T1546.001 Change Default File Association

Technique

T1546.001

Tactics

Privilege Escalation, Persistence

Research, 90 days

1

KEV CVEs mapped

0

SigmaHQ rules

5

Elastic, Splunk

2

thrunt rules

0

Upstream

https://attack.mitre.org/techniques/T1546/001

MITRE 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.(Citation: Microsoft Change Default Programs)(Citation: Microsoft File Handlers)(Citation: Microsoft Assoc Oct 2017) 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 <code>HKEY_CLASSES_ROOT\.[extension]</code>, for example <code>HKEY_CLASSES_ROOT\.txt</code>. The entries point to a handler for that extension located at <code>HKEY_CLASSES_ROOT\\[handler]</code>. The various commands are then listed as subkeys underneath the shell key at <code>HKEY_CLASSES_ROOT\\[handler]\shell\\[action]\command</code>. For example: * <code>HKEY_CLASSES_ROOT\txtfile\shell\open\command</code> * <code>HKEY_CLASSES_ROOT\txtfile\shell\print\command</code> * <code>HKEY_CLASSES_ROOT\txtfile\shell\printto\command</code> 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.(Citation: TrendMicro TROJ-FAKEAV OCT 2012)

Research citing this technique

Reports and advisories from the last 90 days that cite this technique.

• 2026-10-14 Group-IB: KGB RAT: A Fully Undetectable Windows Trojan Built to Spy, Steal, and Terrorize

Detection coverage

SigmaHQ community rules

• Change Default File Association Via Assoc (core)
• Change Default File Association To Executable Via Assoc (core)
• Registry Modification of MS-settings Protocol Handler (core)
• Shell Open Registry Keys Manipulation (core)
• Suspicious Shell Open Command Registry Modification (core)

Elastic and Splunk rules

• Windows Change File Association Command To Notepad (splunk)
• Windows New Default File Association Value Set (splunk)

Signal counts reflect the current corpus snapshot. Research citations are the technique IDs named in vendor reports and government advisories from the last 90 days; KEV mappings come from MITRE CTID. Coverage is the SigmaHQ rule inventory (core, emerging-threats, threat-hunting) at release r2026-07-01 plus Elastic and Splunk production rules. Rule bodies are not mirrored; links go upstream.