CVE-2026-77996 Overview
CVE-2026-77996 is a stored cross-site scripting (XSS) vulnerability in the YOOtheme Pro extension for Joomla. The flaw affects YOOtheme Pro versions 1.0.0 through 5.0.41. The extension fails to escape input in the location custom field, allowing an authenticated user with elevated privileges to inject JavaScript that executes when other users view the affected content. The issue is classified under CWE-79 (Improper Neutralization of Input During Web Page Generation).
Critical Impact
An authenticated attacker with high privileges can persist malicious script into the location custom field, executing arbitrary JavaScript in the browsers of administrators or other users who load the rendered page.
Affected Products
- YOOtheme Pro for Joomla versions 1.0.0 through 5.0.41
- Joomla sites using the YOOtheme Pro page builder with location custom fields
- Deployments where privileged accounts can author content containing custom field values
Discovery Timeline
- 2026-08-25 - CVE-2026-77996 published to NVD
- 2026-08-26 - Last updated in NVD database
Technical Details for CVE-2026-77996
Vulnerability Analysis
The vulnerability resides in how YOOtheme Pro handles the location custom field value during page rendering. User-supplied content stored in this field is written into the HTML output without proper escaping. When the affected page is loaded, the browser interprets the injected payload as executable script rather than inert text.
Exploitation requires an authenticated user with permission to author or edit content containing the location field. This aligns with the CVSS attack requirements indicating high privileges are needed. Because the payload persists in stored content, every subsequent visitor to the affected page becomes a target, including site administrators.
The stored nature of the flaw distinguishes it from reflected XSS. The attacker only needs to submit the payload once, and it remains active until an administrator removes it. Successful exploitation can lead to session token theft, forced administrative actions, defacement, or delivery of secondary payloads against site visitors.
Root Cause
The root cause is missing output encoding on the location custom field. The extension trusts stored field values and inserts them directly into the DOM without applying HTML entity encoding or context-aware sanitization. Standard Joomla templating helpers such as htmlspecialchars or the framework's escaping API are not applied to this specific field path.
Attack Vector
An authenticated privileged user submits a crafted payload into the location custom field of a YOOtheme Pro-managed item. The payload is stored in the Joomla database. When any user, including higher-privileged administrators, loads a page that renders that field, the injected JavaScript executes in the context of the site's origin. This enables cookie theft, CSRF chaining, and privilege escalation against administrator sessions.
No verified public proof-of-concept code is available for this issue. Refer to the YOOtheme Official Website for vendor advisories and update notes.
Detection Methods for CVE-2026-77996
Indicators of Compromise
- Unexpected <script> tags, on* event handlers, or javascript: URIs stored within the location custom field values in the Joomla database
- Administrator browser sessions issuing unusual authenticated requests, such as user creation or extension installation, immediately after viewing content that uses YOOtheme Pro location fields
- Outbound HTTP requests from administrator browsers to unfamiliar domains sourced from pages rendered by YOOtheme Pro
Detection Strategies
- Query the Joomla #__fields_values table for custom field entries containing HTML tag characters, event handler attributes, or encoded script markers
- Inspect rendered HTML of pages using the location field for script content that does not originate from the site's templates or approved plugins
- Correlate content edits by privileged users against subsequent administrator session anomalies to identify potential stored payload activity
Monitoring Recommendations
- Enable web server access logging and alert on administrator-authenticated POST requests originating from pages containing YOOtheme Pro custom fields
- Deploy a Content Security Policy (CSP) in report-only mode to surface inline script executions that violate policy
- Track changes to Joomla user accounts, extensions, and template files for signs of post-exploitation persistence
How to Mitigate CVE-2026-77996
Immediate Actions Required
- Upgrade YOOtheme Pro to a version later than 5.0.41 once the vendor publishes a fixed release
- Audit all existing location custom field values for HTML or JavaScript content and remove suspicious entries
- Review and reduce the number of accounts with permission to edit YOOtheme Pro content items
Patch Information
Consult the YOOtheme Official Website for the current patched release and vendor guidance. Apply the fixed version across all Joomla instances using YOOtheme Pro. After patching, re-render affected pages to confirm stored values are properly encoded in the output HTML.
Workarounds
- Restrict edit permissions on content items using YOOtheme Pro custom fields to a minimal set of trusted administrators
- Enforce a strict Content Security Policy that blocks inline scripts and disallows untrusted script sources
- Deploy a web application firewall rule that inspects submissions to the location field and blocks payloads containing script markers or event handlers
# Example CSP header to reduce stored XSS impact
Header set Content-Security-Policy "default-src 'self'; script-src 'self'; object-src 'none'; base-uri 'self'; frame-ancestors 'self'"
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
