Technique on mitre.org

T1222.001: Windows File and Directory Permissions Modification

Adversaries may modify file or directory permissions/attributes to evade access control lists (ACLs) and access protected files. File and directory permissions are commonly managed by ACLs configured by the file or directory owner, or users with the appropriate permissions. File and directory ACL implementations vary by platform, but generally explicitly designate which users or groups can perform which actions (read, write, execute, etc.).

Windows implements file and directory ACLs as Discretionary Access Control Lists (DACLs). Similar to a standard ACL, DACLs identifies the accounts that are allowed or denied access to a securable object. When an attempt is made to access a securable object, the system checks the access control entries in the DACL in order. If a matching entry is found, access to the object is granted. Otherwise, access is denied.

Adversaries can interact with the DACLs using built-in Windows commands, such as icacls, cacls, takeown, and attrib, which can grant adversaries higher permissions on specific files and folders. Further, PowerShell provides cmdlets that can be used to retrieve or modify file and directory DACLs. Specific file and directory modifications may be a required step for many techniques, such as establishing Persistence via Accessibility Features, Boot or Logon Initialization Scripts, or tainting/hijacking other instrumental binary/configuration files via Hijack Execution Flow.

Positive Technologies products that cover the technique

MaxPatrol SIEM knowledge base

active_directory_attacks: PT-CR-1342: Subrule_PowerView_Objects_Actions: Remote change of domain objects (domain users and groups, machine accounts) using the PowerView tool (PowerViewPy) is detected active_directory_attacks: PT-CR-1344: Remote_Actions_With_Domain_Objects: A PowerView script was used. Attackers use the PowerView tool for reconnaissance in Windows domains.

Detection

ID	DS0009	Data source and component	Process: Process Creation	Description	Monitor for newly constructed processes and/or command-lines that can interact with the DACLs using built-in Windows commands, such as icacls, cacls, takeown, and attrib, which can grant adversaries higher permissions on specific files and folders.

ID	DS0022	Data source and component	File: File Metadata	Description	Consider enabling file/directory permission change auditing on folders containing key binary/configuration files. For example, Windows Security Log events (Event ID 4670) are created when DACLs are modified. Adversaries sometimes modify object access rights at the operating system level. There are varying motivations behind this action - they may not want some files/objects to be changed on systems for persistence reasons and therefore provide admin only rights; also, they may want files to be accessible with lower levels of permissions. Windows environment logs can be noisy, so we take the following into consideration: We need to exclude events generated by the local system (subject security ID “NT AUTHORITY\SYSTEM”) and focus on actual user events. When a permission modification is made for a folder, a new event log is generated for each subfolder and file under that folder. It is advised to group logs based on handle ID or user ID. The Windows security log (event ID 4670) also includes information about the process that modifies the file permissions. It is advised to focus on uncommon process names, and it is also uncommon for real-users to perform this task without a GUI. Pseudocode Event ID is for Windows Security Log (Event ID 4670 - Permissions on an object were changed). Windows Event ID 4719 (An Attempt Was Made to Access An Object) can also be used to alert on changes to Active Directory audit policy for a system. Analytic 1 - Access Permission Modification for Windows `(source="*WinEventLog:Security" EventCode IN (4670, 4719)) Object_Type="File" Security_ID!="NT AUTHORITY\SYSTEM"`

ID	DS0017	Data source and component	Command: Command Execution	Description	Monitor for executed commands and arguments for PowerShell cmdlets that can be used to retrieve or modify file and directory DACLs.

ID	DS0026	Data source and component	Active Directory: Active Directory Object Modification	Description	Monitor for changes made to DACLs and file/directory ownership. Many of the commands used to modify DACLs and file/directory ownership are built-in system utilities and may generate a high false positive alert rate, so compare against baseline knowledge for how systems are typically used and correlate modification events with other indications of malicious activity where possible.

ID	Data source and component	Description
DS0009	Process: Process Creation	Monitor for newly constructed processes and/or command-lines that can interact with the DACLs using built-in Windows commands, such as icacls, cacls, takeown, and attrib, which can grant adversaries higher permissions on specific files and folders.
DS0022	File: File Metadata	Consider enabling file/directory permission change auditing on folders containing key binary/configuration files. For example, Windows Security Log events (Event ID 4670) are created when DACLs are modified. Adversaries sometimes modify object access rights at the operating system level. There are varying motivations behind this action - they may not want some files/objects to be changed on systems for persistence reasons and therefore provide admin only rights; also, they may want files to be accessible with lower levels of permissions. Windows environment logs can be noisy, so we take the following into consideration: We need to exclude events generated by the local system (subject security ID “NT AUTHORITY\SYSTEM”) and focus on actual user events. When a permission modification is made for a folder, a new event log is generated for each subfolder and file under that folder. It is advised to group logs based on handle ID or user ID. The Windows security log (event ID 4670) also includes information about the process that modifies the file permissions. It is advised to focus on uncommon process names, and it is also uncommon for real-users to perform this task without a GUI. Pseudocode Event ID is for Windows Security Log (Event ID 4670 - Permissions on an object were changed). Windows Event ID 4719 (An Attempt Was Made to Access An Object) can also be used to alert on changes to Active Directory audit policy for a system. Analytic 1 - Access Permission Modification for Windows `(source="*WinEventLog:Security" EventCode IN (4670, 4719)) Object_Type="File" Security_ID!="NT AUTHORITY\SYSTEM"`
DS0017	Command: Command Execution	Monitor for executed commands and arguments for PowerShell cmdlets that can be used to retrieve or modify file and directory DACLs.
DS0026	Active Directory: Active Directory Object Modification	Monitor for changes made to DACLs and file/directory ownership. Many of the commands used to modify DACLs and file/directory ownership are built-in system utilities and may generate a high false positive alert rate, so compare against baseline knowledge for how systems are typically used and correlate modification events with other indications of malicious activity where possible.

Mitigation

ID	M1026	Name	Privileged Account Management	Description	Ensure critical system files as well as those known to be abused by adversaries have restrictive permissions and are owned by an appropriately privileged account, especially if access is not required by users nor will inhibit system functionality.

ID	M1022	Name	Restrict File and Directory Permissions	Description	Applying more restrictive permissions to files and directories could prevent adversaries from modifying the access control lists.

ID	Name	Description
M1026	Privileged Account Management	Ensure critical system files as well as those known to be abused by adversaries have restrictive permissions and are owned by an appropriately privileged account, especially if access is not required by users nor will inhibit system functionality.
M1022	Restrict File and Directory Permissions	Applying more restrictive permissions to files and directories could prevent adversaries from modifying the access control lists.