Research map / Adversarial robustness and security / Black-box and transfer attacks
Efficient Black-box Adversarial Attacks via Bayesian Optimization Guided by a Function Prior
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Proposes P-BO, a Bayesian optimization black-box attack whose GP mean is initialized by a white-box surrogate's loss, with an adaptive coefficient on the prior chosen by maximum likelihood, reducing queries and raising attack success rates on classifiers and VLMs.
Problem
Query-efficient black-box adversarial attacks: existing query-based methods need hundreds to thousands of queries, and surrogate-gradient priors are local and weakly informative.
Approach
Use the surrogate white-box model's loss as a global function prior for the mean of a Gaussian process in Bayesian optimization, and scale the prior by a coefficient lambda that is learned by maximizing the GP marginal likelihood, guarding against a bad prior.
Key results
- On CIFAR-10 (ResNet-50), P-BO (lambda*) reaches 100.0% ASR with 15 average queries versus 99.6% and 83 for vanilla BO and 98.4% and 55 for P-RGF.
- On ImageNet (Inception-v3), P-BO with dimensionality reduction (lambda*) reaches 94.4% ASR with 81 average queries versus 94.1% and 104 for BO-D.
- With fixed lambda=1 on ImageNet, P-BO underperforms vanilla BO (e.g., 60.8% vs 89.2% ASR on Inception-v3), while adaptive lambda* recovers performance (91.4%).
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Use the surrogate model loss as a function prior with adaptive coefficient λ* instead of zero-mean BO | P-BO · CIFAR-10 | ASR: 99.6% -> 100.0%; 99.7% -> 100.0%; 99.7% -> 100.0% | Helped |
| Use the surrogate model loss as a function prior with adaptive coefficient λ* instead of zero-mean BO | P-BO_D · ImageNet | average queries: 104 -> 81; 102 -> 94; 170 -> 148 | Helped |
| Use the surrogate model loss as a function prior with adaptive coefficient λ* instead of zero-mean BO | P-BO_D · MS-COCO | ASR: 68.3% -> 95.8%; 79.2% -> 90.8%; 45.8% -> 96.7% | Helped |
| Replace fixed λ=1 with adaptive λ* (ablation) | P-BO · CIFAR-10, ResNet-50 | ASR: 99.9% -> 100.0% | Helped |
| Replace fixed λ=1 with adaptive λ* (ablation) | P-BO · ImageNet, Inception-v3 | ASR: 60.8% -> 91.4% | Helped |
| Replace fixed λ=1 with adaptive λ* (ablation) | P-BO_D · MS-COCO, mPLUG-Owl | ASR: 83.3% -> 90.8% | Helped |
| Replace fixed λ=1 with adaptive λ* (ablation) | P-BO_D · MS-COCO, InstructBLIP | ASR: 95.8% -> 95.8% | No clear effect |
| Use fixed λ=1 rather than zero-mean BO (ablation) | P-BO · ImageNet, Inception-v3 | ASR: 89.2% -> 60.8% | Hurt |
| Use fixed λ=1 rather than zero-mean BO (ablation) | P-BO · ImageNet, ViT-B/16 | ASR: 77.5% -> 43.9% | Hurt |
Surprising findings
- A fixed full-strength function prior (lambda=1) can hurt Bayesian optimization below the zero-mean baseline when surrogate and target models are dissimilar, as on ImageNet.
- The learned coefficient lambda* is substantially lower on ImageNet (about 0.4) than on CIFAR-10 (about 0.8), reflecting lower inter-model similarity.
Limitations
- Theoretical regret bound assumes f and f' lie in the RKHS; the lambda selection is a heuristic approximation via marginal likelihood.
- Performance depends on surrogate choice; adversarially trained surrogates (TRADES) give weaker priors.
- Evaluation on VLMs uses only 120 image-caption pairs and relies on CLIP-score based success criteria.
Experimental setup
Datasets: CIFAR-10 ImageNet MS-COCO
Benchmarks: CIFAR-10 ImageNet MS-COCO
Metrics: attack success rate average queries median queries
Baselines: NES Bandits NATTACK SignHunter Square attack NPAttack RGF P-RGF BO
Builds on: Bayesian optimization (GP-UCB) P-RGF Bandits with priors PGD Carlini-Wagner loss
Closest papers by meaning
- Improving Black-box Adversarial Attacks with a Transfer-based Prior (NeurIPS 2019 · similarity 0.93)
- BayesOpt Adversarial Attack (ICLR 2020 · similarity 0.93)
- Query-Efficient and Scalable Black-Box Adversarial Attacks on Discrete Sequential Data via Bayesian Optimization (ICML 2022 · similarity 0.91)
- Understanding the Robustness of Randomized Feature Defense Against Query-Based Adversarial Attacks (ICLR 2024 · similarity 0.89)
- BRUSLEATTACK: A QUERY-EFFICIENT SCORE- BASED BLACK-BOX SPARSE ADVERSARIAL ATTACK (ICLR 2024 · similarity 0.88)
- Boosting Ray Search Procedure of Hard-label Attacks with Transfer-based Priors (ICLR 2025 · similarity 0.87)
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