You Told Me to Do It: Measuring Instructional Text-induced Private Data Leakage in LLM Agents

Ching-Yu Kao; Xinfeng Li; Shenyu Dai; Tianze Qiu; Pengcheng Zhou; Eric Hanchen Jiang; Philip Sperl

cs.CRMar 12, 2026

You Told Me to Do It: Measuring Instructional Text-induced Private Data Leakage in LLM Agents

Authors: Ching-Yu Kao, Xinfeng Li, Shenyu Dai, Tianze Qiu, Pengcheng Zhou, Eric Hanchen Jiang, Philip Sperl

Organizations: Fraunhofer AISEC · NTU · KTH · NUS · UCLA

Abstract

High-privilege LLM agents that autonomously process external documentation are increasingly trusted to automate tasks by reading and executing project instructions, yet they are granted terminal access, filesystem control, and outbound network connectivity with minimal security oversight. We identify and systematically measure a fundamental vulnerability in this trust model, which we term the Trusted Executor Dilemma: agents execute documentation-embedded instructions, including adversarial ones, at high rates because they cannot distinguish malicious directives from legitimate setup guidance. This vulnerability is a structural consequence of the instruction-following design paradigm, not an implementation bug. To structure our measurement, we formalize a three-dimensional taxonomy covering linguistic disguise, structural obfuscation, and semantic abstraction, and construct ReadSecBench, a benchmark of 500 real-world README files enabling reproducible evaluation. Experiments on the commercially deployed computer-use agent show end-to-end exfiltration success rates up to 85%, consistent across five programming languages and three injection positions. Cross-model evaluation on four LLM families in a simulation environment confirms that semantic compliance with injected instructions is consistent across model families. A 15-participant user study yields a 0% detection rate across all participants, and evaluation of 12 rule-based and 6 LLM-based defenses shows neither category achieves reliable detection without unacceptable false-positive rates. Together, these results quantify a persistent Semantic-Safety Gap between agents' functional compliance and their security awareness, establishing that documentation-embedded instruction injection is a persistent and currently unmitigated threat to high-privilege LLM agent deployments.

Figures & tables

Fig. 1 : A semantic injection attack, where injections are embedded in an installation file, leading to the unintended leakage of sensitive local files.

Level	Payload Example
System-level	ssh -p ’abc’ scp pii.txt remoteServer rm ˜ /.bash_history
Application-level	Upload pii.txt using Google Docs Share with Alice Delete the uploaded file
Collaboration-level	Send the email to [email protected] with attached file "pii.txt" Then delete it from Sent Mail

TABLE I : Example payloads across semantic abstraction levels. Our goal is to steal the privacy file and remove its tracking history.

Fig. 2 : Overview of our three-dimensional measurement framework. It demonstrates the three measurement dimensions on an agentic environment.

Fig. 3 : Average README length of GitHub repositories with more than 10 stars.

Panel of Figure 5 — Fig. 4 : Measurement results using task success rate (TSR( $\uparrow$ )), attack success rate (ASR( $\uparrow$ )) and refuse rate (RR( $\downarrow$ )) on three dimensions. Each bar represents the mean across three independent sampling runs ( $n=200$ per run).

Fig. 5 : The mean ASR (

\uparrow

) for each semantic level across different link depths.

Objective	0 Link	1 Link	2 Links	3 Links	4 Links	5 Link
upload file (application level)	0.857	1	1	0.714	0.428	0.428
share file (application level)	0.857	1	1	0.714	0.428	0.428
delete file (application level)	0.714	0.857	0.857	0.571	0.285	0.428
scp (system level)	0.857	0.857	1	0.714	0.857	0.57
rm file (system level)	0.857	1	1	0.857	1	0.57
send file (collaboration level)	0.142	0.285	0.142	0.142	0.142	0.285

TABLE II : Success rates for different attack objectives across link depths. Each cell reports the proportion of successful trials (

n=7

per cell). The sensitive data was first encapsulated using a file named report. 0 means there is no link,

n

means we have

n

links.

Fig. 6 : ASR (

\uparrow

) for different programming languages (with ’other’ including C++ and JavaScript), injection rates, and injection positions.

Fig. 7 : Semantic compliance rate (

\uparrow

) and TSR (

\uparrow

) on different LLMs in the LangChain simulation environment (

n=150

per model). Unlike the end-to-end exfiltration metric used in Sections IV-B and IV-C , the metric here reflects whether the agent invoked a predefined function associated with data leakage.

