A logged in back end user can include arbitrary PHP files by manipulating an URL parameter. Since Contao does not allow to upload PHP files in the file manager, the attack is limited to the existing PHP files on the server.

References

• https://nvd.nist.gov/vuln/detail/CVE-2017-10993
• https://contao.org/en/news/contao-3_5_28.html
• https://contao.org/en/news/contao-4_4_1.html
• https://github.com/FriendsOfPHP/security-advisories/blob/master/contao/contao/CVE-2017-10993.yaml
• https://github.com/FriendsOfPHP/security-advisories/blob/master/contao/core-bundle/CVE-2017-10993.yaml
• https://github.com/FriendsOfPHP/security-advisories/blob/master/contao/core/CVE-2017-10993.yaml