Stored XSS in Hostel WordPress Plugin

Executive Summary

The Hostel plugin for WordPress has a Stored Cross-Site Scripting (XSS) vulnerability in the 'wphostel-book' shortcode in all versions up to and including 1.1.7.

This vulnerability arises because user-supplied shortcode attributes are not properly sanitized or escaped before being output.

Specifically, the second shortcode attribute, which is used as button text, is assigned to a variable without sanitization and then output directly into an HTML value attribute without escaping.

As a result, authenticated attackers with Contributor-level access or higher can inject arbitrary web scripts into pages, which will execute whenever a user accesses those pages.

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Detection Guidance

This vulnerability involves the 'wphostel-book' shortcode in the Hostel WordPress plugin up to version 1.1.7, where the second shortcode attribute is not properly sanitized or escaped, allowing stored cross-site scripting.

To detect this vulnerability on your system, you can search for usage of the 'wphostel-book' shortcode in your WordPress pages or posts, especially looking for suspicious or unexpected script tags or HTML attributes in the button text attribute.

You can also scan your WordPress database for posts or pages containing the shortcode with potentially malicious script injections.

• Use WP-CLI to search for the shortcode in post content: wp db query "SELECT ID, post_title FROM wp_posts WHERE post_content LIKE '%[wphostel-book%'"
• Manually inspect the shortcode attributes in the content returned for suspicious script tags or unusual HTML.
• Monitor HTTP traffic for unexpected script execution or alerts from web application firewalls related to the 'wphostel-book' shortcode.

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Impact Analysis

This vulnerability can allow attackers with Contributor-level access or above to inject malicious scripts into your website's pages.

When other users visit these pages, the injected scripts will execute in their browsers, potentially leading to theft of sensitive information, session hijacking, or other malicious actions.

Because the vulnerability is a Stored Cross-Site Scripting issue, the malicious code persists on the site and affects all visitors to the infected pages.

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Compliance Impact

The vulnerability allows authenticated attackers with Contributor-level access and above to inject arbitrary web scripts via stored cross-site scripting (XSS). This can lead to unauthorized access or manipulation of user data when users access the injected pages.

Such unauthorized script execution can compromise the confidentiality and integrity of user data, potentially violating data protection requirements under standards like GDPR and HIPAA, which mandate safeguarding personal and sensitive information against unauthorized access or disclosure.

Therefore, this vulnerability could negatively impact compliance with these regulations by exposing user data to cross-site scripting attacks.

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Mitigation Strategies

The immediate mitigation step is to update the Hostel WordPress plugin to a version later than 1.1.7 where this vulnerability is fixed.

If an update is not immediately available, restrict Contributor-level and higher user access to trusted users only, as the vulnerability requires authenticated users with Contributor-level access or above.

Additionally, consider disabling or removing the 'wphostel-book' shortcode temporarily to prevent exploitation.

Implement web application firewall (WAF) rules to detect and block attempts to inject scripts via shortcode attributes.

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