Linux kernel: netfilter xtables NFPROTO_ARP hook validation flaw
CVE-2026-31424 Published on April 13, 2026
netfilter: x_tables: restrict xt_check_match/xt_check_target extensions for NFPROTO_ARP
In the Linux kernel, the following vulnerability has been resolved:
netfilter: x_tables: restrict xt_check_match/xt_check_target extensions for NFPROTO_ARP
Weiming Shi says:
xt_match and xt_target structs registered with NFPROTO_UNSPEC can be
loaded by any protocol family through nft_compat. When such a
match/target sets .hooks to restrict which hooks it may run on, the
bitmask uses NF_INET_* constants. This is only correct for families
whose hook layout matches NF_INET_*: IPv4, IPv6, INET, and bridge
all share the same five hooks (PRE_ROUTING ... POST_ROUTING).
ARP only has three hooks (IN=0, OUT=1, FORWARD=2) with different
semantics. Because NF_ARP_OUT == 1 == NF_INET_LOCAL_IN, the .hooks
validation silently passes for the wrong reasons, allowing matches to
run on ARP chains where the hook assumptions (e.g. state->in being
set on input hooks) do not hold. This leads to NULL pointer
dereferences; xt_devgroup is one concrete example:
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000044: 0000 [#1] SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000220-0x0000000000000227]
RIP: 0010:devgroup_mt+0xff/0x350
Call Trace:
<TASK>
nft_match_eval (net/netfilter/nft_compat.c:407)
nft_do_chain (net/netfilter/nf_tables_core.c:285)
nft_do_chain_arp (net/netfilter/nft_chain_filter.c:61)
nf_hook_slow (net/netfilter/core.c:623)
arp_xmit (net/ipv4/arp.c:666)
</TASK>
Kernel panic - not syncing: Fatal exception in interrupt
Fix it by restricting arptables to NFPROTO_ARP extensions only.
Note that arptables-legacy only supports:
- arpt_CLASSIFY
- arpt_mangle
- arpt_MARK
that provide explicit NFPROTO_ARP match/target declarations.
Products Associated with CVE-2026-31424
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Affected Versions
Linux:- Version 9291747f118d6404e509747b85ff5f6dfec368d2 and below 80e3c75f71c3ea1e62fcb032382de13e00a68f8b is affected.
- Version 9291747f118d6404e509747b85ff5f6dfec368d2 and below d9a0af9e43416aa50c0595e15fa01365a1c72c49 is affected.
- Version 9291747f118d6404e509747b85ff5f6dfec368d2 and below 1cd6313c8644bfebbd813a05da9daa21b09dd68c is affected.
- Version 9291747f118d6404e509747b85ff5f6dfec368d2 and below f00ac65c90ea475719e08d629e2e26c8b4e6999b is affected.
- Version 9291747f118d6404e509747b85ff5f6dfec368d2 and below e7e1b6bcb389c8708003d40613a59ff2496f6b1f is affected.
- Version 9291747f118d6404e509747b85ff5f6dfec368d2 and below dc3e27dd7d76e21106b8f9bbdc31f5da74a89014 is affected.
- Version 9291747f118d6404e509747b85ff5f6dfec368d2 and below 3e79374b03bf9a2f282f0eb1d0ac3776f7e0f28a is affected.
- Version 9291747f118d6404e509747b85ff5f6dfec368d2 and below 3d5d488f11776738deab9da336038add95d342d1 is affected.
- Version 2.6.39 is affected.
- Before 2.6.39 is unaffected.
- Version 5.10.253, <= 5.10.* is unaffected.
- Version 5.15.203, <= 5.15.* is unaffected.
- Version 6.1.168, <= 6.1.* is unaffected.
- Version 6.6.134, <= 6.6.* is unaffected.
- Version 6.12.81, <= 6.12.* is unaffected.
- Version 6.18.22, <= 6.18.* is unaffected.
- Version 6.19.12, <= 6.19.* is unaffected.
- Version 7.0, <= * is unaffected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.