Adversaries may perform a program download to transfer a user program to a controller.
Variations of program download, such as online edit and program append, allow a controller to continue running during the transfer and reconfiguration process without interruption to process control. However, before starting a full program download (i.e., download all) a controller may need to go into a stop state. This can have negative consequences on the physical process, especially if the controller is not able to fulfill a time-sensitive action. Adversaries may choose to avoid a download all in favor of an online edit or program append to avoid disrupting the physical process. An adversary may need to use the technique Detect Operating Mode or Change Operating Mode to make sure the controller is in the proper mode to accept a program download.
The granularity of control to transfer a user program in whole or parts is dictated by the management protocol (e.g., S7CommPlus, TriStation) and underlying controller API. Thus, program download is a high-level term for the suite of vendor-specific API calls used to configure a controllers user program memory space.
Authenticate all access to field controllers before authorizing access to, or modification of, a device's state, logic, or programs. Centralized authentication techniques can help manage the large number of field controller accounts needed across the ICS.
Provide the ability to verify the integrity of control logic or programs loaded on a controller. While techniques like CRCs and checksums are commonly used, they are not cryptographically strong and can be vulnerable to collisions. Preferably cryptographic hash functions (e.g., SHA-2, SHA-3) should be used. 
All field controllers should restrict the modification of programs to only certain users (e.g., engineers, field technician), preferably through implementing a role-based access mechanism.
Utilize code signatures to verify the integrity of the installed program on safety or control assets has not been changed.
Protocols used for device management should authenticate all network messages to prevent unauthorized system changes.
|M0937||Filter Network Traffic||
Filter for protocols and payloads associated with program download activity to prevent unauthorized device configurations.
|M0804||Human User Authentication||
All field controllers should require users to authenticate for all remote or local management sessions. The authentication mechanisms should also support Account Use Policies, Password Policies, and User Account Management.
Use host-based allowlists to prevent devices from accepting connections from unauthorized systems. For example, allowlists can be used to ensure devices can only connect with master stations or known management/engineering workstations. 
Segment operational network and systems to restrict access to critical system functions to predetermined management systems. 
|M0813||Software Process and Device Authentication||
Authenticate connections from software and devices to prevent unauthorized systems from accessing protected management functions.
|ID||Data Source||Data Component||Detects|
|DS0015||Application Log||Application Log Content||
Monitor devices configuration logs which may contain alerts that indicate whether a program download has occurred. Devices may maintain application logs that indicate whether a full program download, online edit, or program append function has occurred.
Consult asset management systems to understand expected program versions.
|DS0029||Network Traffic||Network Traffic Content||
Monitor for protocol functions related to program download or modification. Program downloads may be observable in ICS automation protocols and remote management protocols.
|DS0040||Operational Databases||Device Alarm||
Monitor device alarms for program downloads, although not all devices produce such alarms.