Adam Štorek Columbia University, Mukur Gupta, Samira Hajizadeh, Prashast Srivastava Amazon, Suman Jana , Columbia University
Large language models (LLMs) are increasingly deployed for understanding large codebases, but whether they understand operational semantics of long code context or rely on pattern matching shortcuts remains unclear. We distinguish between lexical recall (retrieving code verbatim) and semantic recall (understanding operational semantics). Evaluating 10 state-of-the-art LLMs, we find that while frontier models achieve near-perfect, position-independent lexical recall, semantic recall degrades severely when code is centrally positioned in long contexts. We introduce semantic recall sensitivity to measure whether tasks require understanding of code’s operational semantics vs. permit pattern matching shortcuts. Through a novel counterfactual measurement method, we show that models rely heavily on pattern matching shortcuts to solve existing code understanding benchmarks. We propose a new task SemTrace, which achieves high semantic recall sensitivity through unpredictable operations; LLMs’ accuracy exhibits severe positional effects, with median accuracy drops of 92.73% versus CRUXEval’s 53.36% as the relevant code snippet approaches the middle of the input code context. Our findings suggest current evaluations substantially underestimate semantic recall failures in long context code understanding.
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cs.CL
Proceedings of the 64th Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers) · 2026 · 正式发表
Adam Štorek Columbia University, Mukur Gupta, Noopur Bhatt University of Pennsylvania, University of Pennsylvania and Leidos Inc., Aditya Gupta, Janie Kim Google, Prashast Srivastava Amazon, Suman Jana , Columbia University
AI coding assistants automatically gather context from potentially untrusted sources to generate code recommendations. We introduce Cross-Origin Context Poisoning (XOXO), a novel attack that exploits this automatic context inclusion by subtly manipulating code without changing its semantics. Attackers introduce semantics-preserving transformations (e.g., renamed variables) to shared code, causing AI assistants to unknowingly recommend vulnerable code patterns to victims. To systematically identify effective transformations, we present Greedy Cayley Graph Search (GCGS), a black-box algorithm that efficiently composes transformations to identify adversarial inputs. Our evaluation demonstrates XOXO’s effectiveness at making LLMs generate buggy and vulnerable code, achieving average attack success rates of 73.20% against eight state-of-the-art models including GPT 4.1 and Claude 3.5 Sonnet v2, with vulnerability injection rates up to 66.67%. We also demonstrate a real-world attack against GitHub Copilot, highlighting critical security gaps in current AI coding tools.
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cs.CL
Proceedings of the 64th Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers) · 2026 · 正式发表