When the setuid or setgid bits are set on Linux or macOS for an application, this means that the application will run with the privileges of the owning user or group respectively [1]. Normally an application is run in the current user’s context, regardless of which user or group owns the application. There are instances where programs need to be executed in an elevated context to function properly, but the user running them doesn’t need the elevated 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. These bits are indicated with an “s” instead of an “x” when viewing a file’s attributes via ls -l. The chmod program can set these bits with via bitmasking, chmod 4777 [file] or via shorthand naming, chmod u+s [file].
An adversary can take advantage of this to either do a shell escape or exploit a vulnerability in an application with the setsuid or setgid bits to get code running in a different user’s context. Additionally, adversaries can use this mechanism on their own malware to make sure they’re able to execute in elevated contexts in the future [2].
name: Linux.Sys.SUID
description: |
When the setuid or setgid bits are set on Linux or macOS for an
application, this means that the application will run with the
privileges of the owning user or group respectively [1]. Normally an
application is run in the current user’s context, regardless of
which user or group owns the application. There are instances where
programs need to be executed in an elevated context to function
properly, but the user running them doesn’t need the elevated
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. These bits are indicated with
an "s" instead of an "x" when viewing a file's attributes via ls
-l. The chmod program can set these bits with via bitmasking, chmod
4777 [file] or via shorthand naming, chmod u+s [file].
An adversary can take advantage of this to either do a shell escape
or exploit a vulnerability in an application with the setsuid or
setgid bits to get code running in a different user’s
context. Additionally, adversaries can use this mechanism on their
own malware to make sure they're able to execute in elevated
contexts in the future [2].
reference:
- https://attack.mitre.org/techniques/T1166/
parameters:
- name: GlobExpression
default: /usr/**
sources:
- query: |
SELECT Mode.String AS Mode,
OSPath, Size,
Mtime,
Sys.Uid AS OwnerID,
Sys.Gid AS GroupID
FROM glob(globs=GlobExpression) WHERE Mode =~ '^g|u'