Adversaries may modify or add a program on a controller to affect how it interacts with the physical process, peripheral devices and other hosts on the network. Modification to controller programs can be accomplished using a Program Download in addition to other types of program modification such as online edit and program append.
Program modification encompasses the addition and modification of instructions and logic contained in Program Organization Units (POU) [1] and similar programming elements found on controllers. This can include, for example, adding new functions to a controller, modifying the logic in existing functions and making new calls from one function to another.
Some programs may allow an adversary to interact directly with the native API of the controller to take advantage of obscure features or vulnerabilities.
| ID | Name | Description |
|---|---|---|
| S1006 | PLC-Blaster |
PLC-Blaster copies itself to various Program Organization Units (POU) on the target device. The POUs include the Data Block, Function, and Function Block. [2] |
| S0603 | Stuxnet |
Stuxnet infects PLCs with different code depending on the characteristics of the target system. An infection sequence consists of code blocks and data blocks that will be downloaded to the PLC to alter its behavior. [3] |
| ID | Asset |
|---|---|
| A0003 | Programmable Logic Controller (PLC) |
| A0010 | Safety Controller |
| ID | Mitigation | Description |
|---|---|---|
| M0947 | Audit |
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. [4] |
| M0800 | Authorization Enforcement |
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. |
| M0945 | Code Signing |
Utilize code signatures to verify the integrity and authenticity of programs installed on safety or control assets. |
| 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. |
| ID | Data Source | Data Component | Detects |
|---|---|---|---|
| DS0015 | Application Log | Application Log Content |
Monitor device application logs that indicate the program has changed, although not all devices produce such logs. |
| DS0039 | Asset | Software |
Engineering and asset management software will often maintain a copy of the expected program loaded on a controller and may also record any changes made to controller programs. Data from these platforms can be used to identify modified controller programs. |
| DS0029 | Network Traffic | Network Traffic Content |
Monitor device management protocols for functions that modify programs such as online edit and program append events. |
| DS0040 | Operational Databases | Device Alarm |
Monitor device alarms that indicate the program has changed, although not all devices produce such alarms. |