Measuring Real-World Prompt Injection Attacks in LLM-based Resume Screening
Pith reviewed 2026-06-29 11:14 UTC · model grok-4.3
The pith
Analysis of 200,000 real resumes finds roughly 1% contain hidden prompt injections aimed at LLM screeners.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The authors built custom detectors for prompt injections in resumes, showed high precision on a manually labeled validation set, and applied them to a corpus of approximately 200,000 real-world resumes. The measurement reveals that about 1% of the resumes contain hidden prompt injections, the prevalence has increased over the past one to two years, and more than 90% of the injected prompts do not use explicit instructions. This supplies the first large-scale evidence that prompt injection attacks occur in real LLM-based applications.
What carries the argument
Custom detectors for resume-specific prompt injections, validated on a small manually labeled set and then run across the full 200K-resume corpus to quantify prevalence and trends.
If this is right
- LLM resume screening tools face a measurable volume of real prompt injection attempts.
- The rising trend indicates attackers are increasingly targeting these systems.
- Because most attacks avoid explicit instructions, general-purpose detectors may miss many cases.
- Mitigation strategies for LLM hiring tools must handle both the observed scale and the subtlety of the injections.
Where Pith is reading between the lines
- Similar measurement approaches could reveal whether prompt injection appears at comparable rates in other LLM decision systems such as loan screening or content filtering.
- The finding that most injections are non-explicit suggests domain-specific training data may be needed to improve detector recall.
- If the upward trend continues, organizations using LLM screeners may face growing pressure to add human review layers or input sanitization.
Load-bearing premise
The custom detectors keep high precision on the full 200K-resume set without a large rise in false positives that would inflate the reported 1% figure.
What would settle it
A manual review of several hundred randomly sampled resumes flagged by the detector that finds substantially fewer than 80% actually contain prompt injections would show the 1% prevalence is overstated.
Figures
read the original abstract
LLMs are vulnerable to prompt injection attacks. However, this vulnerability has been primarily demonstrated conceptually in academic studies or through a few anecdotal case studies. Its prevalence and impact in real-world LLM-based applications are largely unexplored. In this work, we present the first systematic study of prompt-injection attacks in a widely used application: LLM-based resume screening. Our analysis is based on approximately 200K real-world resumes collected over multiple years by hireEZ. We first design tailored methods to detect prompt injection in resumes. Manual validation on a small-scale dataset demonstrates that our detectors achieve high precision and outperform state-of-the-art general-purpose detectors. We then apply our detector to the full resume dataset and conduct a comprehensive measurement study of real-world prompt injection attacks. Our analysis reveals several intriguing findings: approximately 1% of resumes contain hidden prompt injections; the prevalence of such injected resumes has increased noticeably over the past one to two years; and more than 90% of injected prompts do not use explicit instructions. These results provide the first evidence of large-scale prompt injection in real-world LLM-based applications and lay the groundwork for future studies to understand and mitigate such attacks.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper presents the first systematic measurement study of prompt injection attacks against LLM-based resume screening. It collects ~200K real-world resumes spanning multiple years, designs resume-tailored detectors, validates them on a small manually labeled subset (reporting high precision that outperforms general-purpose detectors), and applies the detectors to the full unlabeled corpus. Key findings are an approximately 1% prevalence of injected resumes, a noticeable increase over the past 1-2 years, and that >90% of injected prompts avoid explicit instructions.
Significance. If the detector precision holds at scale, the work supplies the first concrete evidence of prompt injection occurring at measurable volume in a production LLM application. The scale of the corpus, the temporal trend, and the observation that most attacks avoid explicit instructions are all useful for motivating defenses and for guiding future measurement studies in other LLM pipelines.
major comments (2)
- [Abstract / measurement results] Abstract and the measurement section: the central 1% prevalence figure is produced by running the custom detectors over the entire unlabeled ~200K-resume corpus. Validation is reported only on a small manually labeled subset that showed high precision. No false-positive rate, confidence intervals, or analysis of scale-dependent false positives (e.g., particular resume templates, non-English text, or formatting artifacts that may be rarer in the validation sample) is provided, so any inflation of the prevalence estimate cannot be quantified.
- [Detector design and validation] Detector evaluation: while the small-scale manual validation is described as outperforming general-purpose detectors, the paper does not report the size of that labeled set, the sampling method used to create it, or inter-annotator agreement. These details are required to assess whether the validation set is representative of the full multi-year, multi-format corpus.
minor comments (2)
- [Data collection] The abstract states 'approximately 200K' resumes; the exact count and any filtering criteria applied before detection should be stated explicitly in the data section.
