CVE-2022-1393 in WP Subtitle Plugin
Summary
by MITRE • 05/16/2022
The WP Subtitle WordPress plugin before 3.4.1 adds a subtitle field and provides a shortcode to display it via [wp_subtitle]. The subtitle is stored as a custom post meta with the key: "wps_subtitle", which is sanitized upon post save/update, however is not sanitized when updating it directly from the post meta update button (via AJAX) - and this makes the XSS exploitable by authenticated users with a role as low as contributor.
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Analysis
by VulDB Data Team • 05/18/2022
The vulnerability identified as CVE-2022-1393 resides within the WP Subtitle WordPress plugin, a widely used tool for adding subtitle functionality to WordPress posts and pages. This particular flaw affects versions prior to 3.4.1 and represents a significant security oversight that allows for cross-site scripting attacks through improperly sanitized user input. The plugin introduces a subtitle field that can be added to posts and displayed using the shortcode [wp_subtitle], creating a legitimate functionality that becomes compromised due to inconsistent input validation mechanisms.
The technical flaw manifests in the inconsistent sanitization of the subtitle field data, specifically when it is updated through the post meta update button via AJAX requests. While the plugin properly sanitizes subtitle data when posts are saved or updated through normal WordPress workflows, it fails to apply the same sanitization measures when the subtitle is modified directly through the AJAX endpoint used by the post meta update functionality. This discrepancy creates a vector for exploitation where malicious input can bypass the security controls that would normally prevent the injection of harmful scripts.
The operational impact of this vulnerability is particularly concerning given that it requires only a low-level user role to exploit successfully. An authenticated user with contributor privileges can leverage this weakness to inject malicious JavaScript code into the subtitle field, which then gets executed when the [wp_subtitle] shortcode is rendered on the website. This creates a persistent XSS attack vector that can be used to steal session cookies, redirect users to malicious sites, or perform other malicious actions against authenticated users. The vulnerability effectively undermines the security model of WordPress by allowing users with minimal privileges to execute code with the privileges of their authenticated session.
This vulnerability maps directly to CWE-79, which defines Cross-Site Scripting as a weakness where untrusted data is embedded into web pages viewed by other users without proper validation or sanitization. The issue also aligns with ATT&CK technique T1566.001, which covers the exploitation of web applications through injection attacks. The vulnerability demonstrates a classic example of inconsistent input validation where security controls are applied selectively rather than uniformly across all data modification pathways, creating exploitable gaps in the application's security posture.
The mitigation strategy for this vulnerability requires immediate patching of the WP Subtitle plugin to version 3.4.1 or later, where the sanitization inconsistency has been addressed. Organizations should also implement additional monitoring for suspicious activity related to post meta updates, particularly when users with contributor roles attempt to modify subtitle fields. Security teams should consider implementing content security policies to further limit the impact of potential XSS attacks, and administrators should review user permissions to ensure that only trusted users have contributor-level access to prevent exploitation. Regular security audits of WordPress plugins should be conducted to identify similar inconsistencies in input validation and sanitization practices across the entire WordPress ecosystem.