This indicates an attack attempt to exploit a Command Injection vulnerability in DrayTek Vigor devices.
The vulnerability is due to insufficient sanitizing of user supplied inputs. A remote attacker may be able to exploit this to execute arbitrary commands within the context of the application, via a crafted HTTP request.
Vigor2960 before v1.5.1
Vigor300B before v1.5.1
Vigor3900 before v1.5.1
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.