CVE-2026-77028: YOOtheme Zoo Joomla XSS Vulnerability

CVE-2026-77028 Overview

CVE-2026-77028 is a reflected cross-site scripting (XSS) and open redirect vulnerability in the YOOtheme Zoo extension for Joomla. The flaw resides in the submission redirect parameter and affects all versions of Zoo prior to 4.1.66. Attackers can craft a malicious URL that, when followed by an authenticated or unauthenticated user, executes attacker-controlled script in the victim's browser or redirects the user to an arbitrary external site.

The vulnerability is classified under CWE-79: Improper Neutralization of Input During Web Page Generation. It requires user interaction, typically through phishing, to trigger exploitation.

Critical Impact
Successful exploitation enables session theft, credential harvesting through injected forms, and phishing redirection through the trusted Joomla site domain.

Affected Products

YOOtheme Zoo Joomla extension versions prior to 4.1.66
Joomla installations using the Zoo content application builder
Sites exposing the Zoo submission workflow with the vulnerable redirect parameter

Discovery Timeline

2026-08-21 - CVE-2026-77028 published to NVD
2026-08-26 - Last updated in NVD database

Technical Details for CVE-2026-77028

Vulnerability Analysis

The Zoo extension provides a content submission workflow that accepts a redirect parameter to send users to a designated URL after form submission. The extension fails to properly neutralize input passed through this parameter before reflecting it back into the response. This creates two distinct attack paths from a single sink.

For the reflected XSS path, an attacker injects JavaScript payloads into the submission redirect parameter. When the victim visits the crafted URL, the extension renders the untrusted value in an HTML context, and the browser executes the attacker's script under the origin of the hosting Joomla site.

For the open redirect path, the same parameter accepts external URLs without domain allowlisting. Attackers use the trusted Joomla domain as a launching point for phishing, credential harvesting, and malware distribution campaigns.

Root Cause

The root cause is missing input validation and output encoding on the submission redirect parameter. The extension trusts the parameter for both navigation and page rendering without applying context-appropriate sanitization. A domain allowlist for the redirect target and HTML entity encoding on reflected output would eliminate both issues.

Attack Vector

Exploitation requires a victim to click a crafted link. Attackers typically deliver the link through email phishing, social media, or embedded iframes. The attack vector is network-based, requires no privileges, and depends on user interaction. See the YOOtheme Official Website for vendor advisory details.

The vulnerability manifests when the Zoo submission handler processes the redirect query parameter. Because no verified proof-of-concept has been published, technical details on the exact injection sink are limited to vendor documentation.

Detection Methods for CVE-2026-77028

Indicators of Compromise

HTTP requests to Zoo submission endpoints containing redirect= parameters with encoded <script>, javascript:, or onerror= payloads
Referer headers pointing to external domains followed by redirects through the Joomla site to unfamiliar destinations
Web server access logs showing repeated requests to Zoo submission URLs with unusually long or encoded query strings

Detection Strategies

Inspect web application firewall (WAF) logs for reflected XSS signatures targeting the Zoo submission redirect parameter
Correlate outbound redirects from Joomla-hosted URLs against a domain reputation feed to surface open redirect abuse
Review Joomla component version inventory to identify Zoo installations below 4.1.66

Monitoring Recommendations

Enable verbose logging on the Joomla web tier and forward events to a centralized analytics platform for query-based hunting
Alert on user reports of unexpected redirects or credential prompts originating from the site
Monitor client-side telemetry, such as Content Security Policy (CSP) violation reports, for injected script execution

How to Mitigate CVE-2026-77028

Immediate Actions Required

Upgrade the YOOtheme Zoo extension to version 4.1.66 or later on all Joomla installations
Audit existing submission forms and templates for custom code that references the redirect parameter
Deploy or tune WAF rules to block XSS payloads and external URLs in the Zoo redirect parameter

Patch Information

YOOtheme addresses the issue in Zoo 4.1.66. Administrators should apply the update through the Joomla extension manager and verify the installed version after the upgrade. Consult the YOOtheme Official Website for release notes and download links.

Workarounds

Restrict access to Zoo submission endpoints through authentication or IP allowlisting until patching completes
Enforce a strict Content Security Policy that disallows inline scripts and limits allowed script sources
Implement a server-side redirect allowlist at the reverse proxy layer to block off-domain redirect targets

bash

# Example nginx rule to block external redirect targets on Zoo submission URLs
location ~* /index\.php {
    if ($arg_redirect ~* "^https?://(?!yourdomain\.com)") {
        return 403;
    }
}