Disable Accepting Packets Routed Between Local Interfaces
Sets net.ipv4.conf.all.accept_local=0 so the kernel rejects inbound packets that spoof one of the host's own local source addresses.
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
When net.ipv4.conf.all.accept_local=1, the kernel accepts packets arriving on an interface whose source address is one of the host's own local addresses (including the 127.0.0.0/8 loopback block). An attacker on the wire can craft such spoofed packets to impersonate the host to itself and bypass filters that trust local source addresses. Setting it to 0 makes the kernel treat these as invalid (martian) packets and drop them, closing a local-address spoofing vector. This is rarely needed outside of specific routing setups.
What Pavois checks
Pavois reads the live kernel value via kernel_parameter('net.ipv4.conf.all.accept_local') and asserts it equals 0. The all key sets the effective default the kernel applies; reading the running value catches a drop-in that was written but never reloaded, or one overridden by a later file. A file-only scan of sysctl.d cannot prove what the kernel is actually enforcing on incoming packets.
describe kernel_parameter('net.ipv4.conf.all.accept_local') do
its('value') { should cmp 0 }
end
describe command("grep -hsE '^[[:space:]]*net.ipv4.conf.all.accept_local[[: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.ipv4.conf.all.accept_local. Expected output:
net.ipv4.conf.all.accept_local = 0
Inspect & investigate
sysctl net.ipv4.conf.all.accept_localshows the current value.cat /proc/sys/net/ipv4/conf/all/accept_localis the raw kernel value.- Packets dropped as martian are only logged if
log_martiansis enabled, see the relatedsysctl-net-ipv4-conf-all-log_martiansrule, after which dropped spoofed packets appear indmesg/journalctl -kasmartian sourceentries.
Remediation
Pavois's harden plan uses the sysctl resource to set net.ipv4.conf.all.accept_local to 0. It writes the key into a Pavois-managed drop-in and reloads it so the setting is active immediately and persistent across reboots. Apply it with pavois harden apply.
Pavois applies this with its own harden engine, the plan below, not a shell script:
| key | net.ipv4.conf.all.accept_local |
|---|---|
| resource | sysctl |
| value | 0 |
pavois harden plan localwhere the target is local, a user@host SSH alias, or a container , Docs
Impact & precautions
For a standard host this is the safe default and has no effect on normal traffic. The exception is a niche topology where you deliberately route packets between two of the host's own interfaces over the wire (some load-balancing or multi-homed router designs rely on accept_local=1). Before applying, confirm the host is not such a router; if it is, this rule will break that path and you should scope the relaxation to the specific interface rather than disabling the protection globally.
Standards mapping
| Standard | Reference | Type | Version | Confidence |
|---|---|---|---|---|
| ANSSI BP-028 | R12 | 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.