arXiv subjects

Ashish Kundu

Publications and source records attributed to Ashish Kundu.

3 recordsLinked to original sources

arXiv2026

Characterizing Privacy-Audit Alignment in Behavioral Audit of Machine Unlearning

The removal of learned data from Machine Learning models through Machine Unlearning (MU) has been widely studied; however, there is no agreed-upon scheme for auditing MU. Existing work shows that a dishonest model owner can falsify evidence to avoid executing MU, while curious auditors (and adversaries) can infer privacy-sensitive properties of the model and its training data even with limited access. Yet auditing of MU under mutual distrust between the model owner and the auditor remains unexplored. In this paper, we characterize how much a generic audit scheme that relies solely on querying the model for behavioral signals inevitably results in privacy leakage related to the retained set by providing a geometric transfer theorem that establishes a lower bound on retained set membership distinguishability based on the audit accuracy. In addition, we study how the unlearned set, target sample, and query protocol jointly determine the privacy-audit transfer coefficient through local and global model-parameter-space geometry. Our empirical experiments on both convex and non-convex models strongly support these results. Our results call for more careful consideration of the privacy-audit tension under a realistic auditor model and serve as a foundation for greater scrutiny of privacy-preserving audit scheme designs for the MU pipeline.

cs.LG↗

arXiv2026

Refusing the Impossible: A Taxonomy and Benchmark for Code Hallucination in Large Language Models

Large language models (LLMs) often produce code that looks plausible but is not grounded in reality. The code may import packages that do not exist or claim to implement algorithms that violate proven theorems, while still compiling and running. We study \emph{code hallucination} as \emph{ungrounded generation} and separate it from ordinary \emph{code error} (bugs in otherwise grounded programs). We propose a taxonomy with three dimensions: \textbf{groundedness} (absolute violations of universal truths vs.\ relative fabrications of contingent or ecosystem-specific facts), \textbf{manifestation level} (syntactic, semantic, or factual), and \textbf{behavior} (from confident fabrication to degenerate output), organized into a severity ordering. We build an \textbf{adversarial} suite of deliberately unsatisfiable tasks where the correct response is to refuse and categorize the responses under our taxonomy. The suite contains \textbf{270 prompts} across six languages and 24 subcategories, paired with \textbf{91 matched solvable controls}, and responses are judged by a two-tier protocol validated against human labels (82\% agreement, $κ{=}0.73$). Across twelve open-weight code and reasoning models (4{,}332 judged responses), models produce ungrounded code on about 60\% of unsatisfiable prompts and refuse only 27\%, while wrongly refusing 0\% of the solvable controls.

cs.SE↗

arXiv2026

PhantomCall: Evading ML Malware Detectors via Function Call Graph Perturbation

Prior adversarial attacks on Windows PE malware detectors target raw bytes, PE headers, or intra-function control-flow graphs, leaving the function call graph (FCG) unexplored as an attack surface. Yet the FCG structure is an important feature in graph-based malware detectors. We present Phan- tomCall, a black-box attack that perturbs the FCG of Windows PE malware by injecting fully executable dummy functions at targeted call sites, adding new nodes and edges to both the CFG and FCG while preserving program semantics. We pair this structural perturbation with classifier-guided search and tunable injection parameters, effective across three archi- tecturally distinct classifiers. Evaluated on a 2025-collected Windows malware corpus against MalConv (raw-byte CNN), MalGraph (graph-based GNN), and SAFE+GNN (pure FCG GNN trained from scratch on a 2024 corpus) at two FPR thresholds, the best PhantomCall variant achieves 85-100% attack success rate across all configurations, exceeding prior state-of-the-art by up to 14.78 percentage points on MalGraph and 95.5 percentage points on SAFE+GNN, and generating evasive variants up to 2.9x faster on average across all targets. For MalConv and MalGraph, the majority of evasions require only a single call site modification, and 86-97% of evaluated evasive variants preserve the original malicious behavior in sandbox-based semantic testing across all configurations.

cs.CR↗