Grounded or Gamed? We Audited Our Own Cyber Benchmark

Semgrep audited its own LLM benchmark for IDOR vulnerability detection after a viral model score raised doubts about whether models truly reason or just pattern match. It built four groundedness metrics—counterfactual (patch the bug, the finding should vanish), metamorphic (rename identifiers, the finding should persist), selectivity (don't flag safe look-alikes), and stability across repeated scans—and tested Kimi K2.7, GLM-5.2, MiniMax M3, Opus 4.8, GPT-5.5, and its own Semgrep Multimodal on its hardest repo. Verdict: nobody is gaming the benchmark—counterfactual and selectivity scores are near 1, so findings are causal rather than surface matches. The real problem is recall: of 27 real IDORs, 19 (70%) were missed by every model, and pooling all five models bought only one extra vulnerability. Misses split into depth (authorization logic spread across the request path) and familiarity (models catch the textbook file-download IDOR but miss the identical bug on other endpoints). A preview shows GLM stays grounded on SSRF but coverage collapses from 22% to 5.6%. The post is candid about limits—one repo, varying harnesses, no precision re-scoring—and concludes grounding is table stakes while recall is the frontier. 

https://semgrep.dev/blog/2026/grounded-or-gamed-we-audited-our-own-cyber-benchmark/

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