GitLab before 8.14.9, 8.15.x before 8.15.6, and 8.16.x before 8.16.5 has XSS via a SCRIPT element in an issue attachment or avatar that is an SVG document.
Multiple versions of GitLab expose sensitive user credentials when assigning a user to an issue or merge request. A fix was included in versions 8.15.8, 8.16.7, and 8.17.4, which were released on March 20th 2017 at 23:59 UTC.
The impersonate feature in Gitlab 8.7.0, 8.6.0 through 8.6.7, 8.5.0 through 8.5.11, 8.4.0 through 8.4.9, 8.3.0 through 8.3.8, and 8.2.0 through 8.2.4 allows remote authenticated users to "log in" as any other user via unspecified vectors.