Linux and Mac Permissions
Where this stands
One published detection covers this technique. Every one is unverified — no rule on Siemphony has been executed against real telemetry.
What the technique is
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.). 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.
Read it on attack.mitre.orgWhat MITRE says you would watch
- AN0998
Linux permission escalation behavioral chain: (1) Process creation of permission modification utilities (chmod, chown, chgrp, setfacl) with suspicious parameters indicating privilege escalation intent, (2) System call analysis revealing direct file metadata manipulation (chmod, fchmod, chown, fchown syscalls), (3) Extended attribute and ACL modifications targeting critical system paths, (4) Temporal correlation with subsequent file access or process execution from modified locations, (5) Anomalous permission patterns deviating from system baselines
- AN0999
macOS permission and attribute manipulation behavioral chain: (1) Process execution of permission utilities (chmod, chown, chgrp) or macOS-specific tools (chflags) with suspicious parameters, (2) System Integrity Protection (SIP) bypass attempts through permission modifications, (3) File flags manipulation (uchg, schg, hidden) for evasion or persistence, (4) Extended attribute (xattr) modifications affecting security metadata, (5) Unified log correlation with file system events and subsequent access patterns, (6) Gatekeeper and code signing bypass through permission/attribute manipulation
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