CVE-2026-57755 Overview
CVE-2026-57755 is a stored Cross-Site Scripting (XSS) vulnerability in the Mosaic Gallery – Advanced Gallery plugin for WordPress. The flaw affects all plugin versions up to and including 1.2.0. Authenticated users with Contributor-level privileges can inject arbitrary JavaScript that executes in the browsers of other users viewing the affected content. The issue is tracked under CWE-79: Improper Neutralization of Input During Web Page Generation. Patchstack published the advisory referenced by the National Vulnerability Database.
Critical Impact
Authenticated Contributor accounts can inject persistent scripts that execute against administrators and site visitors, enabling session theft, defacement, and further account compromise.
Affected Products
- Mosaic Gallery – Advanced Gallery WordPress plugin versions <= 1.2.0
- WordPress sites permitting Contributor-level content submission with the plugin enabled
- Multisite WordPress installations where the plugin is network-activated
Discovery Timeline
- 2026-07-02 - CVE-2026-57755 published to NVD
- 2026-07-02 - Last updated in NVD database
Technical Details for CVE-2026-57755
Vulnerability Analysis
The Mosaic Gallery – Advanced Gallery plugin fails to properly neutralize user-supplied input before rendering it inside gallery output. A Contributor-authenticated attacker submits gallery content containing HTML or JavaScript payloads. When an administrator or visitor loads the affected page, the browser parses the injected markup and executes attacker-controlled script in the context of the site origin.
The vulnerability requires user interaction from the victim and produces a scope change, meaning script executes in a browsing context beyond the vulnerable component. Impact spans confidentiality, integrity, and availability at limited levels because the attacker acts through a victim session rather than directly against the server.
Root Cause
The root cause is missing or insufficient output escaping and input sanitization in gallery fields exposed to Contributor role users. WordPress role separation assumes Contributors cannot publish arbitrary HTML, but the plugin bypasses those safeguards by rendering attributes or content without applying esc_attr(), esc_html(), or wp_kses() filtering.
Attack Vector
The attack requires network access, low privileges (Contributor account), and victim interaction such as previewing or approving submitted content. The attacker crafts a gallery entry with a JavaScript payload embedded in a title, caption, or attribute field. When an administrator reviews the pending submission, the payload fires with administrative session cookies available to the same origin.
See the Patchstack Vulnerability Report for additional technical detail.
Detection Methods for CVE-2026-57755
Indicators of Compromise
- Gallery posts or attachments containing <script> tags, javascript: URIs, or event handler attributes such as onerror= and onload= in title, caption, or alt-text fields.
- Unexpected outbound HTTP requests from administrator browsers to attacker-controlled domains shortly after reviewing pending Contributor submissions.
- New administrator accounts or plugin installations following Contributor content approval workflows.
Detection Strategies
- Review the wp_posts and wp_postmeta tables for gallery entries containing HTML tags or JavaScript keywords submitted by Contributor role users.
- Inspect web server access logs for POST requests to admin-ajax.php or gallery endpoints containing URL-encoded script payloads.
- Deploy a Web Application Firewall (WAF) rule set that flags XSS patterns in WordPress plugin parameters.
Monitoring Recommendations
- Alert on creation or modification of gallery content by non-Editor accounts.
- Monitor administrator sessions for anomalous API calls issued immediately after loading pending post preview pages.
- Track plugin version inventory across WordPress fleets to identify installations still running 1.2.0 or earlier.
How to Mitigate CVE-2026-57755
Immediate Actions Required
- Update the Mosaic Gallery – Advanced Gallery plugin to a version later than 1.2.0 once the vendor releases a fix.
- Audit Contributor-level accounts and remove any that are inactive or unnecessary.
- Review all pending and published gallery content for injected scripts before promoting posts.
Patch Information
At the time of publication, the NVD entry references the Patchstack Vulnerability Report as the authoritative source. Administrators should consult the plugin's WordPress.org page for the current fixed version and apply updates through the WordPress admin dashboard.
Workarounds
- Disable the Mosaic Gallery – Advanced Gallery plugin until a patched release is installed.
- Restrict Contributor role assignments and require Editor-level review before rendering gallery content on public pages.
- Deploy a Content Security Policy (CSP) that blocks inline script execution to reduce the impact of stored XSS payloads.
# Configuration example
wp plugin deactivate mosaic-gallery-advanced-gallery
wp user list --role=contributor --fields=ID,user_login,user_email
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
