phpMyAdmin 3.x Multiple Remote Code Executions

This post details a few interesting vulnerabilities I found while relaxing and reading the sourcecode of phpMyAdmin. My original advisory can be found here.

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The first vulnerability
File: libraries/auth/swekey/swekey.auth.lib.php
Lines: 266-276
Patched in: 3.3.10.2 and 3.4.3.1
Type: Variable Manipulation
Assigned CVE id: CVE-2011-2505
PMA Announcement-ID: PMASA-2011-5

266  if (strstr($_SERVER['QUERY_STRING'],'session_to_unset') != false)
267  {
268      parse_str($_SERVER['QUERY_STRING']);
269      session_write_close();
270      session_id($session_to_unset);
271      session_start();
272      $_SESSION = array();
273      session_write_close();
274      session_destroy();
275      exit;
276  }

Notice the call to parse_str on line 268 that passes the query string as it's first argument. It's missing a second argument. This means that what ever parameters and values are present in the query string will be used as variables in the current namespace. But since the code path that executes the call to parse_str inevitably leads to a call to exit there ain't much to exploit. However the session variables persists between requests. Thus giving us full control of the $_SESSION array.

From here on there are numerous XSS and SQL injection vulnerabilities open for attack. But we'll focus on three far more serious vulnerabilities.


The second vulnerability
Patched in: 3.3.10.2 and 3.4.3.1
Type: Remote Static Code Injection
Assigned CVE id: CVE-2011-2506
PMA Announcement-ID: PMASA-2011-6

File: setup/lib/ConfigGenerator.class.php
Lines: 16-78
16  /**
17   * Creates config file
18   *
19   * @return string
20   */
21  public static function getConfigFile()
22  {
23      $cf = ConfigFile::getInstance();
24   
25      $crlf = (isset($_SESSION['eol']) && $_SESSION['eol'] == 'win') ? "\r\n" : "\n";
26      $c = $cf->getConfig();
27   
28      // header
29      $ret = '<!--?php' . $crlf
30          . '/*' . $crlf
31          . ' * Generated configuration file' . $crlf
32          . ' * Generated by: phpMyAdmin '
33                  . $GLOBALS['PMA_Config']--->get('PMA_VERSION')
34                  . ' setup script' . $crlf
35          . ' * Date: ' . date(DATE_RFC1123) . $crlf
36          . ' */' . $crlf . $crlf;
37   
38      // servers
39      if ($cf->getServerCount() > 0) {
40          $ret .= "/* Servers configuration */$crlf\$i = 0;" . $crlf . $crlf;
41          foreach ($c['Servers'] as $id => $server) {
42              $ret .= '/* Server: ' . strtr($cf->getServerName($id), '*/', '-') . " [$id] */" . $crlf
43                  . '$i++;' . $crlf;
44              foreach ($server as $k => $v) {
45                  $k = preg_replace('/[^A-Za-z0-9_]/', '_', $k);
46                  $ret .= "\$cfg['Servers'][\$i]['$k'] = "
47                      . (is_array($v) && self::_isZeroBasedArray($v)
48                              ? self::_exportZeroBasedArray($v, $crlf)
49                              : var_export($v, true))
50                      . ';' . $crlf;
51              }
52              $ret .= $crlf;
53          }
54          $ret .= '/* End of servers configuration */' . $crlf . $crlf;
55      }
56      unset($c['Servers']);
57   
58      // other settings
59      $persistKeys = $cf->getPersistKeysMap();
60   
61      foreach ($c as $k => $v) {
62          $k = preg_replace('/[^A-Za-z0-9_]/', '_', $k);
63          $ret .= self::_getVarExport($k, $v, $crlf);
64          if (isset($persistKeys[$k])) {
65              unset($persistKeys[$k]);
66          }
67      }
68      // keep 1d array keys which are present in $persist_keys (config.values.php)
69      foreach (array_keys($persistKeys) as $k) {
70          if (strpos($k, '/') === false) {
71              $k = preg_replace('/[^A-Za-z0-9_]/', '_', $k);
72              $ret .= self::_getVarExport($k, $cf->getDefault($k), $crlf);
73          }
74      }
75      $ret .= '?>';
76   
77      return $ret;
78  }

On line 42 in this file a comment is created to show some additional information in a config file. We can see that the output of the call to $cf->getServerName($id) is sanitized to prevent user input from closing the comment. However $id, the key of the $c['Servers'] array, is not. So if we could rename a key in this array we could close the comment and inject arbitrary PHP code.
On line 26 the $c array is created from a call to $cf->getConfig().

File: libraries/config/ConfigFile.class.php
Lines: 469-482
469  /**
470   * Returns configuration array (full, multidimensional format)
471   *
472   * @return array
473   */
474  public function getConfig()
475  {
476      $c = $_SESSION[$this->id];
477      foreach ($this->cfgUpdateReadMapping as $map_to => $map_from) {
478          PMA_array_write($map_to, $c, PMA_array_read($map_from, $c));
479          PMA_array_remove($map_from, $c);
480      }
481      return $c;
482  }

Bingo! The $c array is derived from the $_SESSION array hence we could have full control of its contents by utilizing the first vulnerability. Now we can inject arbitrary PHP code that will be saved into the file config/config.inc.php. Then we would just browse to this file and the webserver would executed it.

This vulnerability requires one specific condition. The config directory must have been left in place after the initial configuration. This is something advised against and hence a majority of servers wont be susceptible to this attack. Therefor we'll check out a third and a fourth vulnerability.


