Abuse Elevation Control Mechanism: Setuid и Setgid
Other sub-techniques of Abuse Elevation Control Mechanism (4)
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 setgit 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)
Примеры процедур |
|
Название | Описание |
---|---|
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) |
Контрмеры |
|
Контрмера | Описание |
---|---|
Operating System Configuration |
Make configuration changes related to the operating system or a common feature of the operating system that result in system hardening against techniques. |
Обнаружение
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.
Ссылки
- 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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