cyberstrikeus 1.7.7 Ensure GDM disabling automatic mounting of removable media is not overridden (Automated)
Profile
- Level 1 - Server
- Level 2 - Workstation
Description
By default GNOME automatically mounts removable media when inserted as a convenience to the user.
By using the lockdown mode in dconf, you can prevent users from changing specific settings. To lock down a dconf key or subpath, create a locks subdirectory in the keyfile directory. The files inside this directory contain a list of keys or subpaths to lock. Just as with the keyfiles, you may add any number of files to this directory.
Rationale
With automounting enabled anyone with physical access could attach a USB drive or disc and have its contents available in system even if they lacked permissions to mount it themselves.
Impact
The use of portable hard drives is very common for workstation users.
Audit Procedure
Command Line
Run the following command to verify automount=false and automount-open=false is correctly configured to ensure automatic mounting of removable media is not overridden:
# grep -Psi "automount" /etc/dconf/db/*/locks/*
/etc/dconf/db/local.d/locks/00-media-automount:automount=false
/etc/dconf/db/local.d/locks/00-media-automount:automount-open=false
Expected Result
Lock entries for automount and automount-open should be present.
Remediation
Command Line
- To prevent the user from overriding these settings, create the file
/etc/dconf/db/local.d/locks/00-media-automountwith the following content:
[org/gnome/desktop/media-handling]
automount=false
automount-open=false
- Update the systems databases:
# dconf update
Note:
- A user profile must exist in order to apply locks. If a user profile does not exist review the remediation steps in the previous recommendation.
- Users must log out and back in again before the system-wide settings take effect.
References
- https://help.gnome.org/admin/system-admin-guide/stable/dconf-lockdown.html.en
- NIST SP 800-53 Rev. 5: CM-1, CM-2, CM-6, CM-7, IA-5
- https://manpages.ubuntu.com/manpages/trusty/man1/gsettings.1.html
- https://access.redhat.com/solutions/20107
MITRE ATT&CK Mappings: T1091, T1091.000 | TA0001, TA0008 | M1042