Affected versions
Symfony 2.7.0 to 2.7.50, 2.8.0 to 2.8.49, 3.4.0 to 3.4.25, 4.1.0 to 4.1.11 and 4.2.0 to 4.2.6 versions of the Symfony HttpFoundation component are affected by this security issue.
The issue has been fixed in Symfony 2.7.51, 2.8.50, 3.4.26, 4.1.12 and 4.2.7.
Note that no fixes are provided for Symfony 3.0, 3.1, 3.2, 3.3, and 4.0 as they are not maintained anymore.
Description
HTTP methods, from either the HTTP method itself or using the X-Http-Method-Override
header were previously returned as the method in question without validation being done on the string, meaning that they could be used in dangerous contexts when left unescaped.
Resolution
HTTP methods are now only allowed to contain ASCII letters (A-Z).
The patch for this issue is available here for branch 3.4.
Credits
I would like to thank mschop for reporting the issue and Nicolas Grekas for fixing it.