRELATEJSONXMLCTI CVSS Meta Temp Score Current Exploit Price (≈) CTI Interest Score 5.2 $0-$5k 1.37 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. 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 🔒 🔒 🔒 CPE 2.2info 🔒 🔒 🔒 CVSSv4info VulDB Vector: 🔒 VulDB Reliability: 🔍 CVSSv3info VulDB Meta Base Score: 5.3 VulDB Meta Temp Score: 5.2 VulDB Base Score: 5.3 VulDB Temp Score: 5.1 VulDB Vector: 🔒 VulDB Reliability: 🔍 CNA Base Score: 5.3 CNA Vector (GitHub_M): 🔒 CVSSv2info Vector Complexity Authentication Confidentiality Integrity Availability Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock VulDB Base Score: 🔒 VulDB Temp Score: 🔒 VulDB Reliability: 🔍 Exploitinginfo Class: Improper neutralization of special elements used in a template engine CWE: CWE-1336 / CWE-791 / CWE-790 CAPEC: 🔒 ATT&CK: 🔒 Physical: No Local: No Remote: Yes Availability: 🔒 Status: Not defined Price Prediction: 🔍 Current Price Estimation: 🔒 0-Day Unlock Unlock Unlock Unlock Today Unlock Unlock Unlock Unlock Threat Intelligenceinfo Interest: 🔍 Active Actors: 🔍 Active APT Groups: 🔍 Countermeasuresinfo Recommended: Upgrade Status: 🔍 0-Day Time: 🔒 Upgrade: langchain 0.3.83/1.2.28 Timelineinfo 04/09/2026 Advisory disclosed 04/09/2026 +0 days CVE reserved 04/09/2026 +0 days VulDB entry created 04/09/2026 +0 days VulDB entry last update Sourcesinfo Product: github.com Advisory: github.com Status: Confirmed CVE: CVE-2026-40087 (🔒) GCVE (CVE): GCVE-0-2026-40087 GCVE (VulDB): GCVE-100-356681 Entryinfo Created: 04/09/2026 22:13 Changes: 04/09/2026 22:13 (63) Complete: 🔍 Cache ID: 99:A35:101 Discussion No comments yet. 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