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File and Directory Permissions Modification: Linux and Mac 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.).

Most Linux and Linux-based platforms provide a standard set of permission groups (user, group, and other) and a standard set of permissions (read, write, and execute) that are applied to each group. While nuances of each platform’s permissions implementation may vary, most of the platforms provide two primary commands used to manipulate file and directory ACLs: chown (short for change owner), and chmod (short for change mode).

Adversarial may use these commands to make themselves the owner of files and directories or change the mode if current permissions allow it. They could subsequently lock others out of the file. Specific file and directory modifications may be a required step for many techniques, such as establishing Persistence via Unix Shell Configuration Modification or tainting/hijacking other instrumental binary/configuration files via Hijack Execution Flow.[3]

ID: T1222.002
Sub-technique of:  T1222
ⓘ
Tactic: Defense Evasion
ⓘ
Platforms: Linux, macOS
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Permissions Required: User, root
Version: 1.1
Created: 04 February 2020
Last Modified: 13 September 2021

Procedure Examples

ID Name Description
G0050 APT32

APT32's macOS backdoor changes the permission of the file it wants to execute to 755.[4]
S0482 Bundlore

Bundlore changes the permissions of a payload using the command chmod -R 755.[3]
S0281 Dok

Dok gives all users execute permissions for the application using the command chmot +x /Users/Shared/AppStore.app.[5]
S0599 Kinsing

Kinsing has used chmod to modify permissions on key files for use.[6]
S0402 OSX/Shlayer

OSX/Shlayer can use the chmod utility to set a file as executable, such as chmod 777 or chmod +x.[3][7][8]
S0352 OSX_OCEANLOTUS.D

OSX_OCEANLOTUS.D has changed permissions of a second-stage payload to an executable via chmod.[9]
S0598 P.A.S. Webshell

P.A.S. Webshell has the ability to modify file permissions.[10]
S0587 Penquin

Penquin can add the executable flag to a downloaded file.[11]
G0106 Rocke

Rocke has changed file permissions of files so they could not be modified.[12]

G0139 TeamTNT

TeamTNT has modified the permissions on binaries with chattr.[13]
S0658 XCSSET

XCSSET uses the chmod +x command to grant executable permissions to the malicious file.[3]

Mitigations

ID Mitigation 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.

Detection

ID Data Source Data Component
DS0017 Command Command Execution
DS0022 File File Metadata
DS0009 Process Process Creation

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. Commonly abused command arguments include chmod +x, chmod -R 755, and chmod 777.[3]

Consider enabling file/directory permission change auditing on folders containing key binary/configuration files.

References

  1. Hybrid Analysis. (2018, June 12). c9b65b764985dfd7a11d3faf599c56b8.exe. Retrieved August 19, 2018.
  2. Hybrid Analysis. (2018, May 30). 2a8efbfadd798f6111340f7c1c956bee.dll. Retrieved August 19, 2018.
  3. Phil Stokes. (2021, February 16). 20 Common Tools & Techniques Used by macOS Threat Actors & Malware. Retrieved August 23, 2021.
  4. Dumont, R.. (2019, April 9). OceanLotus: macOS malware update. Retrieved April 15, 2019.
  5. Ofer Caspi. (2017, May 4). OSX Malware is Catching Up, and it wants to Read Your HTTPS Traffic. Retrieved October 5, 2021.
  6. Singer, G. (2020, April 3). Threat Alert: Kinsing Malware Attacks Targeting Container Environments. Retrieved April 1, 2021.
  7. Carbon Black Threat Analysis Unit. (2019, February 12). New macOS Malware Variant of Shlayer (OSX) Discovered. Retrieved August 8, 2019.
  1. Jaron Bradley. (2021, April 26). Shlayer malware abusing Gatekeeper bypass on macOS. Retrieved September 22, 2021.
  2. Phil Stokes. (2020, December 2). APT32 Multi-stage macOS Trojan Innovates on Crimeware Scripting Technique. Retrieved September 13, 2021.
  3. ANSSI. (2021, January 27). SANDWORM INTRUSION SET CAMPAIGN TARGETING CENTREON SYSTEMS. Retrieved March 30, 2021.
  4. Leonardo. (2020, May 29). MALWARE TECHNICAL INSIGHT TURLA “Penquin_x64”. Retrieved March 11, 2021.
  5. Anomali Labs. (2019, March 15). Rocke Evolves Its Arsenal With a New Malware Family Written in Golang. Retrieved April 24, 2019.
  6. Fiser, D. Oliveira, A. (n.d.). Tracking the Activities of TeamTNT A Closer Look at a Cloud-Focused Malicious Actor Group. Retrieved September 22, 2021.