Why This Matters
As someone who’s spent years juggling Exchange servers, Office 365 policies, and the occasional “oops” moment in Hyper-V, I’ve learned that the scariest attacks are the ones that look deceptively simple. The newly disclosed Reprompt attack is exactly that: one click on a malicious link, and suddenly your Copilot session isn’t yours anymore.
How Reprompt Worked
Researchers at Varonis discovered that attackers could:
- Inject prompts via the
qparameter in a URL — Copilot would execute them automatically when the page loaded. - Bypass guardrails using a “double-request” trick — the first request gets blocked, but the second slips through.
- Chain requests from an attacker’s server — allowing continuous, invisible data exfiltration.
I’ve seen similar “parameter injection” issues back in the day with poorly secured web apps. Back in 2019, I tested a custom portal on Server 2016 and a single malformed query string bricked the VM. This one felt eerily familiar.
My Take as a Tech Admin
Not gonna lie, the idea that Copilot could be hijacked with just a crafted URL gave me flashbacks. I’ve tested Copilot Personal in beta on my ThinkPad running Hyper-V with 32GB RAM, and I remember thinking: “This thing is powerful, but it’s also sitting right in the middle of my workflow.” That’s both a blessing and a risk.
Most guides will tell you phishing is the main vector, but here’s the contradiction: the exploit didn’t need plugins or shady extensions—just a click. That’s what makes it dangerous. The install screen doesn’t scream “you’re compromised”; it just sits there, black and silent, while your data walks out the back door.
What’s Fixed
- Microsoft patched the issue on January 14, 2026.
- Exploitation hasn’t been seen in the wild.
- The attack only impacted Copilot Personal, not Microsoft 365 Copilot, which has stronger enterprise protections like Purview auditing and tenant-level DLP.
Lessons Learned
- Patch immediately — don’t wait for the weekend.
- Educate users — one click is all it takes.
- Segregate environments — I’ve started keeping my test Copilot sessions separate from production accounts. It’s like running DNS on a rainy Tuesday in Bengaluru: you don’t want your main box bricked because you were winging it.
Final Thoughts
This attack is a reminder that even shiny new AI assistants are still software, and software can be exploited. Ever spent an hour debugging a typo? Welcome to my world. Now imagine debugging invisible exfiltration from your Copilot session.
