CVE-2026-31424

Summary

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.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/80e3c75f71c3ea1e62fcb032382de13e00a68f8b
• https://git.kernel.org/stable/c/d9a0af9e43416aa50c0595e15fa01365a1c72c49
• https://git.kernel.org/stable/c/1cd6313c8644bfebbd813a05da9daa21b09dd68c
• https://git.kernel.org/stable/c/f00ac65c90ea475719e08d629e2e26c8b4e6999b
• https://git.kernel.org/stable/c/e7e1b6bcb389c8708003d40613a59ff2496f6b1f
• https://git.kernel.org/stable/c/dc3e27dd7d76e21106b8f9bbdc31f5da74a89014
• https://git.kernel.org/stable/c/3e79374b03bf9a2f282f0eb1d0ac3776f7e0f28a
• https://git.kernel.org/stable/c/3d5d488f11776738deab9da336038add95d342d1

• ←Previous
• Next→