LLM Refund Agent Hacked via Prompt Injection
jokiruiz · reddit · 2026-07-14
After being hit by a prompt injection, an LLM refund agent erroneously approved a 4000€ refund for an order that was only 1299€.
The author concludes that the solution isn't to "write stricter prompts," but rather to use code for hard validation after model output, treating the LLM as untrusted input. Examples include:
- order[
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