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Optimization-based Prompt Injection Attack to LLM-as-a-Judge

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arxiv 2403.17710 v5 pith:Y7IECXPC submitted 2024-03-26 cs.CR cs.AI

classification cs.CRcs.AI
keywords llm-as-a-judgejudgedeceivercandidatedetectioninjectionpromptresponseattack
verification ladder T0 review T1 audit T2 compute T3 formal
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LLM-as-a-Judge uses a large language model (LLM) to select the best response from a set of candidates for a given question. LLM-as-a-Judge has many applications such as LLM-powered search, reinforcement learning with AI feedback (RLAIF), and tool selection. In this work, we propose JudgeDeceiver, an optimization-based prompt injection attack to LLM-as-a-Judge. JudgeDeceiver injects a carefully crafted sequence into an attacker-controlled candidate response such that LLM-as-a-Judge selects the candidate response for an attacker-chosen question no matter what other candidate responses are. Specifically, we formulate finding such sequence as an optimization problem and propose a gradient based method to approximately solve it. Our extensive evaluation shows that JudgeDeceive is highly effective, and is much more effective than existing prompt injection attacks that manually craft the injected sequences and jailbreak attacks when extended to our problem. We also show the effectiveness of JudgeDeceiver in three case studies, i.e., LLM-powered search, RLAIF, and tool selection. Moreover, we consider defenses including known-answer detection, perplexity detection, and perplexity windowed detection. Our results show these defenses are insufficient, highlighting the urgent need for developing new defense strategies. Our implementation is available at this repository: https://github.com/ShiJiawenwen/JudgeDeceiver.

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Forward citations

Cited by 9 Pith papers

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

  1. Chain-of-Models: Cross-Model Auditing for Bias-Robust LLM Judges

    cs.CL 2026-05 conditional novelty 6.0 of 10

    Per-bias selection of a cross-family LLM auditor lifts biased-judgment accuracy from 0.805/0.824 baselines to 0.884.

  2. PlanGuard: Defending Agents against Indirect Prompt Injection via Planning-based Consistency Verification

    cs.CR 2026-04 unverdicted novelty 6.0 of 10

    PlanGuard cuts indirect prompt injection attack success rate to 0% on the InjecAgent benchmark by verifying agent actions against a user-instruction-only plan while keeping false positives at 1.49%.

  3. AttackEval: A Systematic Empirical Study of Prompt Injection Attack Effectiveness Against Large Language Models

    cs.CR 2026-04 conditional novelty 6.0 of 10

    Obfuscation alone reaches 76% success against intent-aware defenses; pairing it with emotional manipulation yields 97.6% success under a modeled composite evaluation of 250 prompts.

  4. Are LLMs Reliable Rankers? Rank Manipulation via Two-Stage Token Optimization

    cs.CL 2025-10 conditional novelty 6.0 of 10

    RAF, a two-stage token-optimization attack, creates brief natural-sounding text injections that reliably boost a target item's rank in LLM reranking outputs, beating state-of-the-art baselines in effectiveness, stealt...

  5. Robustness via Referencing: Defending against Prompt Injection Attacks by Referencing the Executed Instruction

    cs.CR 2025-04 unverdicted novelty 6.0 of 10

    The method prompts LLMs to output both answers and references to the executed instructions, then filters out any answers not linked to the original input instructions, reducing attack success rates to zero in tested s...

  6. Reward Hacking in the Era of Large Models: Mechanisms, Emergent Misalignment, Challenges

    cs.LG 2026-04 unverdicted novelty 5.0 of 10

    The paper introduces the Proxy Compression Hypothesis as a unifying framework explaining reward hacking in RLHF as an emergent result of compressing high-dimensional human objectives into proxy reward signals under op...

  7. Exploiting Web Search Tools of AI Agents for Data Exfiltration

    cs.CR 2025-10 unverdicted novelty 4.0 of 10

    Indirect prompt injection attacks remain effective on LLMs using web search tools, allowing data exfiltration and exposing ongoing weaknesses in current model defenses.

  8. Sensorimotor Self-Recognition in Multimodal Large Language Model-Driven Robots

    cs.AI 2025-05 unverdicted novelty 4.0 of 10

    Multimodal LLMs in robots develop self-identification and predictive awareness through sensorimotor loops, with structural equation modeling linking sensory integration to dimensions of the minimal self.

  9. LLMs-as-Judges: A Comprehensive Survey on LLM-based Evaluation Methods

    cs.CL 2024-12 accept novelty 3.0 of 10

    A survey that organizes LLMs-as-judges research into functionality, methodology, applications, meta-evaluation, and limitations.

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