CPInj: Uncovering Prompt Injection Risks in Textual Collaborative Prompt Optimization
Textual Collaborative Prompt Optimization (TCPO) extends TextGrad (Yuksekgonul et al., 2025) to a decentralized setting by allowing multiple clients to jointly improve prompts for large language models (LLMs) while keeping their data locally. Its reliance on free-form textual updating and aggregation introduces a new and largely unexplored attack surface, i.e., malicious instructions can be injected into local prompts and propagated through server-side prompt aggregation. Unlike conventional prompt injection attacks, attacking TCPO targets the collaborative optimization loop in TCPO. This setting is more challenging because malicious instructions must survive aggregation, persist through ...
| Authors | Xinting Liao, Behnoosh Zamanlooy, Masoumeh Shafieinejad et al. |
|---|---|
| Primary category | cs.CR |
| Published | 21 July 2026 |
| Last updated at source | 30 July 2026 |
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