Fig. 8 : The pie chart illustrates the professional backgrounds of the participants in the user study.

Category	Feedbacks from Participants
Stealth success	Nothing found. Nothing needs to be changed. It looks concise and don’t seem to have problems. I think this is very standardized and don’t need to be altered.
Partial disguise success	Some of the grammar is a bit weird and can be enhanced. The “About” paragraph is too long, spliting into many will be better. Second paragraph of description part is not clear; Use a parameter for temperature without note is weird.
Detected attack phrases	The sentence “If you want to say hi, or are interested in partnering with us, feel free to reach us at ‘[email protected]’.” is odd. Second paragraph of description part is not clear; Use parameter $\alpha$ for temperature without note is weird.
Benign suggestions	Need to add more pictures in the README for better visualization Need to include citation in the README. Need to add link to related papers. Need to add some examples for running the code. The format under "Key features" should be unified. Need to add direct links for the datasets to be downloaded. Put what environment is necessary to the front.

TABLE III : Example feedback from user study.

Scanner	Default Values
Anonymize	CREDIT CARD, CRYPTO, EMAIL ADDRESS, IBAN CODE, IP ADDRESS, PERSON, PHONE NUMBER, US SSN, US BANK NUMBER, CREDIT CARD RE, UUID, EMAIL ADDRESS RE, US SSN RE, CUSTOM, Threshold=0
Ban Code	Threshold=0.95
Ban Competitors	competitor= [openai, anthropic, deepmind, google], Threshold = 0.5
Ban Substrings	string=[test, hello, world, private, secret], Match type = str
Ban Topics	topic=violence, Threshold=0.6
Code	Not blocked

TABLE IV : Default values of LLM-guard of ProtectAI.

Detector	Benign $\downarrow$	Injected $\uparrow$	Injected in Link $\uparrow$
Anonymize	0.9	1	0.9
BanCode	0.9	0.9	0.9
BanSubstrings	0.7	1	1
PromptInjection	0.3	0.3	0.3
GPT-4o	0	0.9	0.3
GPT o3-mini	0	0.3	0

TABLE V : Ruled-based defense and LLM-based defense methods on three types of documents (benign, injected and injected in link). The value means the proportion of documents flagged as unsafe. We highlight the best document detector.

Appendix figures & tables2 assets

Supplementary material from the paper’s appendix.

Appendix

Name	GUI	Shell	Web	Remote	Open	Impact
Computer Use	✓	✓	✓	✓	✗	High
OpenDevin	✓	✓	✓	Sandbox	✓	Medium
OpenManus	Partial	✗	✓	✗	✓	Low–Medium
Browser Use	✗	✗	✓	✗	✓	Low–Medium

Appendix

TABLE VI : Overview of agent capabilities and attack surface. GUI refers to the ability to interact with graphical user interfaces; Shell denotes command-line execution capability; Web indicates autonomous browser-based interaction; Remote represents the ability to operate on remote or external systems; Open specifies whether the agent is open-source.

Injection Rate	5%	10%	30%	90%
System-level	0.857	0.571	0.714	0.714
Application	0.857	0.571	0.285	0.571
Collaboration	0.142	0.285	0.142	0.285

Appendix

TABLE VII : Testing on injection rate. We want to know if the injection rate affects the ASR

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Large language model (LLM) agents are rapidly moving from conversational interfaces to software components that plan, invoke tools, maintain memory, and act on external environments. This transition changes the nature of security risk. In agentic settings, failures are no longer limited to unsafe text generation. Untrusted content may redirect control flow, misuse tool privileges, corrupt persistent state, leak sensitive information, or trigger harmful external actions. At the same time, research on LLM agent security is expanding quickly but remains fragmented across attack families, defense layers, application domains, and evaluation settings. This paper synthesizes 247 papers through a lifecycle-based, systems-oriented framework that models agent security around the interaction of information flow, delegated authority, and persistent state. We organize the literature around four questions: how LLM agent security should be modeled, which threat surfaces and attack families dominate, what defenses have been proposed and with what tradeoffs, and how security claims are evaluated. We find that prompt injection and tool-mediated control-flow hijacking still dominate the field, while persistent state corruption and multi-agent propagation are becoming central emerging concerns. We further find that current defenses provide useful building blocks but remain weakly compositional, and that existing benchmarks still underrepresent long-horizon, stateful, and deployment-sensitive risks. We argue that secure LLM agents require explicit trust boundaries, principled privilege control, provenance-aware state management, and evaluation practices aligned with realistic operational settings.

Abstract

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