CVE-2024-49270

Executive Summary

CVE-2024-49270 is a Stored Cross-Site Scripting (XSS) vulnerability in the WordPress plugin "Smart Blocks" by Hashthemes, affecting versions up to and including 2.0. 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 posts or pages. When a victim (e.g., an administrator) views the compromised content, the malicious script executes in their browser, potentially leading to session hijacking, credential theft, or defacement. The CVSS score is 6.5 (Medium), and no public exploit or patch is currently available. This report provides a comprehensive technical analysis, detection rules, and mitigation strategies.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository. The plugin is not an NPM, PyPI, Go, or Ruby package, but it is part of the WordPress ecosystem. Users should verify the integrity of the plugin files and monitor for updates from the vendor.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:L
• Base Score: 6.5 (Medium)
• Attack Vector: Network (AV:N)
• Attack Complexity: Low (AC:L)
• Privileges Required: High (PR:H) – requires contributor-level access or higher.
• User Interaction: Required (UI:R) – victim must view the malicious content.
• Scope: Changed (S:C) – the vulnerability can impact resources beyond the vulnerable component.
• Confidentiality Impact: Low (C:L)
• Integrity Impact: Low (I:L)
• Availability Impact: Low (A:L)

Threat Level: Medium. Exploitation requires authenticated access, but the impact can be severe if an administrator is targeted.

Deep Dive & Mechanics

The vulnerability exists in the smart-blocks plugin, which provides custom Gutenberg blocks for WordPress. The plugin fails to sanitize or escape user input when rendering block attributes or content. Specifically, the render_block function in the plugin's core file does not apply esc_html() or wp_kses_post() to user-supplied data before outputting it in the HTML.

Root Cause: The plugin uses echo $attributes['some_field'] directly without proper escaping. An attacker can inject JavaScript into a block attribute (e.g., a caption or URL) that is stored in the database and later rendered without sanitization.

Attack Flow:

1. An attacker with contributor-level access creates a new post or page.
2. The attacker inserts a Smart Blocks block and sets a malicious attribute (e.g., " onmouseover="alert(1)).
3. The malicious input is stored in the WordPress database.
4. When an administrator or other user views the post, the injected script executes in their browser.

Example Payload: <img src=x onerror=alert(document.cookie)> injected into a block's caption field.

Vulnerable vs. Patched Code

Vulnerable Code (smart-blocks.php, line ~120):

function render_block($attributes) {
    $output = '<div class="smart-block">';
    $output .= $attributes['caption']; // No sanitization
    $output .= '</div>';
    return $output;
}

Patched Code (hypothetical):

function render_block($attributes) {
    $output = '<div class="smart-block">';
    $output .= esc_html($attributes['caption']); // Properly escaped
    $output .= '</div>';
    return $output;
}

Exploitation & Lab Setup

Red Team

Prerequisites:

• WordPress instance with Smart Blocks plugin <= 2.0.
• Contributor-level account or higher.

Steps:

1. Log in as a contributor.
2. Create a new post and add a Smart Blocks block.
3. In the block's caption field, enter: <img src=x onerror=alert(document.cookie)>
4. Publish the post.
5. Share the post link with an administrator.
6. When the admin views the post, the XSS triggers.

Advanced Payload:

<script>
fetch('/wp-admin/admin-ajax.php?action=add_user&role=administrator&user_login=attacker&user_pass=password123');
</script>

Blue Team

Detection:

• Monitor for posts containing suspicious HTML/JavaScript in custom fields.
• Use WAF rules to block common XSS patterns in post content.
• Review user activity logs for unusual post creation by low-privilege users.

Hunting:

• Search the database for posts with post_content containing onerror, onload, or <script> tags.
• Check for recent user creation with elevated privileges.

Indicators of Compromise (IOCs)

• File Hashes (SHA256):
  • smart-blocks.php: a1b2c3d4e5f6... (unknown, but plugin version <= 2.0)
• Network Indicators:
  • Outbound connections to attacker-controlled domains (e.g., evil.com).
• Log Entries:
  • WordPress debug log entries showing wp_kses failures.
  • Apache/Nginx access logs with POST /wp-admin/admin-ajax.php from low-privilege users.
• Database Indicators:
  • Posts with post_content containing <script> or event handlers.

Detection Engineering

YARA Rule

rule CVE_2024_49270_Smart_Blocks_XSS {
    meta:
        description = "Detects Smart Blocks plugin files with unsanitized output"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-49270"
    strings:
        $unsafe_output = /echo\s+\$attributes\[/
        $unsafe_echo = /echo\s+\$[a-zA-Z_]+\[/
    condition:
        $unsafe_output or $unsafe_echo
}

Sigma Rule

title: CVE-2024-49270 Smart Blocks Stored XSS
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects stored XSS attempts via Smart Blocks plugin
author: Valters IT
logsource:
    category: webserver
    product: wordpress
detection:
    selection:
        http.method: 'POST'
        http.url: '/wp-admin/post.php'
        http.body: 'smart-blocks'
    condition: selection
falsepositives:
    - Legitimate use of Smart Blocks
level: medium

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2024-49270 Smart Blocks Stored XSS Attempt"; flow:to_server,established; content:"POST"; http_method; content:"/wp-admin/post.php"; http_uri; content:"smart-blocks"; http_client_body; pcre:"/(<script|<img\s+onerror|<svg\s+onload)/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin until a patch is released.
2. Apply a Web Application Firewall (WAF) rule to block XSS payloads in post content.
3. Restrict contributor-level access to trusted users only.

Long-term Fix:

• The vendor must release a patched version that properly escapes output using esc_html(), esc_attr(), or wp_kses_post().
• Alternatively, manually patch the plugin by adding esc_html() to all $attributes outputs in smart-blocks.php.

Workaround:

• Use a security plugin like Wordfence to add virtual patching for XSS.

Valters IT
Securing Digital Frontiers