CVE-2023-4283 in EmbedPress Plugin
Summary
by MITRE • 08/10/2023
The EmbedPress plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'embedpress_calendar' shortcode in versions up to, and including, 3.8.2 due to insufficient input sanitization and output escaping on user supplied attributes. This makes it possible for authenticated attackers with contributor-level and above permissions to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.
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Analysis
by VulDB Data Team • 09/05/2023
The EmbedPress plugin for WordPress represents a widely used tool for embedding various media content including calendars, videos, and documents directly into WordPress sites. This vulnerability affects versions up to and including 3.8.2, where the plugin fails to properly sanitize user input when processing the 'embedpress_calendar' shortcode. The flaw stems from inadequate validation and escaping mechanisms that allow malicious actors to inject malicious code through shortcode attributes. The vulnerability specifically targets the calendar shortcode functionality which processes user-supplied parameters without sufficient sanitization, creating a persistent XSS vector that can be exploited by authenticated users with contributor-level permissions or higher.
The technical exploitation of this vulnerability occurs through the manipulation of shortcode attributes that are processed by the plugin's backend code. When an attacker with appropriate privileges creates or modifies a post containing the vulnerable shortcode with malicious parameters, the injected scripts become permanently stored within the WordPress database. This stored nature of the vulnerability means that any user who accesses a page containing the compromised shortcode will execute the malicious code within their browser context. The vulnerability is classified as a stored XSS attack under CWE-79 which specifically addresses improper neutralization of input during web page generation. The issue manifests when user-supplied attributes are directly embedded into HTML output without proper escaping, creating opportunities for attackers to execute arbitrary JavaScript code in victims' browsers.
From an operational impact perspective, this vulnerability presents significant risks to WordPress sites utilizing the EmbedPress plugin. Attackers can leverage this weakness to perform session hijacking, steal administrator credentials, inject malicious advertisements, or redirect users to phishing sites. The requirement for contributor-level access or higher means that the vulnerability can be exploited by users who have legitimate access to content creation features, making it particularly dangerous in environments where multiple users have elevated permissions. The persistent nature of stored XSS means that the malicious code will continue to execute for all users who view affected pages until the vulnerability is patched and the malicious content is removed from the database. This vulnerability aligns with ATT&CK technique T1566.001 which covers credential access through social engineering and malicious content delivery.
Mitigation strategies for this vulnerability should focus on immediate patching of the EmbedPress plugin to version 3.8.3 or later where the sanitization issues have been addressed. Administrators should also implement strict content review processes and monitor for unauthorized shortcode usage within their WordPress installations. Network-level protections such as web application firewalls can help detect and block known malicious patterns, though these should not be relied upon as the sole defense mechanism. Regular security audits of WordPress plugins and themes should be conducted to identify similar sanitization issues in other components. Additionally, implementing proper user permission controls and limiting contributor-level access to only essential functionality can reduce the attack surface. The vulnerability demonstrates the critical importance of input validation and output escaping in web applications, reinforcing the need for developers to follow secure coding practices as outlined in OWASP Top Ten and other industry security standards.