File and Directory Permissions Modification: Windows File and Directory Permissions Modification

ID Name
T1222.001 Windows File and Directory Permissions Modification
T1222.002 Linux and Mac File and Directory Permissions Modification

Adversaries may modify file or directory permissions/attributes to evade access control lists (ACLs) and access protected files.[1][2] 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).[3] 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.[4]

Adversaries can interact with the DACLs using built-in Windows commands, such as icacls, 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.

ID: T1222.001
Sub-technique of:  T1222
Tactic: Defense Evasion
Platforms: Windows
Permissions Required: Administrator, SYSTEM, User
Data Sources: File monitoring, Process command-line parameters, Process monitoring, Windows event logs
Version: 1.0
Created: 04 February 2020
Last Modified: 29 March 2020

Procedure Examples

Name Description
JPIN

JPIN can use the command-line utility cacls.exe to change file permissions.[5]

WannaCry

WannaCry uses attrib +h and icacls . /grant Everyone:F /T /C /Q to make some of its files hidden and grant all users full access controls.[6]

Mitigations

Mitigation Description
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.

Restrict File and Directory Permissions

Applying more restrictive permissions to files and directories could prevent adversaries from modifying the access control lists.

Detection

Monitor and investigate attempts to modify 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.

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.[7]

References