[FD] SQLi in Relevanssi might allow an admin to read contents of database (WordPress plugin)

[dxw Security <harry@xxxxxxx>]

Details
================
Software: Relevanssi
Version: 3.5.12,3.6.0
Homepage: https://wordpress.org/plugins/relevanssi/
Advisory report: https://advisories.dxw.com/advisories/sqli-relevanssi/
CVE: Awaiting assignment
CVSS: 8.5 (High; AV:N/AC:L/Au:S/C:C/I:C/A:N)

Description
================
SQLi in Relevanssi might allow an admin to read contents of database

Vulnerability
================
If logged in as an administrator on any site, you can go to Settings > 
Relevanssi Premium and potentially extract all values in the database including 
password hashes and user activation tokens.
This is achieved by a SQL injection based on the fact that some of the 
configuration options are appended into a SQL query in a unsafe way.
The configuration page contains the following code, that allows the user to set 
the option relevanssi_post_type_weights to any value:
function update_relevanssi_options() {
    ....
    foreach ($_REQUEST as $key => $value) {
        if (substr($key, 0, strlen(\'relevanssi_weight_\')) == 
\'relevanssi_weight_\') {
            $type = substr($key, strlen(\'relevanssi_weight_\'));
            $post_type_weights[$type] = $value;
        }
        ....
    }
    if (count($post_type_weights) > 0) {
        update_option(\'relevanssi_post_type_weights\', $post_type_weights);
    }
    ....
}
Now when a search is made, the function relevanssi_search is called, this 
appends the user controled value into the SQL query:
$post_type_weights = get_option(\'relevanssi_post_type_weights\');

...

!empty($post_type_weights[\'post_tag\']) ? $tag = 
$post_type_weights[\'post_tag\'] : $tag = 
$relevanssi_variables[\'post_type_weight_defaults\'][\'post_tag\'];

!empty($post_type_weights[\'category\']) ? $cat = 
$post_type_weights[\'category\'] : $cat = 
$relevanssi_variables[\'post_type_weight_defaults\'][\'category\'];

$query = \"SELECT relevanssi.*, relevanssi.title * $title_boost +
          relevanssi.content + relevanssi.comment * $comment_boost +
          relevanssi.tag * $tag + relevanssi.link * $link_boost +
          relevanssi.author + relevanssi.category * $cat + relevanssi.excerpt +
          relevanssi.taxonomy + relevanssi.customfield + relevanssi.mysqlcolumn 
AS tf
          FROM $relevanssi_table AS relevanssi $query_join
          WHERE $term_cond $query_restrictions\";

Proof of concept
================

Visit /wp-admin/options-general.php?page=relevanssi%2Frelevanssi.php
Assign 0.75\' (the default value plus a single quote at the end) to “Tag weight”
Press “Save the options”
Visit /?s=test
The logs should contain the following error because of the syntax error we 
introduced: “WordPress database error You have an error in your SQL syntax”

Note: while it’s possible to inject syntax errors, it’s currently unknown 
whether this bug can be used to inject anything that would be useful to an 
attacker.

Mitigations
================
Upgrade to version 3.6.1 or later.

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

Please contact us on security@xxxxxxx to acknowledge this report if you 
received it via a third party (for example, plugins@xxxxxxxxxxxxx) 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
2017-10-02: Reported to vendor via email
2017-10-03: First response from vendor
2017-10-03: Version 3.6.1 released which contains a fix for this bug



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


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