CVE-2026-23231

In the Linux kernel, the following vulnerability has been resolved:

netfilter: nf_tables: fix use-after-free in nf_tables_addchain()

nf_tables_addchain() publishes the chain to table->chains via list_add_tail_rcu() (in nft_chain_add()) before registering hooks. If nf_tables_register_hook() then fails, the error path calls nft_chain_del() (list_del_rcu()) followed by nf_tables_chain_destroy() with no RCU grace period in between.

This creates two use-after-free conditions:

1. Control-plane: nf_tables_dump_chains() traverses table->chains under rcu_read_lock(). A concurrent dump can still be walking the chain when the error path frees it.

2. Packet path: for NFPROTO_INET, nf_register_net_hook() briefly installs the IPv4 hook before IPv6 registration fails. Packets entering nft_do_chain() via the transient IPv4 hook can still be dereferencing chain->blob_gen_X when the error path frees the chain.

Add synchronize_rcu() between nft_chain_del() and the chain destroy so that all RCU readers – both dump threads and in-flight packet evaluation – have finished before the chain is freed.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/2a6586ecfa4ce1413daaafee250d2590e05f1a33
• https://git.kernel.org/stable/c/2f9a4ffeb763aec822f8ff3d1e82202d27d46d4b
• https://git.kernel.org/stable/c/7017745068a9068904e1e7a1b170a5785647cc81
• https://git.kernel.org/stable/c/71e99ee20fc3f662555118cf1159443250647533
• https://git.kernel.org/stable/c/dbd0af8083dd201f07c49110b2ee93710abdff28
• https://git.kernel.org/stable/c/f3fe58ce37926a10115ede527d59b91bcc05400a
• https://cert-portal.siemens.com/productcert/html/ssa-253495.html