Missing Authorization Vulnerability in Blog2Social Plugin

On October 5, 2022, the Wordfence Threat Intelligence team responsibly disclosed a Missing Authorization vulnerability in Blog2Social, a WordPress plugin installed on over 70,000 sites that allows users to set up post sharing to various social networks. Vulnerable versions of the plugin make it possible for authenticated attackers with minimal permissions, such as subscribers, to change the plugin’s settings.

We initially reached out to the developer via email on October 1, 2022. After receiving a response from the developer shortly thereafter, we disclosed this vulnerability to their team on October 5, 2022. A partial fix was provided within a day (version 6.9.11) with a full fix following on October 10, 2022 (version 6.9.12).

At the time of discovery, we did not release a firewall rule as we determined that the vulnerability is unlikely to be targeted and has a relatively low impact. After further evaluation, we decided to release a firewall rule on October 27, 2022 as a precautionary measure. Premium, Care, and Response customers received that protection the same day, while sites still running the free version of Wordfence will receive the same protection 30 days later on November 26, 2022. As such, we strongly recommend updating to version 6.9.12 or higher of Blog2Social to ensure that your site is protected against any exploits targeting this vulnerability.

Blog2Social: Social Media Auto Post & Scheduler is a plugin offered by Blog2Social/Adenion that provides content-creators with the ability to quickly share site content to their social media accounts. It offers automatic post sharing as well as optimized scheduling and also extends some of its features to subscribers, enabling them to share posts to their own social media accounts.

As part of the plugin’s functionality, there are some more advanced settings that can be managed. Unfortunately, this was implemented insecurely making it possible for authenticated attackers to update these settings even without the authorization to do so.

More specifically, the plugin provides administrators with the ability to enable legacy mode, which is intended to reduce server load. In legacy mode, the plugin will load content one item at a time instead of loading all content in bulk in an attempt to reduce the likelihood of dashboard freeze-ups. In order to reduce the number of concurrent outgoing connections, legacy mode will also load connections to social media accounts in sequential order as opposed to doing so simultaneously. While functionality should not be significantly affected by this for most use cases, this legacy option setting is reserved for administrators only. Unfortunately, due to a lack of capability checking on the function and in the user interface, site subscribers had access to this setting via the dashboard:

/wp-admin/admin.php?page=blog2social-settings

Furthermore, the same URL offers access to a Social Meta Data tab, which contains forms that are disabled for non-administrative users. However, browsers offer inspector tools, which can be used to modify html on the fly in order to change properties of such forms and their elements. For instance, a save button with the following properties can be modified to become functional by removing the disabled attribute from the button: <button class="btn btn-primary pull-right" disabled="disabled" type="submit">save</button> – as a result, such a form can be submitted by a subscriber. This indicates the developer used client-side validation, which can easily be bypassed by modifying the request sent to the server.

A request could be submitted using a third party tool similar to this one:

POST /wp-admin/admin-ajax.php HTTP/1.1
Host: 127.0.0.1
Cookie:

b2s_og_default_title=SiteTitle&b2s_og_default_desc=Just%20another%20WordPress%20site&b2s_og_default_image=&b2s_og_imagedata_active=1&b2s_og_objecttype_active=1&b2s_og_locale_active=1&b2s_og_locale=en_US&b2s_card_default_type=Summary&b2s_card_default_title=SiteTitle&b2s_card_default_desc=Just%20another%20WordPress%20site&b2s_card_default_image=&is_admin=1&version=0&action=b2s_save_social_meta_tags&b2s_security_nonce=<nonce>

This had consequences such as allowing subscribers to change social meta tags which could potentially be used to impact brand reputation.

A third issue that we discovered surrounded the plugin’s general authorization mechanism as seen below:

public function lockAutoPostImport() {
if (current_user_can('read') && isset($_POST['b2s_security_nonce']) && (int) wp_verify_nonce(sanitize_text_field(wp_unslash($_POST['b2s_security_nonce'])), 'b2s_security_nonce') > 0) {
if (isset($_POST['userId']) && (int) $_POST['userId'] > 0) {
update_option('B2S_LOCK_AUTO_POST_IMPORT_' . (int) $_POST['userId'], 1, false);
}
echo json_encode(array('result' => true));
wp_die();
} else {
echo json_encode(array('result' => false, 'error' => 'nonce'));
wp_die();
}
}

The first if-statement is intended to prevent unauthorized use of this function and similar functions using the same protection. The following parts need to evaluate to true in order for the if-statement to do the same:

• current_user_can('read') – This gives access to the administration screens and user profiles. This permission is generally available to all authenticated users such as subscribers.
• isset($_POST['b2s_security_nonce']) – this nonce is set by the plugin and can be obtained by searching the code of /wp-admin/profile.php for the string ‘b2s_security_nonce’. This nonce is generated for subscribers and higher.
• (int) wp_verify_nonce(sanitize_text_field(wp_unslash($_POST['b2s_security_nonce'])), 'b2s_security_nonce') > 0 – this verifies the nonce after some sanitization.

As long as a userId is provided, we are able to lock B2S_LOCK_AUTO_POST_IMPORT_ for any user, resulting in that user being unable to automatically import posts. We found that many other functions lacked proper capability checks as well.

The Importance of Capability Checks

Capability checks are an important part of securing AJAX actions since those are available to any logged in users, including subscribers. The following is an example of an AJAX action from the Blog2Social plugin.

add_action('wp_ajax_b2s_lock_auto_post_import', array($this, 'lockAutoPostImport'));

While nonce checks ensure that the user initiating the request intended to do so, they don’t provide authorization. As mentioned above, the check current_user_can('read') does ensure that the user initiating the request has that specific capability, but it does not suffice to protect actions intended for administrators only. A proper way to secure such actions would be to utilize a check such as
current_user_can('manage_options').

The plugin does make use of B2S_PLUGIN_BLOG_USER_ID, which determines the current user’s ID in order to ensure that options saved are personalized thus preventing overwriting other users’ preferences:

define('B2S_PLUGIN_BLOG_USER_ID', get_current_user_id());

Timeline

October 1, 2022 – Initial outreach to the plugin developer.
October 5, 2022 – We disclosed details of the vulnerabilities with the developer.
October 6, 2022 – Version 6.9.11 is released which provides a patch for the legacy mode update vulnerability.
October 10, 2022 – The remaining authorization vulnerabilities are patched in version 6.9.12.
October 27, 2022 – Wordfence Premium, Care, and Response customers receive a firewall rule to provide additional protection.
November 26, 2022 – Wordfence Free users receive a firewall rule.

Conclusion

In today’s post, we covered several vulnerabilities in the Blog2Social: Social Media Auto Post & Scheduler plugin that could be used by subscribers to update plugin settings due to improper authorization checks. The vulnerabilities were patched by ensuring that capabilities were checked.

Wordfence Premium, Care, and Response users received a firewall rule on October 27th, 2022 for enhanced protection. Wordfence free users will receive this rule after 30 days on November 26th, 2022. We strongly recommend updating to version 6.9.12 or higher of Blog2Social: Social Media Auto Post & Scheduler to ensure that your site is protected against any exploits targeting this vulnerability.

If you believe your site has been compromised as a result of this vulnerability or any other vulnerability, we offer Incident Response services via Wordfence Care. If you need your site cleaned immediately, Wordfence Response offers the same service with 24/7/365 availability and a 1-hour response time. Both of these products include hands-on support in case you need further assistance. If you have any friends or colleagues who are using this plugin, please share this announcement with them and encourage them to update to the latest patched version of Blog2Social as soon as possible.