arXiv Machine Learning August 27, 2026 By Sae Furukawa, Alina Oprea

Reconstruction of Personally Identifiable Information from Proprietary Data in Supervised Fine-Tuned Models

Read the original on arXiv Machine Learning →

The paper examines how supervised fine-tuning (SFT) of large language models can leak personally identifiable information (PII) when the fine-tuning data contains user-provided sensitive details. It introduces COVA, a coverage-aware decoding algorithm that improves targeted PII reconstruction from SFT models, especially when an adversary has limited contextual knowledge about a target. Experiments on medical and legal Q&A datasets show that even small proprietary SFT datasets can lead to significant privacy leakage via PII reconstruction.

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