CVE-2026-18400 in The Slider, Gallery, and Carousel by MetaSlider Plugin
Summary
by MITRE • 08/06/2026
The Slider, Gallery, and Carousel by MetaSlider – Image Slider, Video Slider plugin for WordPress is vulnerable to Stored Cross-Site Scripting via 'delay' Post Meta Setting in all versions up to, and including, 3.111.0 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with custom-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. The ml-slider custom post type is registered without custom capability restrictions and the ml-slider_settings meta key is unprotected, allowing Author-level users to set the malicious delay value via XML-RPC custom_fields when creating an ml-slider post.
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Analysis
by VulDB Data Team • 08/06/2026
The vulnerability in the Slider Gallery and Carousel by MetaSlider plugin represents a critical stored cross-site scripting weakness that affects WordPress installations running versions up to and including 31110. This security flaw stems from inadequate input sanitization and output escaping mechanisms within the plugin's handling of the 'delay' post meta setting. The vulnerability specifically targets the ml-slider custom post type which lacks proper capability restrictions, creating an exploitable entry point for authenticated attackers who possess at least author-level privileges. The technical implementation fails to properly validate or sanitize user-supplied input before storing it in the database, allowing malicious scripts to be persisted and executed whenever affected pages are accessed by unsuspecting users.
The operational impact of this vulnerability extends beyond simple script execution as it enables attackers to establish persistent malicious presence within WordPress installations through the ml-slider custom post type. The absence of proper capability checks for the ml-slider custom post type means that users with author-level permissions can manipulate the plugin's functionality through XML-RPC interface by setting malicious values in the custom_fields parameter during ml-slider post creation. This allows attackers to inject arbitrary web scripts that will execute in the context of any user who accesses pages containing the injected content, potentially leading to session hijacking, credential theft, or further exploitation of the compromised WordPress environment. The vulnerability's persistence is particularly concerning as stored XSS attacks can affect multiple users over extended periods without requiring repeated exploitation attempts.
Security researchers should note this vulnerability aligns with CWE-79 - Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') and follows ATT&CK technique T1566.001 - Phishing via Social Media where malicious scripts can be used to redirect users or harvest credentials. The root cause lies in the plugin's failure to implement proper input validation for the delay parameter, combined with insufficient output escaping when rendering stored values back to web pages. Attackers exploiting this vulnerability can leverage XML-RPC capabilities to inject malicious code without requiring direct access to the WordPress admin interface, making detection more challenging. The vulnerability's impact is amplified by the fact that the ml-slider_settings meta key remains unprotected, allowing unauthorized modification of critical plugin parameters through legitimate XML-RPC interfaces.
Mitigation strategies should prioritize immediate plugin updates to versions that address the stored XSS vulnerability, as well as implementing proper capability restrictions for the ml-slider custom post type. Administrators should review and restrict XML-RPC access to trusted sources only, while also monitoring for suspicious activity in ml-slider posts and related meta fields. The implementation of Content Security Policy headers can provide additional defense-in-depth measures against script execution, though this approach alone does not prevent the initial injection of malicious content. Regular security audits of WordPress plugins should include verification of input sanitization practices and output escaping mechanisms to prevent similar vulnerabilities from persisting in other components of the WordPress ecosystem. Organizations should also consider implementing web application firewalls that can detect and block suspicious XML-RPC requests containing potentially malicious script content.