Vdesk Hangupphp3 Exploit May 2026
POST /telephony/hangup.php3 HTTP/1.1 Host: target.vdesk.com Cookie: PHPSESSID=malicious123 Content-Type: application/x-www-form-urlencoded call_id=12345&force=1&sig_type=SIGHUP The hangup.php3 script receives the SIGHUP signal. Because the script uses pcntl_signal() without pcntl_signal_dispatch() in a safe context, it triggers an asynchronous fork. The parent process writes to the session file while the child process—intended to clean up call resources—attempts to write a log entry. This creates a race condition. Phase 4: Session Desynchronization During the race, both processes try to call session_start() simultaneously. PHP’s default file-based session handler is not atomic. One process obtains a write lock, but the other executes session_write_close() prematurely. The session file becomes corrupted, containing partially unserialized data. Phase 5: Code Injection via Session Data The attacker then sends a second crafted request containing PHP serialized payloads within session variables (e.g., $_SESSION['caller_id'] = "<?php system($_GET['cmd']); ?>" ). The corrupted session handler interprets the closing ?> tag as a legitimate PHP delimiter, executing the injected code upon the next page load.
| Impact Area | Description | |-------------|-------------| | | Full control over the web server, allowing malware upload, data exfiltration, or pivoting to internal networks. | | Denial of Service | The race condition can corrupt session files for all users, effectively locking out entire helpdesk teams. | | Call Recording Theft | Attackers can download unencrypted call recordings stored by vDesk. | | Privilege Escalation | From a low-privileged agent account to the web server user, then potentially root via local exploits. | | VoIP Fraud | Using the compromised session, attackers can initiate outbound calls through the PBX integration. | vdesk hangupphp3 exploit
At this point, the attacker achieves remote code execution with the privileges of the web server user (e.g., www-data or apache ). While the vDesk HangupPHP3 exploit targets legacy systems, its consequences are severe: POST /telephony/hangup
Introduction In the evolving landscape of web application security, few vulnerabilities carry the dual threat of remote code execution (RCE) and denial-of-service (DoS) as insidiously as the class of exploits targeting session management flaws. Among these, the exploit colloquially known as "vDesk HangupPHP3" has emerged as a significant concern for legacy virtual desktop infrastructures and PHP-based ticketing systems. This creates a race condition
if (!isset($_SESSION['authenticated']) || $_SESSION['authenticated'] !== true) header('HTTP/1.0 403 Forbidden'); exit();
