CIS Ubuntu 14.04 LTS - 5.4.4 Ensure default user umask is 027 or more restrictive

DevOps & Security

Verify default umask is set to 027 or more restrictive in shell configuration files

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5.4.4 Ensure default user umask is 027 or more restrictive (Scored)

Profile Applicability

Level 1 - Server
Level 1 - Workstation

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.

Rationale

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.

Audit Procedure

Run the following commands and verify all umask lines returned are 027 or more restrictive:

grep "umask" /etc/bash.bashrc
grep "umask" /etc/profile /etc/profile.d/*.sh

Expected Result

umask 027

Remediation

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

Default Value

umask 022

References

CIS Controls: 13 - Data Protection

Profile

Level 1 - Server
Level 1 - Workstation