FineNib: A Query Synthesizer For Static Analysis of Security Vulnerabilities

CodeQL is a powerful static analysis engine that represents programs’ abstract syntax trees as databases that can be queried to detect security vulnerabilities. While CodeQL supports expressive interprocedural dataflow queries, the coverage and precision of its existing security queries remain limited, and writing new queries is challenging even for experts. Automatically synthesizing CodeQL queries from known vulnerabilities (CVEs) can provide fine-grained vulnerability signatures, enabling both improved detection and systematic variant analysis. We present FineNib, an agentic framework for synthesizing CodeQL queries from known CVE descriptions. FineNib leverages the Model Context Protocol (MCP) for agentic tool use, integrates abstract syntax tree guidance, and incorporates CodeQL’s language infrastructure and documentation into the synthesis loop. A key challenge is that state-of-the-art large language models hallucinate deprecated CodeQL syntax due to limited training data and outdated knowledge. FineNib addresses this by combining contextual engineering, iterative query feedback, and structured tool interaction to reliably generate executable, up-to-date queries.