CVE-2025-9565 in Blocksy Companion Plugin
Summary
by MITRE • 09/17/2025
The Blocksy Companion plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the plugin's blocksy_newsletter_subscribe shortcode in all versions up to, and including, 2.1.10 due to insufficient input sanitization and output escaping on user supplied attributes. This makes it possible for authenticated attackers, with contributor-level access and above, 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 • 09/17/2025
The Blocksy Companion plugin for WordPress presents a critical stored cross-site scripting vulnerability identified as CVE-2025-9565 affecting versions through 2.1.10. This vulnerability stems from inadequate input sanitization and output escaping mechanisms within the plugin's blocksy_newsletter_subscribe shortcode implementation. The flaw allows authenticated attackers possessing contributor-level privileges or higher to inject malicious JavaScript code into the plugin's shortcode attributes. When victims access pages containing the compromised shortcode, the injected scripts execute in their browsers, creating a persistent threat vector that can affect any user who views the affected content.
The technical exploitation of this vulnerability occurs through the manipulation of shortcode attributes that are not properly sanitized before being rendered in web pages. Attackers can leverage this weakness by crafting malicious payloads within the newsletter subscription shortcode parameters, which are then stored within the WordPress database. When other users access pages containing these compromised shortcodes, their browsers execute the injected scripts without proper validation or escaping. This stored XSS vulnerability operates at the application layer and can be particularly dangerous because the malicious code persists in the database and executes automatically whenever the affected content is loaded, making it difficult to contain and remediate.
The operational impact of this vulnerability extends beyond simple script execution as it enables attackers to perform various malicious activities including session hijacking, credential theft, data exfiltration, and redirection to malicious sites. Contributors and higher privilege users can manipulate the plugin's functionality to inject persistent malicious code, potentially compromising the entire WordPress installation. The vulnerability affects the core integrity of the content management system by allowing unauthorized code execution within the context of authenticated users' browsers. This threat is particularly concerning for websites that rely on contributor-level access for content management, as these users often have significant influence over published content and can introduce persistent threats that affect all site visitors.
Security professionals should implement immediate mitigations including updating to the latest plugin version that addresses this vulnerability, implementing proper input validation and output escaping mechanisms, and conducting thorough security audits of all plugin installations. The vulnerability aligns with CWE-79 which specifically addresses cross-site scripting flaws, and can be mapped to ATT&CK technique T1566.001 for credential access through social engineering. Organizations should also consider implementing web application firewalls, monitoring for suspicious shortcode modifications, and establishing strict access controls for contributor accounts. Regular security scanning of WordPress installations for vulnerable plugins remains essential to prevent exploitation of similar stored XSS vulnerabilities that could compromise user sessions and sensitive data.