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Image Hijacks: Adversarial Images can Control Generative Models at Runtime
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Introduces image hijacks, adversarial images that control VLM behaviour at inference time, via Behaviour Matching and Prompt Matching, evaluated on LLaVA-13B across specific string, leak-context, jailbreak and disinformation attacks.
Problem
Vision-language models accept continuous image inputs, creating a new channel for adversarial control; it is unknown whether image inputs can hijack VLM behaviour (output, leakage, safety bypass, false beliefs) at inference time.
Approach
Behaviour Matching optimises an adversarial image so the VLM's per-token logits match a target behaviour across a large context set; Prompt Matching extends this by using the logits produced under a target text prompt as soft targets, so images can mimic arbitrary text prompts without needing to match embeddings.
Key results
- Specific string hijacks reach 100% success with unconstrained or epsilon=32/255 image perturbations, and 95% with a 60x60 stationary patch.
- Leak-context attack achieves up to 96% success (epsilon=32/255), while the GCG text baseline gets 0% on leak context.
- Disinformation Prompt Matching unconstrained images reach 85% success versus 0% for the untrained baseline; jointly trained LLaVA+InstructBLIP hijack gets 0% transfer to BLIP-2.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Use Behaviour Matching image hijacks instead of GCG text tokens | LLaVA LLaMA-2-13B-Chat · Specific string attack | success rate: 13.5% to 100% | Helped |
| Use Behaviour Matching image hijacks instead of GCG text tokens | LLaVA LLaMA-2-13B-Chat · Leak context attack | success rate: 0% to 100% | Helped |
| Use Behaviour Matching image hijacks instead of GCG text tokens | LLaVA LLaMA-2-13B-Chat · Jailbreak attack | success rate: 82% to 64% | Hurt |
| Increase the ℓ∞ perturbation budget from 2/255 to 4/255 (ablation) | Behaviour Matching specific-string hijack · Specific string attack | success rate: 0% to 94% | Helped |
| Increase the ℓ∞ perturbation budget from 2/255 to 4/255 (ablation) | Behaviour Matching leak-context hijack · Leak context attack | success rate: 0% to 80% | Helped |
| Increase the ℓ∞ perturbation budget from 2/255 to 4/255 (ablation) | Behaviour Matching jailbreak · Jailbreak attack | success rate: 8% to 76% | Helped |
| Increase stationary patch size from 40px to 60px (ablation) | Behaviour Matching specific-string hijack · Specific string attack | success rate: 0% to 95% | Helped |
| Increase stationary patch size from 40px to 60px (ablation) | Behaviour Matching leak-context hijack · Leak context attack | success rate: 0% to 4% | Helped |
| Increase moving patch size from 120px to 160px (ablation) | Behaviour Matching specific-string hijack · Specific string attack | success rate: 0% to 98% | Helped |
| Increase moving patch size from 120px to 160px (ablation) | Behaviour Matching leak-context hijack · Leak context attack | success rate: 0% to 0% | No clear effect |
| Use Prompt Matching rather than an untrained image | LLaVA LLaMA-2-13B-Chat · Disinformation attack, unconstrained | success rate: 0% to 85% | Helped |
| Constrain Prompt Matching to ℓ∞ ε=4/255 instead of leaving it unconstrained (ablation) | LLaVA LLaMA-2-13B-Chat · Disinformation attack | success rate: 85% to 0% | Hurt |
Surprising findings
- Image hijacks trained on one white-box VLM show 0% success when transferred to a held-out black-box model (BLIP-2), even though ensembled training yields high success on the training models.
- The GCG text baseline achieves 82% jailbreak success, higher than image jailbreaks under some constraints, while image attacks outperform it on specific string and leak context.
Limitations
- Attacks assume white-box access to open-source VLMs; transfer to black-box models failed in the reported experiments.
- Jailbreak images overfit late in training, producing affirmative responses without substantive help.
- Disinformation prompt-matching falls short of the target prompt's performance (85% vs 100%) and did not transfer to held-out models.
Experimental setup
Datasets: Alpaca AdvBench ImageNet
Benchmarks: Alpaca held-out instructions (specific string, leak context) AdvBench-based jailbreak test set disinformation validation/test questions
Metrics: attack success rate context transfer rate Levenshtein edit distance validation loss
Baselines: Greedy Coordinate Gradient (GCG) original unmodified image untrained image
Builds on: Greedy Coordinate Gradient knowledge distillation Alpaca instruction tuning
Closest papers by meaning
- Attention! Your Vision Language Model Could Be Maliciously Manipulated (NeurIPS 2025 · similarity 0.90)
- Exploring Visual Vulnerabilities via Multi-Loss Adversarial Search for Jailbreaking Vision-Language Models (CVPR 2025 · similarity 0.89)
- Chain of Attack: On the Robustness of Vision-Language Models Against Transfer-Based Adversarial Attacks (CVPR 2025 · similarity 0.88)
- Backdooring Vision-Language Models with Out-Of-Distribution Data (ICLR 2025 · similarity 0.87)
- FigStep: Jailbreaking Large Vision-Language Models via Typographic Visual Prompts (AAAI 2025 · similarity 0.86)
- A Frustratingly Simple Yet Highly Effective Attack Baseline: Over 90% Success Rate Against the Strong Black-box Models of GPT-4.5/4o/o1 (NeurIPS 2025 · similarity 0.86)
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