Vdesk Hangupphp3 Exploit -

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.

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: vdesk hangupphp3 exploit

| 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. | 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();