cis-ubuntu2004-v300-3-2-1

3.2.1 Ensure dccp kernel module is not available (Automated)

Profile

• Level 2 - Server
• Level 2 - Workstation

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 expected if the DCCP protocol is not in use.

Audit Procedure

Command Line

Verify the dccp kernel module is not available on the system or has been disabled. This can be verified by performing the following or by running the audit script included below.

Run the following script to determine if the dccp kernel module is available on the system:

#!/usr/bin/env bash

{
  l_mod_name="dccp" l_mod_type="net"
  while IFS= read -r l_mod_path; do
      if [ -d "$l_mod_path/${l_mod_name//\-/\/}" ] && [ -n "$(ls -A "$l_mod_path/${l_mod_name//\-/\/}")" ]; then
          printf '%s\n' "$l_mod_name exists in $l_mod_path"
      fi
  done < <(readlink -f /usr/lib/modules/**/kernel/$l_mod_type || readlink -f
/lib/modules/**/kernel/$l_mod_type)
}

If nothing is returned, the dccp kernel module is not available on the system and no further audit steps are required. Note: Some systems may include the dccp filesystem as part of the kernel opposed to being available as a kernel module. In this case, the above audit will not return anything. This is also considered a passing state.

If anything is returned, verify the dccp kernel module is not loaded and not loadable by performing the following:

Run the following command to verify the dccp kernel module is not loaded:

# lsmod | grep 'dccp'

Nothing should be returned.

Run the following command to verify the dccp kernel module is not loadable:

# modprobe --showconfig | grep -P -- '\b(install|blacklist)\h+dccp\b'

Verify the output includes:

blacklist dccp
 -AND-
install dccp /bin/false
 -OR-
install dccp /bin/true

Expected Result

The dccp kernel module should not be available, or if present, it should be blacklisted and set to install /bin/false or /bin/true, and not currently loaded.

Remediation

Command Line

Run the following to unload and disable the dccp kernel module. This can also be done by running the script included below.

Run the following commands to unload the dccp kernel module:

# modprobe -r dccp 2>/dev/null
# rmmod dccp 2>/dev/null

Perform the following to disable the dccp kernel module: Create a file ending in .conf with install dccp /bin/false in the /etc/modprobe.d/ directory. Example:

# printf '\n%s\n' "install dccp /bin/false" >> dccp.conf

Create a file ending in .conf with blacklist dccp in the /etc/modprobe.d/ directory. Example:

# printf '\n%s\n' "blacklist dccp" >> dccp.conf

Default Value

dccp kernel module is available but not loaded by default.

References

1. NIST SP 800-53 Rev. 5: SI-4, CM-7

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