Vulnerability Type: XSS (Cross Site Scripting) / CWE-79

 Recently, searching the net I found a vulnerability on the site sin0nime.com.
It is a Cross Site Scripting (XSS) vulnerability. 

Visiting the original site is no danger, the site is safe and does not contain any malicious code. The problem occurs when a user sends a link, which he has previously modified, to another user. What can happen to you? A window may open with a message, you may be redirected to another site, etc.

 

 Obviously I was curious to see what the vulnerability was, and I did the research on openbugbounty.org. He was the same guy who reported another vulnerability a few months ago.

Continuing the research, I also found out the code that was used to discover the vulnerability. 

Here is the code used:

/dex/index.php?m=0">ScanT3r<svg/onload=confirm(/ScanT3r/)>web"&cheie=Stringent

 Another example of malicious script:

cheie="></title></script><svg/onload=alert(1)>&m="></title></script><svg/onload=alert(1)>

 In fact, here is a screenshot with some tentative:

The solution is simple, the input data must be verified and validated and modified if necessary. Another solution is to use a class designed specifically for this, e.g. HTML Purifier.

Example,
 

m = 0 "> ScanT3r <svg / onload = confirm (/ ScanT3r /)> web" 

will become
 

m = 0