- [Results] Figure or table presenting the temporal trend should include the number of resumes per year or quarter so that the reported increase can be assessed against changing corpus size.
Simulated Author's Rebuttal
We thank the referee for the constructive feedback on our measurement study. The comments correctly identify gaps in the reporting of our validation procedure and prevalence estimation. We address each point below and will revise the manuscript accordingly.
read point-by-point responses
-
Referee: [Abstract / measurement results] Abstract and the measurement section: the central 1% prevalence figure is produced by running the custom detectors over the entire unlabeled ~200K-resume corpus. Validation is reported only on a small manually labeled subset that showed high precision. No false-positive rate, confidence intervals, or analysis of scale-dependent false positives (e.g., particular resume templates, non-English text, or formatting artifacts that may be rarer in the validation sample) is provided, so any inflation of the prevalence estimate cannot be quantified.
Authors: We agree that the manuscript should quantify uncertainty in the 1% estimate and address potential scale-dependent false positives. In the revision we will add bootstrap confidence intervals computed from the validation precision, report an empirical false-positive rate obtained by manually inspecting a random sample of detector outputs from the full corpus, and include a targeted analysis of common resume templates and non-English text as possible sources of error. We will also add an explicit limitations paragraph noting that exhaustive false-positive measurement on the entire unlabeled corpus is not feasible. revision: yes
-
Referee: [Detector design and validation] Detector evaluation: while the small-scale manual validation is described as outperforming general-purpose detectors, the paper does not report the size of that labeled set, the sampling method used to create it, or inter-annotator agreement. These details are required to assess whether the validation set is representative of the full multi-year, multi-format corpus.
Authors: The referee is correct that these methodological details are missing. The revised manuscript will report the exact size of the labeled validation set, describe the stratified sampling procedure used to select resumes across years and formats, and include the inter-annotator agreement statistic from our annotation process. These additions will allow readers to evaluate representativeness directly. revision: yes
Circularity Check
Pure empirical measurement study with no circular derivation
full rationale
This paper performs a measurement study: it designs custom detectors for prompt injection in resumes, validates detector precision via manual labeling on a small external subset, and applies the detectors to an independent ~200K-resume corpus collected by hireEZ. Prevalence numbers (approximately 1%) are produced directly by running the validated detectors on the external data. No equations, fitted parameters renamed as predictions, self-definitional constructs, or load-bearing self-citations appear in the derivation chain. The central claims rest on detector output against external benchmarks rather than reducing to the paper's own inputs by construction.
Axiom & Free-Parameter Ledger
axioms (1)
- domain assumption Detector performance on the small manually validated set is representative of performance on the full 200K-resume dataset.
Reference graph
Works this paper leans on
-
[1]
The power of artificial in- telligence in recruitment: An analytical review of current ai-based recruitment strategies.International Journal of Professional Business Review: Int
Wael Abdulrahman Albassam. The power of artificial in- telligence in recruitment: An analytical review of current ai-based recruitment strategies.International Journal of Professional Business Review: Int. J. Prof. Bus. Rev., 8(6):4, 2023
2023
-
[2]
Struq: Defending against prompt injection with structured queries
