Affected versions
Symfony 2.7.0 to 2.7.49, 2.8.0 to 2.8.48, 3.0.0 to 3.4.19, 4.0.0 to 4.0.14, 4.1.0 to 4.1.8 and 4.2.0 versions of the Symfony Form component are affected by this security issue.
The issue has been fixed in Symfony 2.7.50, 2.8.49, 3.4.20, 4.0.15, 4.1.9 and 4.2.1.
Note that no fixes are provided for Symfony 3.0, 3.1, 3.2 and 3.3 as they are not maintained anymore.
Description
Using backslashes in the _failure_path input field of login forms, one can work around the redirection target restrictions and effectively redirect the user to any domain after login.
Resolution
The regular expression filtering redirection targets has been updated to account for a mix of forward and backward slashes.
The patch for this issue is available here for branch 2.7.
Credits
I would like to thank the EC-CUBE Dev Team for reporting the issue and Christian Flothmann for fixing it.
Useful information, by activating the always_use_default_target_path within the login configuration you will actively mitigate this issue for logins (in older Symfony versions), as when this is set to true the redirect for the login will always be forwarded to /
This post refers to the Symfony Form component, but it should be the Security component, right?