T1222 - File and Directory Permissions Modification

Adversaries may modify file or directory permissions/attributes to evade access control lists (ACLs) and access protected files.(Citation: Hybrid Analysis Icacls1 June 2018)(Citation: Hybrid Analysis Icacls2 May 2018) 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.).

Modifications may include changing specific access rights, which may require taking ownership of a file or directory and/or elevated permissions depending on the file or directory’s existing permissions. This may enable malicious activity such as modifying, replacing, or deleting specific files or directories. 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, Unix Shell Configuration Modification, or tainting/hijacking other instrumental binary/configuration files via Hijack Execution Flow.

Adversaries may also change permissions of symbolic links. For example, malware (particularly ransomware) may modify symbolic links and associated settings to enable access to files from local shortcuts with remote paths.(Citation: new_rust_based_ransomware)(Citation: bad_luck_blackcat)(Citation: falconoverwatch_blackcat_attack)(Citation: blackmatter_blackcat)(Citation: fsutil_behavior)

Atomic Tests:

Currently, no tests are available for this technique.

Detection

Monitor and investigate attempts to modify ACLs and file/directory ownership. Many of the commands used to modify ACLs 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.(Citation: EventTracker File Permissions Feb 2014)

Shield Active Defense

Pocket Litter

Place data on a system to reinforce the legitimacy of the system or user.

Pocket Litter is data placed on a system to convince an adversary that the system and users are real. Pocket litter includes documents, registry entries, log history, browsing history, connection history, and other user data that one would expect to exist on a user’s computer. This content may overlap with Decoy Content, however Pocket Litter covers aspects beyond just content (e.g.: Installed Applications, source code, clutter on a system, etc.).

Opportunity

In an adversary engagement scenario, there is an opportunity to seed content to influence an adversary’s behaviors, test their interest in specific topics, or add legitimacy to a system or environment.

Use Case

A defender can seed content interesting files to an adversary, but lock the permissions down. The goal would be to force the adversary to expose their TTPs for circumventing the restrictions.

Procedures

When staging a decoy system and user account, populate a user’s folders and web history to make it look realistic to an adversary. Stage a USB device with documents on a specific topic in order to see if they are exfiltrated by an adversary.