Hidden-Text Prompt Injection in User-Supplied Documents - ATR-2026-00515 (2bcb4ce9-969d-5415-bbfb-d51204325cbc)
Detects prompt injection via visually hidden text embedded in documents, resumes, or web content passed to an LLM. Attackers use white-on-white text, zero-font-size, display:none, zero-width Unicode characters, or HTML comments to hide override instructions that are invisible to human reviewers but readable by the model. OWASP LLM08:2025 Vector and Embedding Weaknesses. Patterns cover: (1) zero-width Unicode characters (U+200B, U+200C, U+200D, U+FEFF, U+2060) combined with instruction-override keywords; (2) CSS invisible text (color:white, font-size:0, opacity:0) containing override verbs; (3) HTML comment blocks with override instructions; (4) bracket-wrapped system-override blocks [[SYSTEM: ...]] in document body; (5) OVERRIDE keyword + safety-bypass + PII or exfil target.