A flaw within Microsoft’s Copilot has been allowing attackers to steal the personal information of users with a single click. Called the ‘Reprompt’ exploit by the researchers at the Varonis Threat Labs, a new report from the data security research firm details the way that the vulnerability permits attackers to gain an entry point to perform a data-exfiltration chain that bypasses security controls to access data without detection.
According to the researchers, an attacker using the Reprompt exploit would send a user a phishing link. Once the link was opened, it would begin a multi-stage prompt injection process that uses a ‘q parameter.’ This would enable the attacker to request information about the victim from Copilot, such as the victim's address or the files they recently viewed. They could access this data even if Copilot was closed.
The researchers had found that "By including a specific question or instruction in the Q parameter, developers and users can automatically populate the input field when the page loads causing the AI system to execute the prompt immediately."
This means that an attacker could issue a Q parameter that asks Copilot to send data back to the attacker's server, even though Copilot is designed to specifically refuse to fetch URLs like this. Varonis researchers were able to engineer prompts to Copilot in ways that bypassed safeguards and asked the AI to fetch the URL in a way that the AI wasn't designed to.
How to stay safe from Reprompt
The good news is that the exploit has already been reported to Microsoft way back in August of 2025, and has been patched this week, so it has been fixed. That means there is currently no risk of it impacting users, particularly if you regularly update your operating system with available patches and updates.
However, it’s still recommended that users be extremely careful about what kind of information they share with their AI assistants and be on the lookout for phishing attempts. That means don't click on links that get sent to you from unexpected sources, especially ones that link to your AI assistant of choice.
Because Reprompt initiates from a phishing link, it is particularly important to follow the guidelines to protect yourself against phishing attempts. Don't open or click anything you're not expecting, especially if it uses urgency or threatening language. Hover over links to see where they redirect to. Use one of the best antivirus programs, and make sure you've enabled all the features it offers to help keep you safe online, such as browser warnings, a VPN and anti-phishing measures.
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