CVE-2026-31665

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

netfilter: nft_ct: fix use-after-free in timeout object destroy

nft_ct_timeout_obj_destroy() frees the timeout object with kfree()

immediately after nf_ct_untimeout(), without waiting for an RCU grace

period. Concurrent packet processing on other CPUs may still hold

RCU-protected references to the timeout object obtained via

rcu_dereference() in nf_ct_timeout_data().

Add an rcu_head to struct nf_ct_timeout and use kfree_rcu() to defer

freeing until after an RCU grace period, matching the approach already

used in nfnetlink_cttimeout.c.

KASAN report:

BUG: KASAN: slab-use-after-free in nf_conntrack_tcp_packet+0x1381/0x29d0

Read of size 4 at addr ffff8881035fe19c by task exploit/80

Call Trace:

nf_conntrack_tcp_packet+0x1381/0x29d0

nf_conntrack_in+0x612/0x8b0

nf_hook_slow+0x70/0x100

__ip_local_out+0x1b2/0x210

tcp_sendmsg_locked+0x722/0x1580

__sys_sendto+0x2d8/0x320

Allocated by task 75:

nft_ct_timeout_obj_init+0xf6/0x290

nft_obj_init+0x107/0x1b0

nf_tables_newobj+0x680/0x9c0

nfnetlink_rcv_batch+0xc29/0xe00

Freed by task 26:

nft_obj_destroy+0x3f/0xa0

nf_tables_trans_destroy_work+0x51c/0x5c0

process_one_work+0x2c4/0x5a0