t1546-001-change-default-file-association

name	T1546.001_change-default-file-association
description	Adversaries may establish persistence by executing malicious content triggered by a file type association.
category	authorization
version	18.1
author	cyberstrike-official
tags	["mitre-attack","enterprise","t1546.001","privilege-escalation","persistence","windows","sub-technique"]
technique_id	T1546.001
tactic	privilege-escalation
all_tactics	["privilege-escalation","persistence"]
platforms	["Windows"]
mitre_url	https://attack.mitre.org/techniques/T1546/001
tech_stack	["windows"]
cwe_ids	["CWE-269"]
chains_with	["T1546","T1546.002","T1546.003","T1546.004","T1546.005","T1546.006","T1546.007","T1546.008","T1546.009","T1546.010","T1546.011","T1546.012","T1546.013","T1546.014","T1546.015","T1546.016","T1546.017","T1546.018"]
prerequisites	["T1546"]
severity_boost	{"T1546":"Chain with T1546 for deeper attack path","T1546.002":"Chain with T1546.002 for deeper attack path","T1546.003":"Chain with T1546.003 for deeper attack path"}

T1546.001 Change Default File Association

Sub-technique of: T1546

High-Level Description

Adversaries may establish persistence by executing malicious content triggered by a file type association. When a file is opened, the default program used to open the file (also called the file association or handler) is checked. File association selections are stored in the Windows Registry and can be edited by users, administrators, or programs that have Registry access or by administrators using the built-in assoc utility. Applications can modify the file association for a given file extension to call an arbitrary program when a file with the given extension is opened.

System file associations are listed under HKEY_CLASSES_ROOT.[extension], for example HKEY_CLASSES_ROOT.txt. The entries point to a handler for that extension located at HKEY_CLASSES_ROOT\[handler]. The various commands are then listed as subkeys underneath the shell key at HKEY_CLASSES_ROOT\[handler]\shell\[action]\command. For example:

• HKEY_CLASSES_ROOT\txtfile\shell\open\command
• HKEY_CLASSES_ROOT\txtfile\shell\print\command
• HKEY_CLASSES_ROOT\txtfile\shell\printto\command

The values of the keys listed are commands that are executed when the handler opens the file extension. Adversaries can modify these values to continually execute arbitrary commands.

Kill Chain Phase

• Privilege Escalation (TA0004)
• Persistence (TA0003)

Platforms: Windows

What to Check

• Identify if Change Default File Association technique is applicable to target environment
• Check Windows systems for indicators of Change Default File Association
• Assess detection coverage (1 detection strategies)

How to Test

Atomic Red Team Tests

The following tests are from Atomic Red Team and provide actionable ways to test this technique:

Atomic Test 1: Change Default File Association

Change Default File Association From cmd.exe of hta to notepad.

Upon successful execution, cmd.exe will change the file association of .hta to notepad.exe.

Supported Platforms: windows Elevation Required: Yes