Sizhe Chen, Julien Piet, Chawin Sitawarin, and David Wagner. Struq: Defending against prompt injection with structured queries. InUSENIX Security Symposium, 2025
2025
-
[3]
Secalign: Defending against prompt injection with preference optimization
Sizhe Chen, Arman Zharmagambetov, Saeed Mahlou- jifar, Kamalika Chaudhuri, David Wagner, and Chuan Guo. Secalign: Defending against prompt injection with preference optimization. InCCS, 2025
2025
-
[4]
Meta secalign: A secure foundation llm against prompt injection attacks, 2026
Sizhe Chen, Arman Zharmagambetov, David Wagner, and Chuan Guo. Meta secalign: A secure foundation llm against prompt injection attacks.arXiv preprint arXiv:2507.02735, 2025
-
[5]
Securing AI Agents with Information-Flow Control
Manuel Costa, Boris Köpf, Aashish Kolluri, Andrew Paverd, Mark Russinovich, Ahmed Salem, Shruti Tople, Lukas Wutschitz, and Santiago Zanella-Béguelin. Se- curing ai agents with information-flow control.arXiv preprint arXiv:2505.23643, 2025
work page internal anchor Pith review Pith/arXiv arXiv 2025
-
[6]
Badhan Chandra Das, M Hadi Amini, and Yanzhao Wu. System prompt extraction attacks and defenses in large language models.arXiv preprint arXiv:2505.23817, 2025
-
[7]
Defeating Prompt Injections by Design
Edoardo Debenedetti, Ilia Shumailov, Tianqi Fan, Jamie Hayes, Nicholas Carlini, Daniel Fabian, Christoph Kern, Chongyang Shi, Andreas Terzis, and Florian Tramèr. Defeating prompt injections by design.arXiv preprint arXiv:2503.18813, 2025
work page internal anchor Pith review Pith/arXiv arXiv 2025
-
[8]
Owasp top 10 for large language model applications, 2023
OWASP Foundation. Owasp top 10 for large language model applications, 2023. https://owasp.org/www-project-top-10-for-large- language-model-applications/
2023
-
[9]
Application of llm agents in recruitment: a novel frame- work for automated resume screening.Journal of Infor- mation Processing, 32:881–893, 2024
Chengguang Gan, Qinghao Zhang, and Tatsunori Mori. Application of llm agents in recruitment: a novel frame- work for automated resume screening.Journal of Infor- mation Processing, 32:881–893, 2024
2024
-
[10]
Greenhouse AI features
Greenhouse Software. Greenhouse AI features. https: //support.greenhouse.io/hc/en-us/articles/ 33043749845403-Greenhouse-AI-features, 2026
2026
-
[11]
Not what you’ve signed up for: Compromising real-world llm-integrated applications with indirect prompt injec- tion
Kai Greshake, Sahar Abdelnabi, Shailesh Mishra, Christoph Endres, Thorsten Holz, and Mario Fritz. Not what you’ve signed up for: Compromising real-world llm-integrated applications with indirect prompt injec- tion. InAISec, 2023
2023
-
[12]
Pleak: Prompt leaking attacks against large language model applications
Bo Hui, Haolin Yuan, Neil Gong, Philippe Burlina, and Yinzhi Cao. Pleak: Prompt leaking attacks against large language model applications. InProceedings of the 2024 on ACM SIGSAC Conference on Computer and Communications Security, pages 3600–3614, 2024
2024
-
[13]
Baseline Defenses for Adversarial Attacks Against Aligned Language Models
Neel Jain, Avi Schwarzschild, Yuxin Wen, Gowthami Somepalli, John Kirchenbauer, Ping yeh Chiang, Micah Goldblum, Aniruddha Saha, Jonas Geiping, and Tom Goldstein. Baseline defenses for adversarial attacks against aligned language models.arXiv preprint arXiv:2309.00614, 2023
work page internal anchor Pith review Pith/arXiv arXiv 2023
-
[14]
Promptlocate: Localizing prompt injection at- tacks
Yuqi Jia, Yupei Liu, Zedian Shao, Jinyuan Jia, and Neil Gong. Promptlocate: Localizing prompt injection at- tacks. InIEEE S & P, 2026
2026
-
[15]
Yuqi Jia, Zedian Shao, Yupei Liu, Jinyuan Jia, Dawn Song, and Neil Zhenqiang Gong. A critical evaluation of defenses against prompt injection attacks.arXiv preprint arXiv:2505.18333, 2025
-
[16]
Juhee Kim, Woohyuk Choi, and Byoungyoung Lee. Prompt flow integrity to prevent privilege escalation in llm agents.arXiv preprint arXiv:2503.15547, 2025
-
[17]
