Cis Ubuntu2004 V300 5 2 2

Ensure sudo commands use pty (Automated)

Profile Applicability

• Level 1 - Server
• Level 1 - Workstation

Description

sudo can be configured to run only from a pseudo terminal (pseudo-pty).

Rationale

Attackers can run a malicious program using sudo which would fork a background process that remains even when the main program has finished executing.

Impact

WARNING: Editing the sudo configuration incorrectly can cause sudo to stop functioning. Always use visudo to modify sudo configuration files.

Audit Procedure

Command Line

Verify that sudo can only run other commands from a pseudo terminal. Run the following command to verify Defaults use_pty is set:

# grep -rPi -- '^\h*Defaults\h+([^#\n\r]+,\h*)?use_pty\b' /etc/sudoers*

Verify the output matches:

/etc/sudoers:Defaults use_pty

Run the follow command to to verify Defaults !use_pty is not set:

# grep -rPi -- '^\h*Defaults\h+([^#\n\r]+,\h*)?!use_pty\b' /etc/sudoers*

Nothing should be returned.

Expected Result

Defaults use_pty should be set in /etc/sudoers and !use_pty should not be found.

Remediation

Command Line

Edit the file /etc/sudoers with visudo or a file in /etc/sudoers.d/ with visudo -f <PATH TO FILE> and add the following line:

Defaults use_pty

Edit the file /etc/sudoers with visudo and any files in /etc/sudoers.d/ with visudo -f <PATH TO FILE> and remove any occurrence of !use_pty

Note:

• sudo will read each file in /etc/sudoers.d, skipping file names that end in ~ or contain a . character to avoid causing problems with package manager or editor temporary/backup files.
• Files are parsed in sorted lexical order. That is, /etc/sudoers.d/01_first will be parsed before /etc/sudoers.d/10_second.
• Be aware that because the sorting is lexical, not numeric, /etc/sudoers.d/1_whoops would be loaded after /etc/sudoers.d/10_second.
• Using a consistent number of leading zeroes in the file names can be used to avoid such problems.

References

1. SUDO(8)
2. VISUDO(8)
3. sudoers(5)
4. NIST SP 800-53 Rev. 5: AC-6

CIS Controls

v8 - 5.4 Restrict Administrator Privileges to Dedicated Administrator Accounts Restrict administrator privileges to dedicated administrator accounts on enterprise assets. Conduct general computing activities, such as internet browsing, email, and productivity suite use, from the user's primary, non-privileged account.

v7 - 4.3 Ensure the Use of Dedicated Administrative Accounts Ensure that all users with administrative account access use a dedicated or secondary account for elevated activities. This account should only be used for administrative activities and not internet browsing, email, or similar activities.

MITRE ATT&CK Mappings: T1078, T1078.003, T1548, T1548.003 | TA0001, TA0003 | M1026, M1028