Secure Automation: Achieving Least Privilege with SSH, Sudo, and Suid

Automation tools commonly require some level of escalated privilege in order to perform their functions, often including escalated privileges on remote machines. To achieve this, developers may choose to provide their tools with wide-ranging privileges on many machines rather than providing just the privileges required. For example, tools may be made setuid root, granting them full root privileges for their entire run. Administrators may also be tempted to create unrestricted, null-password, root-access SSH keys for their tools, creating trust relationships that can be abused by attackers. Most of all, with the complexity of today’s environments, it becomes harder for administrators to understand the far-reaching security implications of the privileges they grant their tools. In this paper we will discuss the principle of least privilege and its importance to the overall security of an environment. We will cover simple attacks against SSH, sudo and setuid and how to reduce the need for root-setuid using other techniques such as non-root setuid, setgid scripts and directories, sudo and sticky bits. We will demonstrate how to properly limit sudo access both for administrators and tools. Finally we will introduce several SSH techniques to greatly limit the risk of abuse including non-root keys, command keys and other key restrictions.