cyberstrikeus 3.2.2 Ensure ICMP redirects are not accepted (Scored)
Profile Applicability
- Level 1 - Server
- Level 1 - Workstation
Description
ICMP redirect messages are packets that convey routing information and tell your host (acting as a router) to send packets via an alternate path. It is a way of allowing an outside routing device to update your system routing tables. By setting net.ipv4.conf.all.accept_redirects to 0, the system will not accept any ICMP redirect messages, and therefore, won't allow outsiders to update the system's routing tables.
Rationale
Attackers could use bogus ICMP redirect messages to maliciously alter the system routing tables and get them to send packets to incorrect networks and allow your system packets to be captured.
Audit Procedure
Run the following commands and verify output matches:
sysctl net.ipv4.conf.all.accept_redirects
# Expected: net.ipv4.conf.all.accept_redirects = 0
sysctl net.ipv4.conf.default.accept_redirects
# Expected: net.ipv4.conf.default.accept_redirects = 0
grep "net\.ipv4\.conf\.all\.accept_redirects" /etc/sysctl.conf /etc/sysctl.d/*
# Expected: net.ipv4.conf.all.accept_redirects= 0
grep "net\.ipv4\.conf\.default\.accept_redirects" /etc/sysctl.conf /etc/sysctl.d/*
# Expected: net.ipv4.conf.default.accept_redirects= 0
Expected Result
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.default.accept_redirects = 0
Remediation
Set the following parameters in /etc/sysctl.conf or a /etc/sysctl.d/* file:
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.default.accept_redirects = 0
Run the following commands to set the active kernel parameters:
sysctl -w net.ipv4.conf.all.accept_redirects=0
sysctl -w net.ipv4.conf.default.accept_redirects=0
sysctl -w net.ipv4.route.flush=1
Default Value
Not specified.
References
- CIS Controls: 3 - Secure Configurations for Hardware and Software on Mobile Devices, Laptops, Workstations, and Servers
- CIS Controls: 11 - Secure Configurations for Network Devices such as Firewalls, Routers and switches
Profile
- Level 1 - Server
- Level 1 - Workstation