From Evaluation to Optimisation: Hierarchy-Aware Training Signals for CWE Prediction in Python

Abstract:The original ALPHA benchmark introduced a taxonomy-aware penalty for evaluating CWE-level vulnerability prediction in Python and proposed that the penalty could theoretically also serve as a training signal. This paper provides that validation. We compare three delivery mechanisms: supervised fine-tuning, a dual-head classification loss, and reinforcement learning with a dense reward derived from the normalised penalty. We find that supervised approaches consistently regress below the zero-shot baseline under distribution shift, while GRPO succeeds. Our best policy reduces the cumulative ALPHA penalty of Qwen2.5-Coder-7B on Security Hardening and Adversarial Testing (SVEN) dataset by 27.9% under greedy decoding, and by 25.5% under sampled decoding(p = 0.005, Welch's t-test), reaching statistical parity with its 4.5x larger zero-shot teacher. We conclude that the value of a hierarchical penalty as a training signal depends largely on the directness of its delivery.

Machine Learning (cs.LG)

arXiv:2607.21069 [cs.LG]

(or arXiv:2607.21069v1 [cs.LG] for this version)

https://doi.org/10.48550/arXiv.2607.21069 Focus to learn more arXiv-issued DOI via DataCite (pending registration)

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