It was possible to guess/extract the Symfony's application secret (APP_SECRET). The secret was either guessed from a list of weak secrets or was extracted from the publicly accessible phpinfo page.

Using this secret it was possible to execute arbitrary PHP code using the ESI (Edge-Side Includes) functionality that is accessible at /_fragment.


It's recommended to disable ESI (Edge-Side Includes) and to change the Symfony's application secret (APP_SECRET).


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