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Date: Sat, 4 Jan 2020 01:05:57 -0500
From: hyp3rlinx <>
Subject: [FD] Microsoft Windows VCF Card / Mailto Link Denial Of Service

[+] 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

[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"></a>\n'

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

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

[POC Video URL]

[Network Access]


[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).


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