A recent security flaw in FreePBX, the open-source PBX management system built around Asterisk, has surfaced as attackers increasingly exploit its SQL injection vulnerability to gain unauthorized database control and potentially execute arbitrary code.
The vulnerability, tracked as CVE-2025-57819, was first reported on August 28, 2025, through the FreePBX community advisory, warning administrators to restrict web interface access as active exploitation had begun.
Technical Analysis of the Exploit
The vulnerability lies within the admin/ajax.php endpoint of FreePBX, which fails to sanitize user input correctly passed through the brand parameter in the AJAX module interface.
Attackers can inject SQL commands directly into database queries by manipulating this parameter, allowing the insertion of malicious entries into the backend tables. One observed exploit request takes the form of:
GET /admin/ajax.php?module=FreePBX\modules\endpoint\ajax&command=model&template=x&model=model&brand=x' ;INSERT INTO cron_jobs (...) --
This injection modifies the cron_jobs table, which is responsible for managing scheduled system tasks, to include a command that creates and executes a web-accessible PHP file on the server.
The injected cron entry executes a Base64-decoded shell command every minute, writing a malicious PHP backdoor named /var/www/html/rspgf.php. The decoded payload writes the following file content:
php<?php header('x_poc: CVE-2025-57819'); echo shell_exec('uname -a'); unlink(__FILE__); ?>
Once the script runs, it discloses system information via the uname -a Command and then deletes itself. However, because the cron job persists, the file is regenerated every minute, rendering the self-deletion ineffective.
This persistence mechanism ensures ongoing attacker access even after attempts at cleanup.
Potential Impact and Mitigation
By leveraging such an injection, attackers can manipulate the FreePBX database to introduce scheduled tasks, alter configurations, or execute arbitrary system-level commands. These actions may lead to unauthorized call routing, service disruption, or complete system compromise.
PBX systems, by their nature, hold high-value telecom capabilities, making them attractive targets for toll fraud, impersonation, and call obfuscation attacks.
FreePBX maintainers have urged users to immediately patch and restrict administrative access to internal or VPN-only networks. Instances running outdated modules are particularly vulnerable.
Administrators are encouraged to audit the cron_jobs table for suspicious entries and investigate any recently created files within the /var/www/html/ directory.
Given ongoing exploitation observed in the wild, organizations using FreePBX should update to the latest secure build, deploy web application firewalls, and monitor outbound traffic for signs of script-triggered activity.
The incident serves as another reminder that unsecured administrative interfaces can become powerful entry points in telecommunication environments.
Find this Story Interesting! Follow us on Google News , LinkedIn and X to Get More Instant Updates
