CVE-2023-6742

Executive Summary

CVE-2023-6742 is a medium-severity vulnerability affecting the Envira Photo Gallery WordPress plugin, versions up to and including 1.8.7.1. The flaw resides in the envira_gallery_insert_images function, which lacks proper capability checks. This allows authenticated attackers with Contributor-level access or higher to modify galleries on other users' posts without authorization. The vulnerability is classified as an improper capability check (CWE-862) and has a CVSS score of 4.3 (Medium). No public proof-of-concept (PoC) or exploit code has been released, and the patch status remains unknown. The EPSS score is 0.0%, indicating a low probability of exploitation in the wild.

Supply Chain & Package Security

This vulnerability is specific to the WordPress ecosystem and the Envira Photo Gallery plugin. It is not related to NPM, PyPI, Go, or Ruby packages. The plugin is distributed via the WordPress plugin repository and third-party marketplaces. Users should verify the integrity of their plugin files and ensure they are sourced from trusted channels.

CVSS Breakdown & Threat Level

• CVSS Score: 4.3 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: Low (Contributor-level)
• User Interaction: None
• Scope: Unchanged
• Confidentiality Impact: None
• Integrity Impact: Low
• Availability Impact: None

The threat level is considered medium due to the low privileges required and the potential for unauthorized modification of gallery content on other users' posts. However, the lack of public exploits and low EPSS score reduce immediate risk.

Deep Dive & Mechanics

The vulnerability exists in the envira_gallery_insert_images function, which is responsible for inserting images into galleries. The function fails to perform a proper capability check, allowing any authenticated user with Contributor-level access or higher to call it. This enables an attacker to modify galleries belonging to other users, potentially inserting malicious or inappropriate images.

The root cause is the absence of a current_user_can() check or similar authorization mechanism. The function likely relies on the wp_verify_nonce() function for CSRF protection but does not verify that the user has the necessary capabilities to edit the target gallery.

Vulnerable vs. Patched Code

Vulnerable Code (<= 1.8.7.1):

function envira_gallery_insert_images() {
    // No capability check
    $gallery_id = intval($_POST['gallery_id']);
    $images = $_POST['images'];
    // Insert images into gallery
    update_post_meta($gallery_id, '_eg_gallery_data', $images);
}

Patched Code (Hypothetical):

function envira_gallery_insert_images() {
    // Proper capability check
    if (!current_user_can('edit_post', $gallery_id)) {
        wp_die('Unauthorized');
    }
    $gallery_id = intval($_POST['gallery_id']);
    $images = $_POST['images'];
    // Insert images into gallery
    update_post_meta($gallery_id, '_eg_gallery_data', $images);
}

The patched version adds a current_user_can('edit_post', $gallery_id) check to ensure the user has permission to edit the specific gallery post.

Exploitation & Lab Setup

Red Team

To exploit this vulnerability, an attacker with Contributor-level access can craft a POST request to the WordPress admin-ajax.php endpoint with the action envira_gallery_insert_images. The request must include the target gallery ID and the images to be inserted.

Example Exploit Request:

POST /wp-admin/admin-ajax.php HTTP/1.1
Host: target-wordpress-site.com
Content-Type: application/x-www-form-urlencoded
Cookie: wordpress_logged_in_...

action=envira_gallery_insert_images&gallery_id=123&images[]=malicious_image_url

Blue Team

To detect exploitation attempts, monitor for unusual POST requests to admin-ajax.php with the action parameter set to envira_gallery_insert_images. Additionally, log all modifications to gallery post meta data and alert on changes made by users who do not own the gallery.

Detection Steps:

1. Enable logging of all AJAX requests in WordPress.
2. Monitor for envira_gallery_insert_images action from non-admin users.
3. Review gallery changes for unauthorized image insertions.

Indicators of Compromise (IOCs)

• Network: POST requests to /wp-admin/admin-ajax.php with action=envira_gallery_insert_images
• File: Modified _eg_gallery_data post meta for galleries not owned by the modifying user
• Log: WordPress debug log entries showing unauthorized gallery modifications
• User: Contributor-level accounts making AJAX requests to modify galleries

Detection Engineering

YARA Rule

rule CVE_2023_6742_Envira_Gallery_Unauthorized_Modification {
    meta:
        description = "Detects exploitation attempts of CVE-2023-6742 in Envira Photo Gallery plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2023-6742"
    strings:
        $ajax_action = "envira_gallery_insert_images"
        $gallery_id = "gallery_id"
        $images = "images"
    condition:
        $ajax_action and $gallery_id and $images
}

Sigma Rule

title: CVE-2023-6742 Envira Gallery Unauthorized Modification
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects unauthorized gallery modification attempts via envira_gallery_insert_images
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: 'action=envira_gallery_insert_images'
    condition: selection
falsepositives:
    - Legitimate gallery updates by authorized users
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2023-6742 Envira Gallery Unauthorized Modification"; flow:to_server,established; content:"POST"; http_method; content:"/wp-admin/admin-ajax.php"; http_uri; content:"action=envira_gallery_insert_images"; http_client_body; classtype:attempted-user; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Action: Disable the Envira Photo Gallery plugin until a patched version is released.
2. Workaround: Implement a custom capability check by adding a filter to the envira_gallery_insert_images function.
3. Long-term: Monitor the plugin vendor's website for updates and apply the patch as soon as it becomes available.
4. User Education: Restrict Contributor-level access to trusted users only.
5. Web Application Firewall (WAF): Create a rule to block POST requests to admin-ajax.php with action=envira_gallery_insert_images from non-admin users.

Valters IT
Securing Digital Ecosystems