CVE-2017-16790: Ensure that submitted data are uploaded files
Symfony 2.7.0 to 2.7.37, 2.8.0 to 2.8.30, 3.2.0 to 3.2.13, and 3.3.0 to 3.3.12 versions of the Symfony Form component are affected by this security issue.
The issue has been fixed in Symfony 2.7.38, 2.8.31, 3.2.14, 3.3.13, 3.4-BETA5, and 4.0-BETA5.
Note that no fixes are provided for Symfony 3.0 and 3.1 as they are not maintained anymore.
When a form is submitted by the user, the request handler classes of the Form component
merge POST data (known as the
$_POST array in plain PHP) and uploaded files data
(known as the
$_FILES array in plain PHP) into one array. This big array forms the
data that are then bound to the form. At this stage there is no difference anymore between
submitted POST data and uploaded files.
A user can send a crafted HTTP request where the value of a
FileType is sent as
normal POST data that could be interpreted as a locale file path on the server-side (for
file:///etc/passwd). If the application did not perform any additional checks
about the value submitted to the
FileType, the contents of the given file on the server
could have been exposed to the attacker.
As part of the fix, a new
isFileUpload() method was added to the
This method is called by the
FileType to verify that the handled data is an uploaded file.
The patch for this issue is available here.
I would like to thank Ondrej Exner for reporting this security issue, Christian Flothmann for providing a fix, and the Symfony Core Team for reviewing the patch.