Vdesk Hangupphp3 Exploit -

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.

For the vDesk HangupPHP3 exploit to be viable, the target system must meet the following criteria:

VDesk stored session data in flat files within /tmp/ or /vdesk/sessions/. The hangup.php3 script often accepted a session_id via GET or POST without sufficient sanitization. vdesk hangupphp3 exploit

A typical vulnerable code block in hangup.php3 might look like this (reconstructed for educational analysis):

// VULNERABLE CODE - DO NOT USE
$session_id = $HTTP_GET_VARS['sess'];
$ticket_id = $HTTP_GET_VARS['ticket'];
include("/vdesk/sessions/sess_" . $session_id);
// ... then close the ticket

Because $session_id was directly concatenated into an include() statement, an attacker could supply: The hangup

/vdesk/hangup.php3?sess=../../../../etc/passwd%00

If PHP3’s magic quotes were off, this would read system files. But the real goal was RCE.

The "vdesk hangupphp3 exploit" appears to be a targeted denial-of-service (DoS) vector rather than a Remote Code Execution (RCE) breach. Based on the naming convention, the exploit targets the hangup event handler within a PHP3-era logic gate (or a legacy wrapper in modern VOIP/PBX systems emulating PHP3 behavior). If PHP3’s magic quotes were off, this would

The exploit attempts to trigger a race condition by sending malformed SIP headers or HTTP POST payloads to the hangup.php3 endpoint during an active session termination. The goal is to force the backend process to retain a "zombie" thread while the frontend believes the session has ended.

In a controlled sandbox environment, replicating the exploit yielded inconsistent results.

Since direct code inclusion was often blocked, attackers used session file poisoning:

This technique is precisely what security researchers in the mid-2000s labeled the "vdesk hangupphp3 exploit."