An issue was discovered in PHP 7.3.x before 7.3.0alpha3, 7.2.x before 7.2.8, and before 7.1.20. The php-fpm master process restarts a child process in an endless loop when using program execution functions (e.g., passthru, exec, shell_exec, or system) with a non-blocking STDIN stream, causing this master process to consume 100% of the CPU, and consume disk space with a large volume of error logs, as demonstrated by an attack by a customer of a shared-hosting facility.
https://bugs.php.net/bug.php?id=70185
https://bugs.php.net/bug.php?id=73342https://github.com/php/php-src/pull/3287
https://bugs.php.net/bug.php?id=75968
https://github.com/php/php-src/blob/PHP-7.1.20/NEWS#L20-L22
https://github.com/php/php-src/commit/69dee5c732fe982c82edb17d0dbc3e79a47748d8
https://usn.ubuntu.com/3766-1/
Source: MITRE
Published: 2018-02-19
Updated: 2020-02-19
Type: CWE-400
Base Score: 6.8
Vector: AV:N/AC:L/Au:S/C:N/I:N/A:C
Impact Score: 6.9
Exploitability Score: 8
Severity: MEDIUM
Base Score: 6.5
Vector: CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Impact Score: 3.6
Exploitability Score: 2.8
Severity: MEDIUM