This Metasploit module provides remote code execution against GitLab Community Edition (CE) and Enterprise Edition (EE). It combines an arbitrary file read to extract the Rails secret_key_base, and gains remote code execution with a deserialization vulnerability of a signed experimentation_subject_id cookie that GitLab uses internally for A/B testing. Note that the arbitrary file read exists in GitLab EE/CE 8.5 and later, and was fixed in 12.9.1, 12.8.8, and 12.7.8. However, the RCE only affects versions 12.4.0 and above when the vulnerable experimentation_subject_id cookie was introduced. Tested on GitLab 12.8.1 and 12.4.0.