“Adguard is a multifunctional program for blocking ads and pop-ups, as well as protection from viruses and phishing threats. Adguard removes advertising equally well in any browser, and that is why it stands out among other adblock browser plug-ins.”

I personally use it as a Chrome browser extension. Once, Adguard classified an online shop as a malware page and prevented me from visiting it (example picture):

By clicking “Advanced” link, you are redirected to an online reputation check page:

http://adguard.com/en/adguard-report/adguard.com/report.html

But can we make a malicious site more… malicious?

Well, thanks to the lack of input validation we can. Lets check if adguard.com<img src=x onerror=alert(\”lubi.cz\”)> is harmful.

What did you expect…? It was possible to steal user’s cookies this way.

[October 15th 2014] - bug was reported
[October 16th 2014] - bug was fixed in less than 24 hours