Citrix Virtual Apps and Desktop 7.x Linux Virtual Delivery Agent Security Technical Implementation Guide

Application management includes the ability to control the number of users and user sessions that utilize an application. Limiting the number of allowed users and sessions per user is helpful in limiting risks related to DoS attacks. This requirement may be met via the application or by utilizing information system session control provided by a web server with specialized session management capabilities. If it has been specified that this requirement will be handled by the application, the capability to limit the maximum number of concurrent single user sessions must be designed and built into the application. This requirement addresses concurrent sessions for information system accounts and does not address concurrent sessions by single users via multiple system accounts. The maximum number of concurrent sessions should be defined based upon mission needs and the operational environment for each system.

A session time-out lock is a temporary action taken when a user stops work and moves away from the immediate physical vicinity of the information system but does not log out because of the temporary nature of the absence. Rather than relying on the user to manually lock their application session prior to vacating the vicinity, applications need to be able to identify when a user's application session has idled and take action to initiate the session lock. The session lock is implemented at the point where session activity can be determined and/or controlled. This is typically at the operating system-level and results in a system lock, but may be at the application-level where the application interface window is secured instead.

It is detrimental for applications to provide, or install by default, functionality exceeding requirements or mission objectives. These unnecessary capabilities or services are often overlooked and therefore may remain unsecured. They increase the risk to the platform by providing additional attack vectors. Applications are capable of providing a wide variety of functions and services. Some of the functions and services, provided by default, may not be necessary to support essential organizational operations (e.g., key missions, functions). Examples of non-essential capabilities include, but are not limited to, advertising software or browser plug-ins not related to requirements or providing a wide array of functionality not required for every mission but cannot be disabled.

In order to prevent unauthorized connection of devices, unauthorized transfer of information, or unauthorized tunneling (i.e., embedding of data types within data types), organizations must disable or restrict unused or unnecessary physical and logical ports/protocols on information systems. Applications are capable of providing a wide variety of functions and services. Some of the functions and services provided by default may not be necessary to support essential organizational operations. Additionally, it is sometimes convenient to provide multiple services from a single component (e.g., email and web services; however, doing so increases risk over limiting the services provided by any one component. To support the requirements and principles of least functionality, the application must support the organizational requirements providing only essential capabilities and limiting the use of ports, protocols, and/or services to only those required, authorized, and approved to conduct official business or to address authorized quality of life issues.