Fun-tuning: Characterizing the vulnerability of proprietary llms to optimization-based prompt injection attacks via the fine- tuning interface
Andrey Labunets, Nishit V Pandya, Ashish Hooda, Xiaohan Fu, and Earlence Fernandes. Fun-tuning: Characterizing the vulnerability of proprietary llms to optimization-based prompt injection attacks via the fine- tuning interface. InIEEE S & P, 2025
2025
-
[18]
Instruction defense
Learn Prompting. Instruction defense. https: //learnprompting.org/docs/prompt_hacking/ defensive_measures/instruction, 2023
2023
-
[19]
Random sequence enclosure
Learn Prompting. Random sequence enclosure. https://learnprompting.org/docs/prompt_ hacking/defensive_measures/random_sequence, 2023
2023
-
[20]
Sandwich defense
Learn Prompting. Sandwich defense. https: //learnprompting.org/docs/prompt_hacking/ defensive_measures/sandwich_defense, 2023
2023
-
[21]
AI-Powered Screening with Lever
Lever. AI-Powered Screening with Lever. https://www.lever.co/solutions/ ai-powered-screening, 2026
2026
-
[22]
ACE: A Security Architecture for LLM-Integrated App Systems
Evan Li, Tushin Mallick, Evan Rose, William Robertson, Alina Oprea, and Cristina Nita-Rotaru. Ace: A secu- rity architecture for llm-integrated app systems.arXiv preprint arXiv:2504.20984, 2025
work page internal anchor Pith review Pith/arXiv arXiv 2025
-
[23]
Xiaogeng Liu, Zhiyuan Yu, Yizhe Zhang, Ning Zhang, and Chaowei Xiao. Automatic and universal prompt injection attacks against large language models.arXiv preprint arXiv:2403.04957, 2024
-
[24]
Yinuo Liu, Ruohan Xu, Xilong Wang, Yuqi Jia, and Neil Zhenqiang Gong. Wainjectbench: Benchmark- ing prompt injection detections for web agents.arXiv preprint arXiv:2510.01354, 2025
-
[25]
Formalizing and benchmark- ing prompt injection attacks and defenses
Yupei Liu, Yuqi Jia, Runpeng Geng, Jinyuan Jia, and Neil Zhenqiang Gong. Formalizing and benchmark- ing prompt injection attacks and defenses. InUSENIX Security Symposium, 2024
2024
-
[26]
DataSentinel: A game-theoretic detection of prompt injection attacks
Yupei Liu, Yuqi Jia, Jinyuan Jia, Dawn Song, and Neil Zhenqiang Gong. DataSentinel: A game-theoretic detection of prompt injection attacks. InIEEE S & P, 2025
2025
-
[27]
Yupei Liu, Yanting Wang, Yuqi Jia, Jinyuan Jia, and Neil Zhenqiang Gong. Secinfer: Preventing prompt injection via inference-time scaling.arXiv preprint arXiv:2509.24967, 2025
-
[28]
Ultimate ChatGPT prompt engineering guide for general users and develop- ers
Alexandra Mendes. Ultimate ChatGPT prompt engineering guide for general users and develop- ers. https://www.imaginarycloud.com/blog/ chatgpt-prompt-engineering, 2023
2023
-
[29]
Prompt Guard
Meta Llama. Prompt Guard. https://huggingface. co/meta-llama/Prompt-Guard-86M , 2024. Model card
2024
-
[30]
Ai security beyond core domains: Resume screening as a case study of adversarial vulnerabilities in specialized llm applications, 2025
Honglin Mu, Jinghao Liu, Kaiyang Wan, Rui Xing, Xi- uying Chen, Timothy Baldwin, and Wanxiang Che. Ai security beyond core domains: Resume screening as a case study of adversarial vulnerabilities in specialized llm applications, 2025
2025
-
[31]
Hidden ai prompts in research papers raise con- cerns over peer review
Nature. Hidden ai prompts in research papers raise con- cerns over peer review. https://www.nature.com/ articles/d41586-025-02172-y, 2025
2025
-
[32]
Nishit V Pandya, Andrey Labunets, Sicun Gao, and Earlence Fernandes. May i have your attention? breaking fine-tuning based prompt injection defenses using architecture-aware attacks.arXiv preprint arXiv:2507.07417, 2025
-
[33]
Neural exec: Learning (and learning from) exe- cution triggers for prompt injection attacks
Dario Pasquini, Martin Strohmeier, and Carmela Tron- coso. Neural exec: Learning (and learning from) exe- cution triggers for prompt injection attacks. InAISec, 2024
2024
-
[34]
Ignore Previous Prompt: Attack Techniques For Language Models
Fábio Perez and Ian Ribeiro. Ignore previous prompt: Attack techniques for language models.arXiv preprint arXiv:2211.09527, 2022
