How ‘Reprompt’ Attack Let Hackers Steal Data From Microsoft Copilot

Varonis Threat Labs disclosed a novel attack named “Reprompt” that abused Copilot Personal’s ability to accept prefilled prompts via a URL parameter, combined with a double-request bypass and chained server-driven requests, to maintain session control and stealthily exfiltrate sensitive data; Microsoft has patched the flaw in January 2026 and enterprise Microsoft 365 Copilot was not impacted.