Unknown index "UsernamePasswordFormAuthenticve_index" in cron logfile - security issue?

Question

Today i noticed a really strange index and code dump in cron.log: UsernamePasswordFormAuthenticve_index is successfully finished

^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@
^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@t\\SwitchUserEvent' => __DIR__ . '/..' . '/symfony/symfony/src/Symfony/Component/Security/Http/Even
t/SwitchUserEvent.php',
        'Symfony\\Component\\Security\\Http\\Firewall' => __DIR__ . '/..' . '/symfony/symfony/src/Symfony/Component/Security/Http/Firewall.php',
        'Symfony\\Component\\Security\\Http\\FirewallMap' => __DIR__ . '/..' . '/symfony/symfony/src/Symfony/Component/Security/Http/FirewallMap.php',
        'Symfony\\Component\\Security\\Http\\FirewallMapInterface' => __DIR__ . '/..' . '/symfony/symfony/src/Symfony/Component/Security/Http/FirewallMapInterface.php',
        'Symfony\\Component\\Security\\Http\\Firewall\\AbstractAuthenticationListener' => __DIR__ . '/..' . '/symfony/symfony/src/Symfony/Component/Security/Http/Firewall/AbstractAuthenticationListener.php
',
        'Symfony\\Component\\Security\\Http\\Firewall\\AbstractPreAuthenticatedListener' => __DIR__ . '/..' . '/symfony/symfony/src/Symfony/Component/Security/Http/Firewall/AbstractPreAuthenticatedListener
.php',
        'Symfony\\Component\\Security\\Http\\Firewall\\AccessListener' => __DIR__ . '/..' . '/symfony/symfony/src/Symfony/Component/Security/Http/Firewall/AccessListener.php',
        'Symfony\\Component\\Security\\Http\\Firewall\\AnonymousAuthenticationListener' => __DIR__ . '/..' . '/symfony/symfony/src/Symfony/Component/Security/Http/Firewall/AnonymousAuthenticationListener.p
hp',
        'Symfony\\Component\\Security\\Http\\Firewall\\BasicAuthenticationListener' => __DIR__ . '/..' . '/symfony/symfony/src/Symfony/Component/Security/Http/Firewall/BasicAuthenticationListener.php',
        'Symfony\\Component\\Security\\Http\\Firewall\\ChannelListener' => __DIR__ . '/..' . '/symfony/symfony/src/Symfony/Component/Security/Http/Firewall/ChannelListener.php',
        'Symfony\\Component\\Security\\Http\\Firewall\\ContextListener' => __DIR__ . '/..' . '/symfony/symfony/src/Symfony/Component/Security/Http/Firewall/ContextListener.php',
        'Symfony\\Component\\Security\\Http\\Firewall\\DigestAuthenticationListener' => __DIR__ . '/..' . '/symfony/symfony/src/Symfony/Component/Security/Http/Firewall/DigestAuthenticationListener.php',
        'Symfony\\Component\\Security\\Http\\Firewall\\DigestData' => __DIR__ . '/..' . '/symfony/symfony/src/Symfony/Component/Security/Http/Firewall/DigestAuthenticationListener.php',
        'Symfony\\Component\\Security\\Http\\Firewall\\ExceptionListener' => __DIR__ . '/..' . '/symfony/symfony/src/Symfony/Component/Security/Http/Firewall/ExceptionListener.php',
        'Symfony\\Component\\Security\\Http\\Firewall\\ListenerInterface' => __DIR__ . '/..' . '/symfony/symfony/src/Symfony/Component/Security/Http/Firewall/ListenerInterface.php',
        'Symfony\\Component\\Security\\Http\\Firewall\\LogoutListener' => __DIR__ . '/..' . '/symfony/symfony/src/Symfony/Component/Security/Http/Firewall/LogoutListener.php',
        'Symfony\\Component\\Security\\Http\\Firewall\\RememberMeListener' => __DIR__ . '/..' . '/symfony/symfony/src/Symfony/Component/Security/Http/Firewall/RememberMeListener.php',
        'Symfony\\Component\\Security\\Http\\Firewall\\RemoteUserAuthenticationListener' => __DIR__ . '/..' . '/symfony/symfony/src/Symfony/Component/Security/Http/Firewall/RemoteUserAuthenticationListener.php',
        'Symfony\\Component\\Security\\Http\\Firewall\\SimpleFormAuthenticationListener' => __DIR__ . '/..' . '/symfony/symfony/src/Symfony/Component/Security/Http/Firewall/SimpleFormAuthenticationListener.php',
        'Symfony\\Component\\Security\\Http\\Firewall\\SimplePreAuthenticationListener' => __DIR__ . '/..' . '/symfony/symfony/src/Symfony/Component/Security/Http/Firewall/SimplePreAuthenticationListener.php',
        'Symfony\\Component\\Security\\Http\\Firewall\\SwitchUserListener' => __DIR__ . '/..' . '/symfony/symfony/src/Symfony/Component/Security/Http/Firewall/SwitchUserListener.php',
        'Symfony\\Component\\Security\\Http\\Firewall\\UsernamePasswordFormAuthenticationListener' => __DIR__ . '/..' . '/symfony/symfony/src/Symfony/Component/Security/Http/Firewall/
UsernamePasswordFormAuthenticve_index is successfully finished. Statistics: {"sum":0.0078999996185303,"count":1,"realmem":0,"emalloc":62416,"realmem_start":174063616,"emalloc_start":167677000} [] []

Does anyone know what happened here?

• What are all these "@^" for?
• I can't find any Symfony Security component (/symfony/symfony/src) in Magento?
• Is that e possible security breach and someone tries to use the symfony impersonate / switch-user function to gain privileges?

(Magento Version: 2.2.10)

Any help would appreciated