Configure Accepting Router Preference in Router Advertisements on All IPv6 Interfaces By Default
Sets the default for new IPv6 interfaces to ignore the router-preference field of Router Advertisements via net.ipv6.conf.default.accept_ra_rtr_pref = 0.
Checked against the resolved running state (e.g. sshd -T, sysctl, systemctl show), catches drop-ins and Includes a file read would miss. Caveat: runtime ≠ persistence; a value correct now may not survive a reboot.
Pavois asserts the effective configuration, the live, resolved state, not a file. File-based scanners (OVAL/SCAP, Lynis) miss Includes, drop-ins and runtime defaults; this check sees what is actually applied.
A mapping is a cross-reference to where each standard places this requirement, anchored and cross-validated, not a claim of equivalence. A passing check is evidence toward these references, how to read it.
Why this rule matters
net.ipv6.conf.default.accept_ra_rtr_pref controls whether the host honours the Router Preference field of Router Advertisements to pick its default router. If enabled, a malicious host can advertise itself with a high preference and make the system prefer an attacker-controlled gateway, enabling a man-in-the-middle position over IPv6 traffic. Disabling it by default removes the attacker's ability to influence default-router selection through forged RAs.
What Pavois checks
Pavois reads the effective kernel value of net.ipv6.conf.default.accept_ra_rtr_pref, not a config file. The live value merges /etc/sysctl.conf, drop-ins in /etc/sysctl.d/ and /run/sysctl.d/, kernel boot parameters and runtime sysctl -w. A clean file does not guarantee a clean running kernel, Pavois reports the actual enforced value.
describe kernel_parameter('net.ipv6.conf.default.accept_ra_rtr_pref') do
its('value') { should cmp 0 }
end
describe command("grep -hsE '^[[:space:]]*net.ipv6.conf.default.accept_ra_rtr_pref[[:space:]]*=[[:space:]]*0([[:space:]]|$)' /etc/sysctl.conf /etc/sysctl.d/*.conf /run/sysctl.d/*.conf /usr/lib/sysctl.d/*.conf /lib/sysctl.d/*.conf 2>/dev/null") do
its('stdout') { should match(/\S/) }
endHow to verify it is applied
Run sysctl net.ipv6.conf.default.accept_ra_rtr_pref and confirm the output is net.ipv6.conf.default.accept_ra_rtr_pref = 0.
Inspect & investigate
No dedicated log. Inspect runtime state with sysctl net.ipv6.conf.default.accept_ra_rtr_pref and sysctl -a | grep accept_ra_rtr_pref. To find which file set it, run sysctl --system 2>&1 | grep accept_ra_rtr_pref. The currently selected default router is visible via ip -6 route show default.
Remediation
Pavois's harden plan uses the sysctl resource to set net.ipv6.conf.default.accept_ra_rtr_pref = 0, persisting it in a managed drop-in and applying it live. Run pavois harden apply to enforce it; it is re-applied at boot via the persisted entry.
Pavois applies this with its own harden engine, the plan below, not a shell script:
| key | net.ipv6.conf.default.accept_ra_rtr_pref |
|---|---|
| resource | sysctl |
| value | 0 |
pavois harden plan localwhere the target is local, a user@host SSH alias, or a container , Docs
Impact & precautions
Low operational impact: this only stops the host from ranking routers by their advertised preference. On a SLAAC client that legitimately accepts RAs, default-router selection falls back to other criteria, which is acceptable. The change is safe on routers and statically-addressed servers. If the host depends on RA-based addressing, apply it together with the other accept_ra* rules for a coherent IPv6 posture.
Standards mapping
| Standard | Reference | Type | Version | Confidence |
|---|---|---|---|---|
| ANSSI BP-028 | R13 | direct | 2.0 | high |
Each reference is a cross-reference anchored in the upstream benchmark and cross-validated against the SCAP Security Guide and ansible-lockdown, not a claim of equivalence. Direct = a prescriptive, line-level requirement; supporting = an abstract control family (NIST) the check provides evidence toward. How to read a mapping.