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Model Unmerging: Making Your Models Unmergeable for Secure Model Sharing

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arxiv 2509.01548 v1 pith:3GYVRSAK submitted 2025-09-01 cs.LG

Model Unmerging: Making Your Models Unmergeable for Secure Model Sharing

classification cs.LG
keywords modelmodelsmergingfinetunedmergedmergelockunauthorizedattention
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved
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Model merging leverages multiple finetuned expert models to construct a multi-task model with low cost, and is gaining increasing attention. However, as a growing number of finetuned models become publicly available, concerns about the safety of model merging have emerged. Unauthorized merging may infringe on developers' rights and risk leaking sensitive personal information. Most existing methods focus on detecting whether a merged model originates from a specific source model, but fail to effectively prevent illegal merging. In this paper, we propose MergeLock, an active protection mechanism that disrupts model parameters to render them unmergeable, thereby directly preventing unauthorized model merging. Specifically, leveraging the inherent symmetry of the attention mechanism in Transformer-based models, we randomly sample two pairs of invertible matrices and apply them to the Query-Key (QK) and Value-Output (VO) branches. This transformation keeps the model's output unchanged while pushing it away from the shared parameter space of other finetuned models. Extensive experiments across both vision and language tasks demonstrate that MergeLock can degrade the performance of merged models by over 95% when a protected model is involved in most cases, demonstrating its effectiveness. Moreover, we further demonstrate that merged models protected by MergeLock cannot be effectively recovered using low-cost restoration methods, further enhancing robustness against unauthorized merging. The code is available at https://github.com/hetailang/Merge-Lock.

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Forward citations

Cited by 6 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. Efficient Decentralized Multi-task Dataset Valuation via Model Merging

    cs.CL 2026-07 conditional novelty 7.0

    Task-arithmetic model merging approximates multi-task coalition utilities well enough to recover Dataset Shapley rankings privately and without retraining.

  2. Locking Pretrained Weights via Deep Low-Rank Residual Distillation

    cs.LG 2026-05 unverdicted novelty 7.0

    DLR-Lock locks open-weight LLMs against unauthorized fine-tuning by swapping MLPs for deep low-rank residual networks that inflate backprop memory and complicate optimization, yet preserve original capabilities via mo...

  3. Generalizing the Geometry of Model Merging Through Frechet Averages

    cs.LG 2026-04 unverdicted novelty 7.0

    Model merging is reframed as Fréchet averaging on manifolds whose geometry respects architectural symmetries, generalizing Fisher merging and enabling better LoRA merges.

  4. Generalizing the Geometry of Model Merging Through Frechet Averages

    cs.LG 2026-04 unverdicted novelty 7.0

    Model merging is generalized as Fréchet averaging on symmetry-invariant manifolds, containing Fisher merging as a special case and offering a new approach for LoRA adapters.

  5. Making Models Unmergeable via Scaling-Sensitive Loss Landscape

    cs.AI 2026-01 conditional novelty 7.0

    TRAP² fine-tunes model updates so that standalone accuracy stays high while any re-scaling during merging reliably collapses task accuracy, across transformer and ConvNeXt backbones.

  6. On the Vulnerability of Parameter-Level Defenses to Model Merging

    cs.LG 2026-06 unverdicted novelty 5.0

    Parameter-level defenses for model merging are vulnerable to Anchor-Guided Attack because protected weights are dominated by the pretrained model, and a new defense ARF is introduced to counter it.