The security handlers in the Security component in Symfony in 2.7.x before 2.7.48, 2.8.x before 2.8.41, 3.3.x before 3.3.17, 3.4.x before 3.4.11, and 4.0.x before 4.0.11 have an Open redirect vulnerability when security.http_utils is inlined by a container. NOTE: this issue exists because of an incomplete fix for CVE-2017-16652.
The web application accepts a user-controlled input that specifies a link to an external site, and uses that link in a redirect.