Open-source Large Language Models (LLMs) often employ safety alignment methods to resist harmful instructions. However, recent research shows that maliciously fine-tuning these LLMs on harmful data can easily bypass these safeguards. To counter this, we theoretically uncover why malicious fine-tuning succeeds and identify potential defense strategies. Building on the theoretical analysis, we introduce the Self-Degraded Defense (SDD) framework. SDD encourages LLMs to produce high-quality but irrelevant responses to harmful prompts. When attackers attempt malicious fine-tuning, the general capability of the LLM aligned by SDD will significantly decrease, rendering it incapable of following harmful instructions. Our experimental results confirm SDD's effectiveness against such attacks.
@article{arxiv.2507.21182,
title = {SDD: Self-Degraded Defense against Malicious Fine-tuning},
author = {Zixuan Chen and Weikai Lu and Xin Lin and Ziqian Zeng},
journal= {arXiv preprint arXiv:2507.21182},
year = {2025}
}