---
id: CVE-2026-98374
title: |-
  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,…
summary: |-
  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,…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= c31b70c9968fe9c4194d1b5d06d07596a3b680de <
    fad6d429651e748365e93ca54645accc212f0018
  - >-
    Linux >= c31b70c9968fe9c4194d1b5d06d07596a3b680de <
    c5b4da1f403a658c1c19766be2b426003ada419f
  - >-
    Linux >= c31b70c9968fe9c4194d1b5d06d07596a3b680de <
    71d45049b0d631dfdbf3c65305f7fca676de023b
  - >-
    Linux >= c31b70c9968fe9c4194d1b5d06d07596a3b680de <
    e3ea71cb1408a013ed4e8a757b815f1a919324bd
  - >-
    Linux >= c31b70c9968fe9c4194d1b5d06d07596a3b680de <
    631aa4cb45099f09e9385dd786bd291c6270bfc4
  - >-
    Linux >= c31b70c9968fe9c4194d1b5d06d07596a3b680de <
    0f87720c7e4bcab07c24888b3cf12bfe857bb90e
  - >-
    Linux >= c31b70c9968fe9c4194d1b5d06d07596a3b680de <
    fe99bbeee5c5dbd3abc30721a8079ced59649d97
  - Linux 5.11
published: '2026-10-07'
updated: '2026-10-07'
sourceUpdated: '2026-10-07T13:17:23.023'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-98374'
references:
  - url: 'https://git.kernel.org/stable/c/0f87720c7e4bcab07c24888b3cf12bfe857bb90e'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/631aa4cb45099f09e9385dd786bd291c6270bfc4'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/71d45049b0d631dfdbf3c65305f7fca676de023b'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/c5b4da1f403a658c1c19766be2b426003ada419f'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/e3ea71cb1408a013ed4e8a757b815f1a919324bd'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/fad6d429651e748365e93ca54645accc212f0018'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/fe99bbeee5c5dbd3abc30721a8079ced59649d97'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
  - cve.org
ingestedAt: '2026-10-07T13:31:04.600Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.