Threat
Imprompter: Tricking LLM Agents into Improper Tool Use
Publication date not yet evaluated · Added arxiv.org
Page published
Coverage timeline
Single-source incident — one report is available.
Why it matters
The Le Chat fix shows that obfuscated adversarial prompts can automatically drive production LLM agents to exfiltrate user PII via markdown rendering, a data-exfiltration class defenders must guard against across chat assistants.
Mistral patched an obfuscated prompt-injection flaw in its Le Chat assistant on September 13, 2026 that could coax the model into extracting a user's personally identifiable information and formatting it into a markdown command that leaks the data to an attacker's server. The technique stems from the 'Imprompter' research by Xiaohan Fu and Earlence Fernandes (arXiv:2410.14923), which demonstrated automatically computed adversarial prompts against production agents including Le Chat, ChatGLM, and Llama with roughly 80% success; Mistral states the attack required victims to paste adversarial text and supply their own data, and that no users were impacted.