Linux Kernel: TCP Use-After-Free of retransmit_skb_hint
CVE-2026-98374 Published on October 7, 2026
tcp: fix use-after-free of retransmit_skb_hint in tcp_send_synack()
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.
Products Associated with CVE-2026-98374
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Affected Versions
Linux:- Version c31b70c9968fe9c4194d1b5d06d07596a3b680de and below fad6d429651e748365e93ca54645accc212f0018 is affected.
- Version c31b70c9968fe9c4194d1b5d06d07596a3b680de and below c5b4da1f403a658c1c19766be2b426003ada419f is affected.
- Version c31b70c9968fe9c4194d1b5d06d07596a3b680de and below 71d45049b0d631dfdbf3c65305f7fca676de023b is affected.
- Version c31b70c9968fe9c4194d1b5d06d07596a3b680de and below e3ea71cb1408a013ed4e8a757b815f1a919324bd is affected.
- Version c31b70c9968fe9c4194d1b5d06d07596a3b680de and below 631aa4cb45099f09e9385dd786bd291c6270bfc4 is affected.
- Version c31b70c9968fe9c4194d1b5d06d07596a3b680de and below 0f87720c7e4bcab07c24888b3cf12bfe857bb90e is affected.
- Version c31b70c9968fe9c4194d1b5d06d07596a3b680de and below fe99bbeee5c5dbd3abc30721a8079ced59649d97 is affected.
- Version 5.11 is affected.
- Before 5.11 is unaffected.
- Version 5.15.222, <= 5.15.* is unaffected.
- Version 6.1.189, <= 6.1.* is unaffected.
- Version 6.6.158, <= 6.6.* is unaffected.
- Version 6.12.112, <= 6.12.* is unaffected.
- Version 6.18.55, <= 6.18.* is unaffected.
- Version 7.2.9, <= 7.2.* is unaffected.
- Version 7.3-rc5, <= * is unaffected.