PHPUnit is a programmer-oriented testing framework for PHP. It is an instance of the xUnit architecture for unit testing frameworks.
When PHPUnit is installed in a production environment via composer and these modules are in a web accessible directory, the eval-stdin.php file in PHPUnit contains vulnerable statements that trigger the vulnerability.
A remote attacker could possibly execute arbitrary PHP code or cause a Denial of Service condition.
There are several ways to fix or mitigate this vulnerability:
Remove PHPUnit from the production environment.
Manually apply the patch.
Disable direct access to the composer packages by placing .htaccess file to /vendor folder.
All PHPUnit users should upgrade to the latest version:
# emerge --sync # emerge --ask --oneshot --verbose ">=dev-php/phpunit-5.7.15-r1"