CUSE: Fine-Grained Multimodal Unlearning with Counterfactual Guidance and On-Policy Self-Distillation

Multimodal large language models (MLLMs) may memorize sensitive cross-modal information during pretraining, making machine unlearning (MU) crucial. Existing methods typically evaluate unlearning effectiveness based on output deviations, while overlooking the generation quality after unlearning. This can easily lead to hallucinated or rigid responses, thereby affecting the usability and safety of the unlearned model. To address this issue, we propose ASRU, a controllable multimodal unlearning framework that incorporates generation quality as a core evaluation objective. ASRU first induces initial refusal behavior through activation redirection, and then optimizes fine-grained refusal boundaries using a customized reward function, thereby achieving a better trade-off between target knowledge unlearning and model utility. Experiments on Qwen3-VL show that ASRU significantly improves unlearning effectiveness (+24.6%) on average and generation quality (5.8X) on average while effectively preserving model utility, using only a small amount of retained supervision data.

Multimodal large language models (MLLMs) can memorize and disclose sensitive information, motivating machine unlearning to remove designated knowledge while preserving model utility. Existing privacy-oriented benchmarks mainly study profile-level deletion, whereas practical requests often require finer-grained forgetting: removing a sensitive attribute while retaining other information about the same identity. We introduce attribute-level MLLM unlearning and construct AMU-Bench, covering long-text, numeric, and short-text targets, multiple forget ratios, and diverse question types. Our evaluation shows that target and retain attributes share identity-specific and visual evidence, making selective forgetting prone to residual leakage and collateral degradation. To address this challenge, we propose Causal Localization and Retain-Aware Projection (CLRP), a lightweight, training-free framework that localizes causally relevant layers and projects intermediate representations away from target-specific subspaces while preserving retain-related information. Experiments across MLLMs with different architectures and scales show that CLRP achieves a strong forgetting--retention trade-off on AMU-Bench. For example, at a 5% forget ratio, CLRP reduces Attribute Forget Set cloze accuracy from 20.00% to 4.00% while improving Attribute Retain Set accuracy from 14.77% to 17.79% in the reported LLaVA-1.5-7B and Qwen2.5-VL-3B results. These findings demonstrate effective and selective attribute-level unlearning without modifying model parameters.

Multimodal Large Language Models (MLLMs) have achieved remarkable progress on vision-language tasks, but they may also memorize and expose sensitive or restricted knowledge, raising concerns about privacy and broader safety risks. Machine Unlearning (MU) provides a promising way to remove targeted undesirable knowledge from trained models without retraining from scratch while preserving general model utility. Nevertheless, effective unlearning in MLLMs remains particularly challenging. Existing training-based methods often struggle to balance unlearning effectiveness and model utility. In contrast, training-free methods such as in-context unlearning preserve model utility by avoiding parameter updates, but they do not remove memorized knowledge at the parameter level and may remain vulnerable to reverse-engineering attacks. More importantly, in-context unlearning is insufficient in multimodal settings, where visual inputs can provide strong conditioning signals and induce undesirable outputs. To address these challenges, we propose Visual-Noise Guided In-Context Distillation (VGID), a distillation-based framework for MLLM unlearning. VGID dynamically constructs an unlearning-oriented teacher distribution from the frozen base model through dual-modal intervention that combines visual perturbation with textual in-context unlearning. The resulting intervention-induced distribution serves as a teacher signal for distillation, guiding the student model toward parameter-level unlearning without requiring external teacher models or explicit undesirable response annotations. Experimental results show that VGID achieves strong unlearning effectiveness while preserving competitive model utility, reducing forget set ROUGE-L by 0.371 with only a 0.055 drop in retain set ROUGE-L in a representative setting.