Subvert Trust Controls

Adversaries may undermine security controls that will either warn users of untrusted activity or prevent execution of untrusted programs. Operating systems and security products may contain mechanisms to identify programs or websites as possessing some level of trust. Examples of such features would include a program being allowed to run because it is signed by a valid code signing certificate, a program prompting the user with a warning because it has an attribute set from being downloaded from the Internet, or getting an indication that you are about to connect to an untrusted site.

Adversaries may attempt to subvert these trust mechanisms. The method adversaries use will depend on the specific mechanism they seek to subvert. Adversaries may conduct File and Directory Permissions Modification or Modify Registry in support of subverting these controls.[1] Adversaries may also create or steal code signing certificates to acquire trust on target systems.[2][3]

ID: T1553
Sub-techniques:  T1553.001, T1553.002, T1553.003, T1553.004
Tactic: Defense Evasion
Platforms: Linux, Windows, macOS
Data Sources: API monitoring, Application logs, Binary file metadata, DLL monitoring, File monitoring, Loaded DLLs, Process command-line parameters, Process monitoring, Windows Registry, Windows event logs
Defense Bypassed: Anti-virus, Application control, Autoruns Analysis, Digital Certificate Validation, Process whitelisting, User Mode Signature Validation, Windows User Account Control
Version: 1.0
Created: 05 February 2020
Last Modified: 20 June 2020

Mitigations

Mitigation Description
Execution Prevention

System settings can prevent applications from running that haven't been downloaded through the Apple Store (or other legitimate repositories) which can help mitigate some of these issues. Also enable application control solutions such as AppLocker and/or Device Guard to block the loading of malicious content.

Operating System Configuration

Windows Group Policy can be used to manage root certificates and the Flags value of HKLM\SOFTWARE\Policies\Microsoft\SystemCertificates\Root\ProtectedRoots can be set to 1 to prevent non-administrator users from making further root installations into their own HKCU certificate store. [4]

Restrict Registry Permissions

Ensure proper permissions are set for Registry hives to prevent users from modifying keys related to SIP and trust provider components. Components may still be able to be hijacked to suitable functions already present on disk if malicious modifications to Registry keys are not prevented.

Software Configuration

HTTP Public Key Pinning (HPKP) is one method to mitigate potential man-in-the-middle situations where and adversary uses a mis-issued or fraudulent certificate to intercept encrypted communications by enforcing use of an expected certificate. [5]

Detection

Collect and analyze signing certificate metadata on software that executes within the environment to look for unusual certificate characteristics and outliers. Periodically baseline registered SIPs and trust providers (Registry entries and files on disk), specifically looking for new, modified, or non-Microsoft entries. [1] A system's root certificates are unlikely to change frequently. Monitor new certificates installed on a system that could be due to malicious activity.[4]

Analyze Autoruns data for oddities and anomalies, specifically malicious files attempting persistent execution by hiding within auto-starting locations. Autoruns will hide entries signed by Microsoft or Windows by default, so ensure "Hide Microsoft Entries" and "Hide Windows Entries" are both deselected.[1]

Monitor and investigate attempts to modify extended file attributes with utilities such as xattr. Built-in system utilities may generate high false positive alerts, so compare against baseline knowledge for how systems are typically used and correlate modification events with other indications of malicious activity where possible.

References