GitLab Community and Enterprise Editions version 9.2 up to 10.4 are vulnerable to XSS because a lack of input validation in the milestones component leads to cross site scripting (specifically, data-milestone-id in the milestone dropdown feature). This is fixed in 10.6.3, 10.5.7, and 10.4.7.
The Auth0 integration in GitLab before 10.3.9, 10.4.x before 10.4.6, and 10.5.x before 10.5.6 has an incorrect omniauth-auth0 configuration, leading to signing in unintended users.