Abuse Elevation Control Mechanism: Setuid and Setgid
Other sub-techniques of Abuse Elevation Control Mechanism (6)
An adversary may abuse configurations where an application has the setuid or setgid bits set in order to get code running in a different (and possibly more privileged) user’s context. On Linux or macOS, when the setuid or setgid bits are set for an application binary, the application will run with the privileges of the owning user or group respectively.(Citation: setuid man page) Normally an application is run in the current user’s context, regardless of which user or group owns the application. However, there are instances where programs need to be executed in an elevated context to function properly, but the user running them may not have the specific required privileges.
Instead of creating an entry in the sudoers file, which must be done by root, any user can specify the setuid or setgid flag to be set for their own applications (i.e. Linux and Mac File and Directory Permissions Modification). The chmod command can set these bits with bitmasking, chmod 4777 [file] or via shorthand naming, chmod u+s [file]. This will enable the setuid bit. To enable the setgid bit, chmod 2775 and chmod g+s can be used.
Adversaries can use this mechanism on their own malware to make sure they're able to execute in elevated contexts in the future.(Citation: OSX Keydnap malware) This abuse is often part of a "shell escape" or other actions to bypass an execution environment with restricted permissions.
Alternatively, adversaries may choose to find and target vulnerable binaries with the setuid or setgid bits already enabled (i.e. File and Directory Discovery). The setuid and setguid bits are indicated with an "s" instead of an "x" when viewing a file's attributes via ls -l. The find command can also be used to search for such files. For example, find / -perm +4000 2>/dev/null can be used to find files with setuid set and find / -perm +2000 2>/dev/null may be used for setgid. Binaries that have these bits set may then be abused by adversaries.(Citation: GTFOBins Suid)
Procedure Examples |
|
| Name | Description |
|---|---|
| Keydnap |
Keydnap adds the setuid flag to a binary so it can easily elevate in the future.(Citation: OSX Keydnap malware) |
| Exaramel for Linux |
Exaramel for Linux can execute commands with high privileges via a specific binary with setuid functionality.(Citation: ANSSI Sandworm January 2021) |
Mitigations |
|
| Mitigation | Description |
|---|---|
| Operating System Configuration |
Operating System Configuration involves adjusting system settings and hardening the default configurations of an operating system (OS) to mitigate adversary exploitation and prevent abuse of system functionality. Proper OS configurations address security vulnerabilities, limit attack surfaces, and ensure robust defense against a wide range of techniques. This mitigation can be implemented through the following measures: Disable Unused Features: - Turn off SMBv1, LLMNR, and NetBIOS where not needed. - Disable remote registry and unnecessary services. Enforce OS-level Protections: - Enable Data Execution Prevention (DEP), Address Space Layout Randomization (ASLR), and Control Flow Guard (CFG) on Windows. - Use AppArmor or SELinux on Linux for mandatory access controls. Secure Access Settings: - Enable User Account Control (UAC) for Windows. - Restrict root/sudo access on Linux/macOS and enforce strong permissions using sudoers files. File System Hardening: - Implement least-privilege access for critical files and system directories. - Audit permissions regularly using tools like icacls (Windows) or getfacl/chmod (Linux/macOS). Secure Remote Access: - Restrict RDP, SSH, and VNC to authorized IPs using firewall rules. - Enable NLA for RDP and enforce strong password/lockout policies. Harden Boot Configurations: - Enable Secure Boot and enforce UEFI/BIOS password protection. - Use BitLocker or LUKS to encrypt boot drives. Regular Audits: - Periodically audit OS configurations using tools like CIS Benchmarks or SCAP tools. *Tools for Implementation* Windows: - Microsoft Group Policy Objects (GPO): Centrally enforce OS security settings. - Windows Defender Exploit Guard: Built-in OS protection against exploits. - CIS-CAT Pro: Audit Windows security configurations based on CIS Benchmarks. Linux/macOS: - AppArmor/SELinux: Enforce mandatory access controls. - Lynis: Perform comprehensive security audits. - SCAP Security Guide: Automate configuration hardening using Security Content Automation Protocol. Cross-Platform: - Ansible or Chef/Puppet: Automate configuration hardening at scale. - OpenSCAP: Perform compliance and configuration checks. |
Detection
Monitor the file system for files that have the setuid or setgid bits set. Monitor for execution of utilities, like chmod, and their command-line arguments to look for setuid or setguid bits being set.
References
- Michael Kerrisk. (2017, September 15). Linux Programmer's Manual. Retrieved September 21, 2018.
- Marc-Etienne M.Leveille. (2016, July 6). New OSX/Keydnap malware is hungry for credentials. Retrieved July 3, 2017.
- Emilio Pinna, Andrea Cardaci. (n.d.). GTFOBins. Retrieved January 28, 2022.
- ANSSI. (2021, January 27). SANDWORM INTRUSION SET CAMPAIGN TARGETING CENTREON SYSTEMS. Retrieved March 30, 2021.
Связанные риски
Каталоги
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