Cited by 3Adversarial Robustness in Machine LearningInformation Retrieval and Search BehaviorTopic Modeling

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

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Xing, Tiancheng, Li, Jerry, Du, Yixuan, Hu, Xiyang·2026·Proceedings of the 64th Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers)

Abstract

Large language models (LLMs) are increasingly used as rerankers in information retrieval, yet their ranking behavior can be steered by small, natural-sounding prompts.To expose this vulnerability, we present Rank Anything First (RAF), a two-stage token optimization method that crafts concise textual perturbations to consistently promote a target item in LLMgenerated rankings while remaining hard to detect.Stage 1 uses Greedy Coordinate Gradient to shortlist candidate tokens at the current position by combining the gradient of the rank-target with a readability score; Stage 2 evaluates those candidates under exact ranking and readability losses using an entropy-based dynamic weighting scheme, and selects a token via temperature-controlled sampling.RAF generates ranking-promoting prompts tokenby-token, guided by dual objectives: maximizing ranking effectiveness and preserving linguistic naturalness.Experiments across multiple LLMs show that RAF significantly boosts the rank of target items using naturalistic language, with greater robustness than existing methods in both promoting target items and maintaining naturalness.These findings underscore a critical security implication: LLMbased reranking is inherently susceptible to adversarial manipulation, raising new challenges for the trustworthiness and robustness of modern retrieval systems.

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Cited by

Sorted by citations

Authors
Xing, T., Li, J., Du, Y., & Hu, X.
Affiliations
  • National University of Singapore (SG)
  • University of Southern California (US)
  • Georgetown University (US)
  • Arizona State University (US)
Venue
Proceedings of the 64th Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers)
Published
2026
Pages
9120-9132
ISSN
0736-587X (ISSN-L)
OpenAlex
W4415317037
Cited by
3
References
0
Citations by year
2026: 3
FWCI
12.69
Type
conference paper
Language
en
Open access
Licence
cc-by
Locations
  • Proceedings of the conference - Association for Computational Linguistics. Meeting (publishedVersion, cc-by)
  • arXiv (Cornell University) (submittedVersion)
  • arXiv (Cornell University)
Funders
National Science Foundation (2137603, 2138259, 2138296, 2138307, 2138286)
Topics
  • Physical Sciences › Computer Science › Artificial Intelligence › Adversarial Robustness in Machine Learning
  • Physical Sciences › Computer Science › Information Systems › Information Retrieval and Search Behavior
  • Physical Sciences › Computer Science › Artificial Intelligence › Topic Modeling
Keywords
large language models, re-ranking, information retrieval, two-stage optimization, prompt engineering, readability, adversarial robustness, LLM security

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