The third vulnerability
Patched in: 3.3.10.2 and 3.4.3.1
Type: Authenticated Remote Code Execution
Assigned CVE id: CVE-2011-2507
PMA Announcement-ID: PMASA-2011-7

File: server_synchronize.php
Line: 466
466  $trg_db = $_SESSION['trg_db'];
Line: 477
477  $uncommon_tables = $_SESSION['uncommon_tables'];
Line: 674
674  PMA_createTargetTables($src_db, $trg_db, $src_link, $trg_link, $uncommon_tables, $uncommon_table_structure_diff[$s], $uncommon_tables_fields, false);
File: libraries/server_synchronize.lib.php
Lines: 613-631
613  function PMA_createTargetTables($src_db, $trg_db, $src_link, $trg_link, &$uncommon_tables, $table_index, &$uncommon_tables_fields, $display)
614  {
615      if (isset($uncommon_tables[$table_index])) {
616          $fields_result = PMA_DBI_get_fields($src_db, $uncommon_tables[$table_index], $src_link);
617          $fields = array();
618          foreach ($fields_result as $each_field) {
619              $field_name = $each_field['Field'];
620              $fields[] = $field_name;
621          }
622          $uncommon_tables_fields[$table_index] = $fields;
623          
624          $Create_Query = PMA_DBI_fetch_value("SHOW CREATE TABLE " . PMA_backquote($src_db) . '.' . PMA_backquote($uncommon_tables[$table_index]), 0, 1, $src_link);
625   
626          // Replace the src table name with a `dbname`.`tablename`
627          $Create_Table_Query = preg_replace('/' . PMA_backquote($uncommon_tables[$table_index]) . '/',
628                                              PMA_backquote($trg_db) . '.' .PMA_backquote($uncommon_tables[$table_index]),
629                                              $Create_Query,
630                                              $limit = 1
631          );

The variables $uncommon_tables[$table_index] and $trg_db are derived from the $_SESSION array. By utilizing the first vulnerability we can inject what ever we want into both the first and the second argument of the function preg_replace on lines 627-631. In a previous post to this blog I've detailed how this condition can be turned into a remote code execution. Basicly we can inject the "e" modifier into the regexp pattern which causes the second argument to be executed as PHP code.

This vulnerability have two major restrictions from an attackers perspective. First the Suhosin patch that completly defends against this type of attack. Second, this piece of code can only be reached if we're authenticated. So to exploit it we would need to have previous knowledge of credentials to an account of the database that phpMyAdmin is set up to manage. Except for some obscure configurations that allows us to bypass this restriction.

Since the Suhosin patch is pretty popular, and for example compiled by default in OpenBSD's PHP packages, it's worth exploring a fourth vulnerability.


The fourth vulnerability
Patched in: 3.3.10.2 and 3.4.3.1
Type: Path Traversal
Assigned CVE id: CVE-2011-2508
PMA Announcement-ID: PMASA-2011-8

File: libraries/display_tbl.lib.php
Lines: 1291-1299
1291  if ($GLOBALS['cfgRelation']['mimework'] && $GLOBALS['cfg']['BrowseMIME']) {
1292   
1293      if (isset($GLOBALS['mime_map'][$meta->name]['mimetype']) && isset($GLOBALS['mime_map'][$meta->name]['transformation']) && !empty($GLOBALS['mime_map'][$meta->name]['transformation'])) {
1294          $include_file = $GLOBALS['mime_map'][$meta->name]['transformation'];
1295   
1296          if (file_exists('./libraries/transformations/' . $include_file)) {
1297              $transformfunction_name = str_replace('.inc.php', '', $GLOBALS['mime_map'][$meta->name]['transformation']);
1298   
1299              require_once './libraries/transformations/' . $include_file;


This fourth vulnerability is a directory traversal in a call to require_once which can be exploited as a local file inclusion. The variable $GLOBALS['mime_map'][$meta->name]['transformation'] is derived from user input. For example, by setting $GLOBALS['mime_map'][$meta->name]['transformation'] to "../../../../../../etc/passwd" the local passwd-file could show up.

This vulnerability can only be reached if we're authenticated and requires that the transformation feature is setup correctly in phpMyAdmin's configuration storage. However, the $GLOBALS['cfgRelation'] array is derived from the $_SESSION array. Hence the variable $GLOBALS['cfgRelation']['mimework'] used to check this can be modified using the first vulnerability.

File: libraries/display_tbl.lib.php
Lines: 707-710
707  if ($GLOBALS['cfgRelation']['commwork'] && $GLOBALS['cfgRelation']['mimework'] && $GLOBALS['cfg']['BrowseMIME'] && ! $_SESSION['tmp_user_values']['hide_transformation']) {
708      require_once './libraries/transformations.lib.php';
709      $GLOBALS['mime_map'] = PMA_getMIME($db, $table);
710  }
And the fact that $GLOBALS['mime_map'] is conditionally initialized together with the fact that phpMyAdmin registers all request variables in the global namespace (blacklists some, but not mime_map) allows us to set $GLOBALS['mime_map'][$meta->name]['transformation'] to whatever we want, even when the transformation feature is not setup correctly.


Summary

    If the config folder is left in place, phpMyAdmin is vulnerable.

    If an attacker has access to database credentials and the Suhosin patch is not installed, phpMyAdmin is vulnerable.

    If an attacker has access to database credentials and knows how to exploit a local file inclution, phpMyAdmin is vulnerable.