Attack Chain

1. An authenticated attacker obtains valid credentials or an API token with file upload permissions (e.g., to /api/3/uploadfiles or /api/3/attachedfiles).
2. The attacker crafts an HTTP POST request to a vulnerable upload endpoint (e.g., /api/3/uploadfiles), submitting a file with a malicious filename containing path traversal sequences, such as ../Dinamic/Assets/.htaccess.
3. The UploadedFile::move() method in FacturaScripts processes this filename without proper sanitization, concatenating it with the base directory, causing the .htaccess file to be written into the Dinamic/Assets/ directory.
4. The uploaded .htaccess file contains a directive like AddType application/x-httpd-php .png, instructing Apache to parse .png files as PHP scripts within that directory.
5. The attacker then initiates a second file upload using the same path traversal technique, delivering a file named ../Dinamic/Assets/x.png containing arbitrary PHP code (e.g., <?php phpinfo(); ?>).
6. The PHP payload is written to Dinamic/Assets/x.png due to the path traversal vulnerability.
7. The default Apache configuration for FacturaScripts (from htaccess-sample) excludes Dinamic/Assets/ from index.php rewrite rules, meaning files in this directory are served directly by Apache.
8. The attacker accesses https://target/Dinamic/Assets/x.png via a web browser or HTTP request, causing the Apache web server to execute the uploaded PHP code as the web-server user, resulting in remote code execution.

Impact

Successful exploitation of GHSA-hgjx-r89m-m7v4 allows an authenticated attacker to achieve full remote code execution (RCE) as the web-server user. This includes the ability to execute arbitrary commands, steal data, deface the website, or compromise the server hosting FacturaScripts. The attacker can also inject client-side script by overwriting legitimate JavaScript or CSS files within the Dinamic/Assets/ directory, leading to session takeover for administrators or other users on subsequent page loads. The vulnerability affects a wide range of users, as even non-administrative roles often possess the necessary upload permissions.

Recommendation

• Deploy the provided Sigma rules to your SIEM solution to detect attempts to upload malicious .htaccess or PHP files using path traversal.
• Monitor webserver logs for HTTP POST requests to /api/3/uploadfiles, /api/3/attachedfiles, or other file upload endpoints that include ../ sequences in the filename or cs-uri-query.
• Patch FacturaScripts to a version greater than 2026.2 immediately upon availability of a fix, as specified in the GitHub Security Advisory GHSA-hgjx-r89m-m7v4.
• Implement strong logging for webserver activity, particularly for POST requests and file uploads, to enable detection of the described attack chain.
• Ensure server configurations enforce least privilege for the web-server user to minimize potential damage from RCE.