Code Monitor Red Teaming for Public-Test-Passing Code

Junchi Liao, Jiawen Deng, Fuji Ren


Abstract
Visible tests are a common gate for LLM-generated code, but passing them does not certify specification correctness. We study a deployment-like monitoring problem: after code has passed public tests, can a weaker LLM verifier identify the residual hidden bugs? We introduce Code Monitor Red Teaming, a monitor-red-teaming protocol that fixes a public-check information boundary while varying generator pressure, verifier scaffolding, and weak-to-strong capability. We instantiate it as CodeMonitorBench, spanning function-level, data-science, and workflow code. Across 71,000 generated candidates, 43,677 pass public tests and 23,081 of those fail hidden tests. Weak verifiers improve with scaffolding and model family, but still miss most hidden bugs at 5% false-positive rate. As a robustness stress test, adversarial public-test-overfit pressure lowers verifier AUROC and raises low-FPR miss rates in most cells. A GLM-5.1 verifier recovers part of the gap under the same evidence boundary; an inferability audit shows that remaining misses mix verifier failures with M1 evidence limits.
Anthology ID:
2026.findings-emnlp.177
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
3720–3740
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.177/
DOI:
Bibkey:
Cite (ACL):
Junchi Liao, Jiawen Deng, and Fuji Ren. 2026. Code Monitor Red Teaming for Public-Test-Passing Code. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 3720–3740, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Code Monitor Red Teaming for Public-Test-Passing Code (Liao et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-emnlp.177.pdf