This indicates an attack attempt to exploit a Code Injection Vulnerability in Gitlab-shell.
The vulnerability is due to an input validation error when the vulnerable software handles a crafted HTTP request. A remote attacker could exploit this to execute arbitrary code within the context of target application, via a HTTP request.
Gitlab-shell 6.2 and prior
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.