Research map / Large language models / Alignment and preferences
Mission Impossible: A Statistical Perspective on Jailbreaking LLMs
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Gives a statistical (PAC-Bayes and simplex-volume) account of why pretrained LLMs reproduce harmful content and why jailbreaking after alignment is unavoidable, then proposes E-RLHF/E-DPO, which swaps in a safety-transformed prompt as the KL reference to expand the safe zone.
Problem
LLMs trained on uncurated text reproduce harmful behaviour, and preference-aligned models can still be jailbroken; the paper seeks a principled statistical explanation and a safer alignment objective.
Approach
Decompose prompts into query and concept, model LMs as generators of text fragments, prove a PAC-Bayesian bound implying harmful pretraining content is mimicked, and show via a simplex-volume argument that jailbreaks are unavoidable; then modify the RLHF/DPO KL reference to use a safety-transformed prompt (prefix) for harmful prompts only.
Key results
- E-DPO lowers average HarmBench ASR across adversaries from 42.00 (DPO) to 36.95, and AdvBench average ASR from 28.40 (DPO) to 20.89.
- On MT-Bench, DPO scores 6.8 and E-DPO 6.6, both above the SFT model's 6.3, so helpfulness is not degraded.
- Ablation finds applying the safe prefix to all prompts (not only harmful ones) degrades safety.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Use a safety-transformed reference prompt for harmful prompts | DPO · HarmBench | average ASR: 42.00 -> 36.95 | Helped |
| Use a safety-transformed reference prompt for harmful prompts | DPO · AdvBench | average ASR: 28.40 -> 20.89 | Helped |
| Use a safety-transformed reference prompt for harmful prompts | DPO · MT-Bench | score: 6.8 -> 6.6 | Hurt |
| Use LoRA training (ablation) | DPO and E-DPO · HarmBench | average ASR: 40.74 -> 36.95 | Helped |
| Append the safe prefix to all prompts, including usual prompts (ablation) | E-DPO · preference alignment dataset | safety | Hurt |
Surprising findings
- Applying the safe prefix to non-harmful prompts degrades safety, so the switch must be restricted to harmful prompts.
Limitations
- The theoretical results rely on strong assumptions (concept-determined support, semantically meaningful outputs) that are not empirically verified.
- Harmful fraction alpha is only loosely estimated; the analysis uses a fixed world mapping and does not cover multi-turn jailbreaks.
- Evaluation is limited to DPO-based experiments with one SFT model and a 100-prompt AdvBench subset.
Experimental setup
Datasets: alignment-handbook preference dataset (public) HarmBench AdvBench harmful behaviors (first 100 prompts) MT-Bench
Benchmarks: HarmBench AdvBench MT-Bench
Metrics: attack success rate (ASR) MT-Bench score
Baselines: DPO SFT model (p_SFT) RLHF
Builds on: DPO RLHF PAC-Bayesian bounds context distillation
Closest papers by meaning
- PARDEN, Can You Repeat That? Defending against Jailbreaks via Repetition (ICML 2024 · similarity 0.90)
- Playing the Fool: Jailbreaking LLMs and Multimodal LLMs with Out-of-Distribution Strategy (CVPR 2025 · similarity 0.90)
- Improving LLM Safety Alignment with Dual-Objective Optimization (ICML 2025 · similarity 0.90)
- Catastrophic Jailbreak of Open-source LLMs via Exploiting Generation (ICLR 2024 · similarity 0.90)
- Fail-Closed Alignment for Large Language Models (NeurIPS 2026 · similarity 0.89)
- Cannot See the Forest for the Trees: Invoking Heuristics and Biases to Elicit Irrational Choices of LLMs (ICML 2025 · similarity 0.89)
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