Profile Applicability:
Level 1

Description:
 The /etc/shells file lists valid login shells on the system. Improper permissions on this file can allow unauthorized modification, potentially enabling users to set malicious shells.

Rationale:
 Securing permissions on /etc/shells prevents unauthorized changes that could compromise user authentication and shell access.

Impact:
 Pros:

  • Protects the integrity of allowed login shells.

  • Prevents security risks from unauthorized shell changes.

Cons:

  • Overly restrictive permissions might affect system utilities reading the file.

Default Value:
 Permissions on /etc/shells are typically set to allow read access by all users.

Pre-requisites:

  • Root or sudo privileges to audit and modify file permissions.

Remediation:

Test Plan:

Using Linux command line:

  1. Check current permissions of /etc/shells:

    ls -l /etc/shells

  2. Verify ownership is root:root and permissions are set to 644 or more restrictive.

Implementation Plan:

Using Linux command line:

  1. Set ownership to root:

    chown root:root /etc/shells

  2. Set permissions to 644:

    chmod 644 /etc/shells

  3. Verify changes:

    ls -l /etc/shells


Backout Plan:

Using Linux command line:

  1. Restore previous permissions and ownership from backup if necessary.

  2. Confirm system utilities operate correctly after changes.

References: