CVE-2026-98374tcp: fix use-after-free of retransmit_skb_hint in tcp_send_synack()

Official description

In the Linux kernel, the following vulnerability has been resolved: tcp: fix use-after-free of retransmit_skb_hint in tcp_send_synack() When tcp_send_synack() replaces the cloned SYN skb at the head of the retransmit queue with a copy, it frees the original with tcp_rtx_queue_unlink_and_free() and only repairs tp->highest_sack. tp->retransmit_skb_hint keeps pointing at the freed skbuff_fclone_cache object. The dangling hint is read in tcp_verify_retransmit_hint() and used as the root of the rbtree walk in tcp_xmit_retransmit_queue(). An unprivileged TFO client (sendmsg(MSG_FASTOPEN)) can arm the hint with an attacker-supplied ICMP fragmentation-needed message, after which a simultaneous open frees the armed SYN skb: BUG: KASAN: slab-use-after-free in tcp_mark_skb_lost (net/ipv4/tcp_input.c:1316) Read of size 4 at addr ffff88800604d928 by task swapper/1/0 Call Trace: tcp_mark_skb_lost (net/ipv4/tcp_input.c:1316) tcp_simple_retransmit (net/ipv4/tcp_input.c:3158) tcp_v4_err (net/ipv4/tcp_ipv4.c:587) Sync the hint to the copy.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/fad6d429651e748365e93ca54645accc212f0018
• https://git.kernel.org/stable/c/c5b4da1f403a658c1c19766be2b426003ada419f
• https://git.kernel.org/stable/c/71d45049b0d631dfdbf3c65305f7fca676de023b
• https://git.kernel.org/stable/c/e3ea71cb1408a013ed4e8a757b815f1a919324bd
• https://git.kernel.org/stable/c/631aa4cb45099f09e9385dd786bd291c6270bfc4
• https://git.kernel.org/stable/c/0f87720c7e4bcab07c24888b3cf12bfe857bb90e
• https://git.kernel.org/stable/c/fe99bbeee5c5dbd3abc30721a8079ced59649d97