linux-formula/metadata/service/system/cis/cis-3-2-1.yml

# 3.2.1 Ensure source routed packets are not accepted
#
# Description
# ===========
# In networking, source routing allows a sender to partially or fully specify
# the route packets take through a network. In contrast, non-source routed
# packets travel a path determined by routers in the network. In some cases,
# systems may not be routable or reachable from some locations (e.g. private
# addresses vs. Internet routable), and so source routed packets would need
# to be used.
#
# Rationale
# =========
# Setting `net.ipv4.conf.all.accept_source_route` and
# `net.ipv4.conf.default.accept_source_route` to 0 disables the system from
# accepting source routed packets. Assume this system was capable of routing
# packets to Internet routable addresses on one interface and private addresses
# on another interface. Assume that the private addresses were not routable to
# the Internet routable addresses and vice versa. Under normal routing
# circumstances, an attacker from the Internet routable addresses could not use
# the system as a way to reach the private address systems. If, however, source
# routed packets were allowed, they could be used to gain access to the private
# address systems as the route could be specified, rather than rely on routing
# protocols that did not allow this routing.
#
# Audit
# =====
#
# Run the following commands and verify output matches:
#
#   # sysctl net.ipv4.conf.all.accept_source_route
#   net.ipv4.conf.all.accept_source_route = 0
#   # sysctl net.ipv4.conf.default.accept_source_route
#   net.ipv4.conf.default.accept_source_route = 0
#
# Remediation
# ===========
#
# Set the following parameters in the /etc/sysctl.conf file:
#
#   net.ipv4.conf.all.accept_source_route = 0
#   net.ipv4.conf.default.accept_source_route = 0
#
# Run the following commands to set the active kernel parameters:
#
#   # sysctl -w net.ipv4.conf.all.accept_source_route=0
#   # sysctl -w net.ipv4.conf.default.accept_source_route=0
#   # sysctl -w net.ipv4.route.flush=1

parameters:
  linux:
    system:
      kernel:
        sysctl:
          net.ipv4.conf.all.accept_source_route: 0
          net.ipv4.conf.default.accept_source_route: 0