T1556.004 - Network Device Authentication

Adversaries may use Patch System Image to hard code a password in the operating system, thus bypassing of native authentication mechanisms for local accounts on network devices.

Modify System Image may include implanted code to the operating system for network devices to provide access for adversaries using a specific password. The modification includes a specific password which is implanted in the operating system image via the patch. Upon authentication attempts, the inserted code will first check to see if the user input is the password. If so, access is granted. Otherwise, the implanted code will pass the credentials on for verification of potentially valid credentials.(Citation: Mandiant - Synful Knock)

Atomic Tests:

Currently, no tests are available for this technique.

Detection

Consider verifying the checksum of the operating system file and verifying the image of the operating system in memory.(Citation: Cisco IOS Software Integrity Assurance - Image File Verification)(Citation: Cisco IOS Software Integrity Assurance - Run-Time Memory Verification)

Detection of this behavior may be difficult, detection efforts may be focused on closely related adversary behaviors, such as Modify System Image.