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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.
| Product | Vendor Advisory | Solution File | Added | Published |
|---|---|---|---|---|
| Amazon_linux_2023 | — | Upgrade kernel6.18-develUpgrade kernel6.18-debuginfo-common-x86_64Upgrade perf6.18Upgrade kernel6.18-tools-develUpgrade python3-perf6.18-debuginfoUpgrade kernel6.18-tools-debuginfoUpgrade perf6.18-debuginfoUpgrade python3-perf6.18Upgrade bpftool6.18Upgrade bpftool6.18-debuginfoUpgrade kernel6.18-debuginfoUpgrade kernel6.18-headersUpgrade kernel6.18-toolsUpgrade kernel-livepatch-6.18.56-125.164Upgrade kernel6.18Upgrade kernel6.18-debuginfo-common-aarch64Upgrade microvm-kernel6.18Upgrade kernel6.18-modules-extraUpgrade kernel6.18-modules-extra-common | Oct 28, 2026 | Oct 7, 2026 |
| Debian | — | Upgrade linuxUpgrade linux-6.12 | Oct 20, 2026 | Oct 7, 2026 |
| Redhat_linux | — | No solution exists | Oct 13, 2026 | Oct 7, 2026 |
| Vmware Photon_os | — | Use 'tdnf update' to upgrade all packages to the latest version. | Oct 13, 2026 | Oct 7, 2026 |
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