Attack Chain

1. An attacker authenticates to the WordPress admin interface.
2. The attacker navigates to the HS Brand Logo Slider plugin settings.
3. The attacker attempts to upload a malicious file (e.g., a PHP webshell) disguised with an allowed extension (e.g., .jpg).
4. The client-side validation is bypassed by intercepting the upload request, commonly using a web proxy like Burp Suite.
5. The attacker modifies the filename within the intercepted request to change the file extension to .php.
6. The modified request is sent to the server, uploading the PHP webshell.
7. The attacker accesses the uploaded PHP webshell through a direct HTTP request to the /wp-content/plugins/ directory.
8. The attacker executes arbitrary commands on the server via the webshell, achieving remote code execution.

Impact

Successful exploitation of this vulnerability can lead to complete compromise of the affected WordPress website. Attackers can gain unauthorized access to sensitive data, modify website content, install malware, or use the compromised server as a launchpad for further attacks. Given the wide use of WordPress and its plugins, this vulnerability presents a significant threat to many websites. The CVSS v3.1 base score for this vulnerability is 8.8, indicating high severity.

Recommendation

• Upgrade to a patched version of the HS Brand Logo Slider plugin if available.
• Implement server-side file validation to prevent the upload of arbitrary file types.
• Monitor web server logs for suspicious requests to the /wp-content/plugins/ directory with .php extensions in the filename (see Sigma rule below).
• Apply the principle of least privilege to WordPress user accounts, limiting access to only necessary functions.
• Deploy the Sigma rule to detect attempts to upload PHP files to the logoupload parameter.