Security researchers at Varonis identified a significant vulnerability in Microsoft 365 Copilot for enterprise that permitted attackers to extract sensitive user data without explicit authorization. The researchers employed an unconventional discovery method, repeatedly questioning the AI assistant about its safety mechanisms until Copilot disclosed an undocumented parameter designed to prevent unauthorized command execution.
The critical parameter, identified as ?autorun=1, when combined with the well-known ?q= parameter, allowed prompts to execute automatically upon a user clicking a malicious URL. Researchers crafted links that, once clicked, instructed Copilot to search inbox contents, extract sender email addresses, retrieve stored passwords, and transmit this information to attacker-controlled servers. The exfiltrated data was converted to base64 format to mask the theft and prevent transmission errors. Users required no further action beyond clicking the link for the attack to succeed, even if they immediately closed the Copilot browser tab.
Varonis researchers also discovered a separate attack vector targeting Copilot’s permanent memory feature, which stores user preferences and instructions across sessions. By injecting malicious prompts into webpage metadata, attackers could poison this memory store to filter information, bias responses, or execute specific actions. Unlike session-based compromises, this attack persists across password changes and device re-enrollments, remaining undetectable without manual inspection.
Microsoft implemented an initial mitigation in February following Varonis’s disclosure, preventing the ?q= parameter from injecting text directly. The company deployed more comprehensive fixes later this week. Microsoft stated that customers are automatically protected and that the company continuously updates its guardrails against similar attack techniques. The incident underscores ongoing security challenges in enterprise AI systems and highlights the importance of user caution when interacting with suspicious links.
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