Which user privileges are required by a Copssh service account ?

Copssh versions 7 and higher use local system account as the service account and no further adjustments are necessary.

However, you may still prefer to use a dedicated service account (domain account for example). Make sure that the service account is member of local  Administrators group and have following user rights:

SeCreateTokenPrivilege

SeAssignPrimaryTokenPrivilege

SeIncreaseQuotaPrivilege

SeServiceLogonRight

Tools to set user rights: Domain Group Policy Management for domain members, Local Security Policy (secpol.msc) for local computers