One Click to Compromise: Microsoft Copilot’s “Reprompt” Flaw Exposed

A new report from Varonis Threat Labs has revealed a flaw in Microsoft Copilot Personal, dubbed “Reprompt,” that could allow attackers to exfiltrate data with a single mouse click before the patch. According to Varonis Threat Labs, a click on a legitimate Microsoft link is all that’s required, with no plugins or further user interaction with Copilot. The attack is described as persistent: the attacker retains control even when the Copilot chat is closed, enabling silent data exfiltration from the victim’s session.

Researchers warn that Reprompt is designed to be undetectable by client‑side tools, since all commands are delivered from the server after the initial prompt. Microsoft has since patched the vulnerability, and users are advised to treat URL and external inputs as untrusted to help mitigate similar risks. 16 January 2026.