Container-Optimized OS
TMA-COS-5.3.4
Ensure default user umask is 027 or more restrictive
Description
The default umask determines the permissions of files created by users. The user creating the file has the discretion of making their files and directories readable by others via the chmod command. Users who wish to allow their files and directories to be readable by others by default may choose a different default umask by inserting the umask command into the standard shell configuration files ( .profile , .bashrc , etc.) in their home directories. Setting a very secure default value for umask ensures that users make a conscious choice about their file permissions. A default umask setting of 077 causes files and directories created by users to not be readable by any other user on the system. A umask of 027 would make files and directories readable by users in the same Unix group, while a umask of 022 would make files readable by every user on the system.
How it is checked
Audit method: Shell command
ok=0; grep -Eiq "^\s*UMASK\s+(0[0-7][2-7]7|[0-7][2-7]7)\b" /etc/login.defs 2>/dev/null && ok=1; grep -REiq "^\s*umask\s+(0[0-7][2-7]7|[0-7][2-7]7)\b" /etc/profile /etc/profile.d /etc/bashrc 2>/dev/null && ok=1; bad=$(grep -RPih "(^|^[^#]*)\s*umask\s+([0-7][0-7][01][0-7]\b|[0-7][0-7][0-7][0-6]\b|[0-7][01][0-7]\b|[0-7][0-7][0-6]\b)" /etc/login.defs /etc/profile /etc/profile.d /etc/bashrc 2>/dev/null); [ $ok -eq 1 ] && [ -z "$bad" ] && echo compliant || echo noncompliant- Expected output
compliant
How it is fixed
Fix method: Guidance or infrastructure patch
Edit the /etc/bash/bashrc, /etc/profile and /etc/profile.d/*.sh files (and the appropriate files for any other shell supported on your system) and add or edit any umask parameters as follows: umask 027
Properties
- Operating systems
- Any
- Tags
- container-optimized-oscos
- Reference
- CIS Google Container-Optimized OS Benchmark v1.2.0 - 5.3.4 Ensure default user umask is 027 or more restrictive
Check this host
Run this on a machine you are allowed to audit. The scan is read-only.
tmaegis scan --target cos --level 2