cis-ubuntu1804-v220-3-2-1

DevOps & Security

Ensure dccp kernel module is not available

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Source SKILL.md: https://github.com/CyberStrikeus/CyberStrike/blob/HEAD/.cyberstrike/skill/CIS_benchmarks/Operating_Systems/Ubuntu/CIS_Ubuntu_Linux_18.04_LTS_Benchmark_v2.2.0/cis-ubuntu1804-v220-3-2-1/SKILL.md

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CIS Ubuntu Linux 18.04 LTS Benchmark v2.2.0 - Control 3.2.1

Description

The Datagram Congestion Control Protocol (DCCP) is a transport layer protocol that supports streaming media and telephony. DCCP provides a way to gain access to congestion control, without having to do it at the application layer, but does not provide in-sequence delivery.

Rationale

If the protocol is not required, it is recommended that the drivers not be installed to reduce the potential attack surface.

Impact

None.

Audit Procedure

Command Line

Run the following script to verify the dccp module is not available:

#!/usr/bin/bash
{
  l_mname="dccp"
  l_mtype="net"
  l_output="" l_output2="" l_output3=""
  l_dl=""

  # Check if module is currently loadable
  l_loadable="$(modprobe -n -v "$l_mname")"
  [ "$(wc -l <<< "$l_loadable")" -gt "1" ] && l_loadable="$(grep -P -- "(^\h*install|\b$l_mname)\b" <<< "$l_loadable")"
  if grep -Pq -- '^\h*install \/bin\/(true|false)' <<< "$l_loadable"; then
    l_output="$l_output\n - module: \"$l_mname\" is not loadable: \"$l_loadable\""
  else
    l_output2="$l_output2\n - module: \"$l_mname\" is loadable: \"$l_loadable\""
  fi

  # Check if the module is currently loaded
  if ! lsmod | grep "$l_mname" > /dev/null 2>&1; then
    l_output="$l_output\n - module: \"$l_mname\" is not loaded"
  else
    l_output2="$l_output2\n - module: \"$l_mname\" is loaded"
  fi

  # Check if the module is deny listed
  if modprobe --showconfig | grep -Pq -- "^\h*blacklist\h+$l_mname\b"; then
    l_output="$l_output\n - module: \"$l_mname\" is deny listed in: \"$(grep -Pl -- "^\h*blacklist\h+$l_mname\b" /etc/modprobe.d/*)\""
  else
    l_output2="$l_output2\n - module: \"$l_mname\" is not deny listed"
  fi

  # Report results
  if [ -z "$l_output2" ]; then
    echo -e "\n- Audit Result:\n ** PASS **\n$l_output\n"
  else
    echo -e "\n- Audit Result:\n ** FAIL **\n - Reason(s) for audit failure:\n$l_output2\n"
    [ -n "$l_output" ] && echo -e "\n- Correctly set:\n$l_output\n"
  fi
}

Expected Result

- Audit Result:
 ** PASS **
 - module: "dccp" is not loadable: "install /bin/true"
 - module: "dccp" is not loaded
 - module: "dccp" is deny listed in: "/etc/modprobe.d/<filename>.conf"

Remediation

Command Line

Run the following script to disable the dccp module:

#!/usr/bin/bash
{
  l_mname="dccp"
  l_mtype="net"

  if ! modprobe -n -v "$l_mname" | grep -P -- '^\h*install \/bin\/(true|false)'; then
    echo -e " - setting module: \"$l_mname\" to be not loadable"
    echo -e "install $l_mname /bin/false" >> /etc/modprobe.d/"$l_mname".conf
  fi

  if lsmod | grep "$l_mname" > /dev/null 2>&1; then
    echo -e " - unloading module \"$l_mname\""
    modprobe -r "$l_mname"
  fi

  if ! modprobe --showconfig | grep -Pq -- "^\h*blacklist\h+$l_mname\b"; then
    echo -e " - deny listing \"$l_mname\""
    echo -e "blacklist $l_mname" >> /etc/modprobe.d/"$l_mname".conf
  fi
}

Default Value

dccp module is available by default.

References

NIST SP 800-53 Rev. 5: CM-7
CIS Ubuntu Linux 18.04 LTS Benchmark v2.2.0

CIS Controls

Version 8

4.8 Uninstall or Disable Unnecessary Services on Enterprise Assets and Software - Uninstall or disable unnecessary services on enterprise assets and software.

Version 7

9.2 Ensure Only Approved Ports, Protocols and Services Are Running - Ensure that only network ports, protocols, and services listening on a system with validated business needs, are running on each system.

Profile Applicability

Level 2 - Server
Level 2 - Workstation

Assessment Status

Automated