Microsoft Semantic Kernel In-Memory Vector Store eval() RCE (CVE-2026-26030) - ATR-2026-00440 (567d04f8-ec82-5a9c-b673-6cb02f891815)
Detects exploitation of CVE-2026-26030 (Critical), remote code execution in Microsoft Semantic Kernel via unsafe string interpolation in In-Memory Vector Store filter functions. The vulnerable sink interpolates a user/LLM-controlled filter expression and evaluates it as a lambda; attacker constructs a lambda body that traverses Python's class hierarchy via tuple() to reach BuiltinImporter and execute os.system(), achieving unauthenticated RCE on the Semantic Kernel host. This rule detects the LLM-output / user-input payload patterns that reach the filter sink: lambda definitions combined with eval / import / AST-traversal-via-mro patterns inside content or user_input fields a Semantic Kernel agent is likely to interpolate. CWE-94, CWE-95. Patches available in Python semantic-kernel >= 1.39.4 and .NET semantic-kernel >= 1.71.0; this rule detects exploit attempts against unpatched deployments and provides defence-in-depth post-patch.