EchoLeak: a zero-click email silently exfiltrated data from Microsoft 365 Copilot (CVE-2025-32711, CVSS 9.3)

EchoLeak (CVE-2025-32711, CVSS 9.3) was the first documented zero-click prompt-injection exploit against a production LLM system — Microsoft 365 Copilot across Word, Excel, PowerPoint, Outlook, and Teams. An attacker sent a benign-looking email containing a hidden prompt (an HTML comment or white-on-white text). The payload was invisible to the user but parsed and retained by Copilot's engine. Later, when the user asked Copilot something ordinary like 'summarize recent strategy updates,' the retrieval-augmented-generation engine pulled the malicious email into context and executed its instructions — exfiltrating internal documents, emails, and files through markdown links and images, bypassing Microsoft's prompt-injection classifiers, link redaction, and CSP. Discovered by Aim Security and disclosed in June 2025, it required zero clicks from the victim and exposed how RAG-based AI assistants inherit the trust of everything they can read.