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.^[1],[2],[3] 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.^[4]

References

1. Microsoft. (n.d.). Change which programs Windows 7 uses by default. Retrieved July 26, 2016.
2. Microsoft. (n.d.). Specifying File Handlers for File Name Extensions. Retrieved September 12, 2024.
3. Plett, C. et al.. (2017, October 15). assoc. Retrieved August 7, 2018.
4. Sioting, S. (2012, October 8). TROJ_FAKEAV.GZD. Retrieved August 8, 2018.

Tichete legate

• MITREATTACK -

  © 2026 The MITRE Corporation. This work is reproduced and distributed with the permission of The MITRE Corporation. https://attack.mitre.org/

  Terms of Use

  LICENSE

  The MITRE Corporation (MITRE) hereby grants you a non-exclusive, royalty-free license to use ATT&CK^® for research, development, and commercial purposes. Any copy you make for such purposes is authorized provided that you reproduce MITRE's copyright designation and this license in any such copy.

  "© 2026 The MITRE Corporation. This work is reproduced and distributed with the permission of The MITRE Corporation."

  DISCLAIMERS

  MITRE does not claim ATT&CK enumerates all possibilities for the types of actions and behaviors documented as part of its adversary model and framework of techniques. Using the information contained within ATT&CK to address or cover full categories of techniques will not guarantee full defensive coverage as there may be undisclosed techniques or variations on existing techniques not documented by ATT&CK.

  ALL DOCUMENTS AND THE INFORMATION CONTAINED THEREIN ARE PROVIDED ON AN "AS IS" BASIS AND THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE MITRE CORPORATION, ITS BOARD OF TRUSTEES, OFFICERS, AGENTS, AND EMPLOYEES, DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION THEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

  See our FAQ for more information on how to use and represent the ATT&CK name.