Cis Ubuntu2004 V300 7 1 13

7.1.13 Ensure SUID and SGID files are reviewed (Manual)

Profile

• Level 1 - Server
• Level 1 - Workstation

Description

The owner of a file can set the file's permissions to run with the owner's or group's permissions, even if the user running the program is not the owner or a member of the group. The most common reason for a SUID or SGID program is to enable users to perform functions (such as changing their password) that require root privileges.

Rationale

There are valid reasons for SUID and SGID programs, but it is important to identify and review such programs to ensure they are legitimate. Review the files returned by the action in the audit section and check to see if system binaries have a different checksum than what from the package. This is an indication that the binary may have been replaced.

Impact

None

Audit Procedure

Command Line

Run the following script to generate a list of SUID and SGID files:

#!/usr/bin/env bash

{
    l_output="" l_output2=""
    a_suid=(); a_sgid=() # initialize arrays
    while IFS= read -r l_mount; do
        while IFS= read -r -d $'\0' l_file; do
            if [ -e "$l_file" ]; then
                l_mode="$(stat -Lc '%#a' "$l_file")"
                [ $(( $l_mode & 04000 )) -gt 0 ] && a_suid+=("$l_file")
                [ $(( $l_mode & 02000 )) -gt 0 ] && a_sgid+=("$l_file")
            fi
        done < <(find "$l_mount" -xdev -type f \( -perm -2000 -o -perm -4000 \) -print0 2>/dev/null)
    done < <(findmnt -Dkerno fstype,target,options | awk '{$1 !~ /^\s*(nfs|proc|smb|vfat|iso9660|efivarfs|selinuxfs)/ && $2 !~ /^\/run\/user\// && $3 !~/noexec/ && $3 !~/nosuid/) {print $2}')
    if ! (( ${#a_suid[@]} > 0 )); then
        l_output="$l_output\n - No executable SUID files exist on the system"
    else
        l_output2="$l_output2\n - List of \"$(printf '%s' "${#a_suid[@]}")\" SUID executable files:\n$(printf '%s\n' "${a_suid[@]}")\n   - end of list -\n"
    fi
    if ! (( ${#a_sgid[@]} > 0 )); then
        l_output="$l_output\n - No SGID files exist on the system"
    else
        l_output2="$l_output2\n - List of \"$(printf '%s' "${#a_sgid[@]}")\" SGID executable files:\n$(printf '%s\n' "${a_sgid[@]}")\n   - end of list -\n"
    fi
    [ -n "$l_output2" ] && l_output2="$l_output2\n- Review the preceding list(s) of SUID and/or SGID files to\nensure that no rogue programs have been introduced onto the system.\n"
    unset a_arr; unset a_suid; unset a_sgid # Remove arrays
    if [ -z "$l_output2" ]; then
        echo -e "\n- Audit Result:\n$l_output\n"
    else
        echo -e "\n- Audit Result:\n$l_output2\n"
        [ -n "$l_output" ] && echo -e "$l_output\n"
    fi
}

Note: on systems with a large number of files, this may be a long running process.

Expected Result

Review the list of SUID and SGID files to ensure no rogue programs have been introduced onto the system.

Remediation

Command Line

Ensure that no rogue SUID or SGID programs have been introduced into the system. Review the files returned by the action in the Audit section and confirm the integrity of these binaries.

Default Value

N/A

References

1. NIST SP 800-53 Rev. 5: CM-1, CM-2, CM-6, CM-7, IA-5, AC-3, MP-2

CIS Controls

MITRE ATT&CK Mappings: