Adversarial Testing Catches Silent Prompt Injection Regression in Doc Assistant
OpeningBird6240 · reddit · 2026-08-09
After a prompt refactor, a document assistant began giving retrieved document text too much authority. An adversarial test document with hidden malicious instructions successfully triggered a prompt injection, causing the assistant to execute untrusted text as commands.
The team caught this silent regression using existing adversarial evals in their release pipeline (via Braintrust). By examining the trace, they pinpointed exactly where the agent started treating retrieved text like system instructions.
The fix involved rewriting the prompt hierarchy and adding a stricter scorer to prevent retrieved data from overriding system instructions. The key takeaway is the necessity of maintaining a strict hierarchy of trust between system prompts and retrieved data.
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