Disable Accepting ICMP Redirects for All IPv6 Interfaces
Sets net.ipv6.conf.all.accept_redirects to 0 so the host ignores ICMPv6 redirect messages on all interfaces.
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
An ICMPv6 redirect tells a host to use a different next-hop router for a destination. Because these messages are unauthenticated, an attacker on the local link can forge a redirect to insert a malicious gateway into the host's routing cache, enabling a man-in-the-middle attack or traffic blackholing. End hosts rarely need to act on redirects; ignoring them removes this avenue.
What Pavois checks
Pavois reads the effective runtime value via the kernel_parameter resource (equivalent to sysctl net.ipv6.conf.all.accept_redirects) and asserts it is 0. The live kernel value is authoritative: a value declared in /etc/sysctl.conf or /etc/sysctl.d/* may be overridden by a later drop-in or never loaded, so a file-only scanner (OVAL/oscap) can report compliant while the kernel still accepts redirects.
describe kernel_parameter('net.ipv6.conf.all.accept_redirects') do
its('value') { should cmp 0 }
end
describe command("grep -hsE '^[[:space:]]*net.ipv6.conf.all.accept_redirects[[: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.all.accept_redirects (or cat /proc/sys/net/ipv6/conf/all/accept_redirects). Expected output:
net.ipv6.conf.all.accept_redirects = 0
Inspect & investigate
No dedicated log. Check the live value with sysctl net.ipv6.conf.all.accept_redirects, audit its source with sysctl --system, and watch for redirect-driven route changes with ip -6 route show cache.
Remediation
Pavois's harden plan uses the sysctl resource to set net.ipv6.conf.all.accept_redirects to 0, persisting it in a Pavois-owned /etc/sysctl.d/ drop-in and applying it live (no reboot). Run it with pavois harden apply.
Pavois applies this with its own harden engine, the plan below, not a shell script:
| key | net.ipv6.conf.all.accept_redirects |
|---|---|
| resource | sysctl |
| value | 0 |
pavois harden plan localwhere the target is local, a user@host SSH alias, or a container , Docs
Impact & precautions
Negligible on end systems and servers: legitimate ICMPv6 redirects only optimise routing within a single subnet, and modern networks do not depend on them. After applying, the host simply keeps its configured/default route instead of adopting redirect-suggested next hops. Do not enforce on routers that intentionally process redirects. No risk of lockout.
Standards mapping
| Standard | Reference | Type | Version | Confidence |
|---|---|---|---|---|
| ANSSI BP-028 | R13 | direct | 2.0 | high |
| CIS | 3.3.5, 3.3.2.3 | direct | per OS, see the benchmark table | high |
| NIST | 3.1.20, CM-6, CM-6(a), CM-6(b), CM-7(a), CM-7(b) | supporting | 800-53 Rev 5 · 800-171 Rev 2 (pinned) | medium |
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.