cyb3rmik3/prompt-injection-email-samples, michalos.net（@Cyb3rMik3）cyb3rmik3/prompt-injection-email-samples · 2 sources · 2 reports · Hands-on test of Microsoft Defender email prompt injection blocking
Researchers released an open-source email prompt injection test set for testing whether email security gateways and AI email assistants can identify indirect prompt injection instructions in emails. The test set is designed with Microsoft Defender for Office 365's prompt injection protection in mind; samples are standard .eml emails and can also be used with other secure email gateways, Copilot, Gemini, and custom RAG pipelines. It covers three intent categories—system prompt leakage, data exfiltration via URLs, and probing of tools and write permissions—and four delivery encodings: plaintext visible, hidden HTML, Base64, and zero-width characters. Testers tested the new email prompt injection protection in Defender for Office 365 Plan 2 and found that emails with Base64 and zero-width character encoding bypassed mail flow filtering, but Copilot decoded and refused to answer at runtime; delivery does not equal compromise. The protection focuses on three intent categories: data exfiltration, extracting system prompts, and probing tools and write permissions. High-confidence emails are directly quarantined and classified as High Confidence Phish, with the new Detection Technology value set to Prompt Injection.