CVE-2026-31665

Summary

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

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/c458fc1c278a65ad5381083121d39a479973ebed
• https://git.kernel.org/stable/c/c581e5c8f2b59158f62efe61c1a3dc36189081ff
• https://git.kernel.org/stable/c/f16fe84879a5280f05ebbcea593a189ba0f3e79a
• https://git.kernel.org/stable/c/070abdf1b04325b21a20a2a0c39a2208af107275
• https://git.kernel.org/stable/c/aa7cfa16f98f8ec3e6d47c34e1a8c1ae4b9b8b77
• https://git.kernel.org/stable/c/b42aca3660dc2627a29a38131597ca610dc451f9
• https://git.kernel.org/stable/c/d0983b48c10d1509fd795c155f8b1e832e1369ff
• https://git.kernel.org/stable/c/f8dca15a1b190787bbd03285304b569631160eda

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