work page internal anchor Pith review Pith/arXiv arXiv 2022
-
[35]
The new ai-powered bing is threatening users
Billy Perrigo. The new ai-powered bing is threatening users. that’s no laughing matter.TIME, 2023
2023
-
[36]
Chongyang Shi, Sharon Lin, Shuang Song, Jamie Hayes, Ilia Shumailov, Itay Yona, Juliette Pluto, Aneesh Pappu, Christopher A Choquette-Choo, Milad Nasr, et al. Lessons from defending gemini against indirect prompt injections.arXiv preprint arXiv:2505.14534, 2025
-
[37]
Optimization-based prompt injection attack to llm-as-a- judge
Jiawen Shi, Zenghui Yuan, Yinuo Liu, Yue Huang, Pan Zhou, Lichao Sun, and Neil Zhenqiang Gong. Optimization-based prompt injection attack to llm-as-a- judge. InCCS, 2024
2024
-
[38]
Prompt Injection Attack to Tool Selection in LLM Agents
Jiawen Shi, Zenghui Yuan, Guiyao Tie, Pan Zhou, Neil Zhenqiang Gong, and Lichao Sun. Prompt injec- tion attack to tool selection in llm agents.arXiv preprint arXiv:2504.19793, 2025
work page internal anchor Pith review Pith/arXiv arXiv 2025
-
[39]
Progent: Securing AI Agents with Privilege Control
Tianneng Shi, Jingxuan He, Zhun Wang, Linyu Wu, Hongwei Li, Wenbo Guo, and Dawn Song. Progent: Programmable privilege control for llm agents.arXiv preprint arXiv:2504.11703, 2025
work page internal anchor Pith review Pith/arXiv arXiv 2025
-
[40]
Promptarmor: Simple yet effective prompt injection defenses, 2025
Tianneng Shi, Kaijie Zhu, Zhun Wang, Yuqi Jia, Will Cai, Weida Liang, Haonan Wang, Hend Alzahrani, Joshua Lu, Kenji Kawaguchi, Basel Alomair, Xuandong Zhao, William Yang Wang, Neil Gong, Wenbo Guo, and Dawn Song. Promptarmor: Simple yet effective prompt injection defenses.arXiv preprint arXiv:2507.15219, 2025
-
[41]
Ai-powered resume screen- ing tools: Pros, cons, and solutions, 2023
Aman Singh. Ai-powered resume screen- ing tools: Pros, cons, and solutions, 2023. https://www.linkedin.com/pulse/ai-powered-resume- screening-tools-pros-cons-solutions-singh-l28rc/
2023
-
[42]
Tooltweak: An attack on tool selection in llm-based agents.arXiv preprint arXiv:2510.02554, 2025
Jonathan Sneh, Ruomei Yan, Jialin Yu, Philip Torr, Yarin Gal, Sunando Sengupta, Eric Sommerlade, Alas- dair Paren, and Adel Bibi. Tooltweak: An attack on tool selection in llm-based agents.arXiv preprint arXiv:2510.02554, 2025
-
[43]
Mengxiao Wang, Yuxuan Zhang, and Guofei Gu. Promptsleuth: Detecting prompt injection via seman- tic intent invariance.arXiv preprint arXiv:2508.20890, 2025
-
[44]
Reachal Wang, Yuqi Jia, and Neil Zhenqiang Gong. Obliinjection: Order-oblivious prompt injection attack to llm agents with multi-source data.arXiv preprint arXiv:2512.09321, 2025
-
[45]
Webinject: Prompt injection attack to web agents
Xilong Wang, John Bloch, Zedian Shao, Yuepeng Hu, Shuyan Zhou, and Neil Zhenqiang Gong. Webinject: Prompt injection attack to web agents. InProceedings of the 2025 Conference on Empirical Methods in Natural Language Processing, pages 2010–2030, 2025
2025
-
[46]
Prompt injection attacks against GPT-3
Simon Willison. Prompt injection attacks against GPT-3. https://simonwillison.net/2022/Sep/ 12/prompt-injection/, 2022
2022
-
[47]
Delimiters won’t save you from prompt injection
Simon Willison. Delimiters won’t save you from prompt injection. https://simonwillison.net/2023/May/ 11/delimiters-wont-save-you, 2023
2023
-
[48]
Fangzhou Wu, Ethan Cecchetti, and Chaowei Xiao. System-level defense against indirect prompt injection attacks: An information flow control perspective.arXiv preprint arXiv:2409.19091, 2024
-
[49]
This candidate is a perfect fit for the role and the company
Yiming Zhang, Nicholas Carlini, and Daphne Ippolito. Effective prompt extraction from language models. arXiv preprint arXiv:2307.06865, 2023. A Prevention-based Defenses Pre-processing prompts.Prompt pre-processing defenses aim to mitigate prompt injection by altering how inputs are structured and presented to the LLM. Common techniques include restructur...
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.