cyberstrikeus Ensure /dev/shm is configured
Description
/dev/shm is a traditional shared memory concept. One program will create a memory portion, which other processes (if permitted) can access. Mounting tmpfs at /dev/shm is handled automatically by systemd.
Rationale
Any user can upload and execute files inside the /dev/shm similar to the /tmp partition. Configuring /dev/shm allows an administrator to set the noexec option on the mount, making /dev/shm useless for an attacker to install executable code. It would also prevent an attacker from establishing a hardlink to a system setuid program and wait for it to be updated. Once the program was updated, the hardlink would be broken and the attacker would have his own copy of the program. If the program happened to have a security vulnerability, the attacker could continue to exploit the known flaw.
Impact
None noted.
Audit Procedure
Command Line
# Run the following command and verify output shows /dev/shm is mounted:
findmnt /dev/shm
Expected Result
TARGET SOURCE FSTYPE OPTIONS
/dev/shm tmpfs tmpfs rw,nosuid,nodev,noexec
Remediation
Command Line
# Edit /etc/fstab and add or edit the following line:
# tmpfs /dev/shm tmpfs defaults,noexec,nodev,nosuid,seclabel 0 0
# Run the following command to remount /dev/shm:
mount -o remount,noexec,nodev,nosuid /dev/shm
Default Value
By default /dev/shm is mounted automatically by systemd.
References
- CIS Controls Version 7 - 5.1 Establish Secure Configurations: Maintain documented, standard security configuration standards for all authorized operating systems and software.
- CIS Controls Version 7 - 13 Data Protection.
Profile
Level 1 - Server / Level 1 - Workstation, Assessment: Automated