---
id: CVE-2026-98955
title: 'flow_dissector: avoid u16 truncation of skb->len when computing thoff'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  flow_dissector: avoid u16 truncation of skb->len when computing thoff

  __skb_flow_dissect() computes key_control->thoff using:

    key_control->thoff = min_t(u16, nhoff,…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= d0c081b49137cd3200f2023c0875723be66e7ce5 <
    d9e08836d06c84abb18470c94b12b131eaccdc7d
  - >-
    Linux >= d0c081b49137cd3200f2023c0875723be66e7ce5 <
    50d0cd575cab763f833d6ac6eb6550b23a0b3dae
  - >-
    Linux >= d0c081b49137cd3200f2023c0875723be66e7ce5 <
    9993e6a0ac1b5b3101ffba702cacb9f42b9909d8
  - >-
    Linux >= d0c081b49137cd3200f2023c0875723be66e7ce5 <
    52efce4755a4b8b82039caa773645ffc80b25362
  - >-
    Linux >= d0c081b49137cd3200f2023c0875723be66e7ce5 <
    99bda1ecbd56905f8bd934b9cdccd3bd251192b1
  - Linux d35cd5e279881ec36ff8cd82a2d9caebc0cce3fc
  - Linux eecfa2eeefe3caef4c8d6b2284f6066c76ab26a1
  - Linux 80f327285cab6ab8e10c3ea03278add5dd99fb02
  - Linux >= 4.4.114 < 4.5
  - Linux >= 4.9.79 < 4.10
  - Linux >= 4.14.16 < 4.15
  - Linux 4.15
published: '2026-10-23'
updated: '2026-10-23'
sourceUpdated: '2026-10-23T12:19:15.287Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-98955'
references:
  - url: 'https://git.kernel.org/stable/c/d9e08836d06c84abb18470c94b12b131eaccdc7d'
  - url: 'https://git.kernel.org/stable/c/50d0cd575cab763f833d6ac6eb6550b23a0b3dae'
  - url: 'https://git.kernel.org/stable/c/9993e6a0ac1b5b3101ffba702cacb9f42b9909d8'
  - url: 'https://git.kernel.org/stable/c/52efce4755a4b8b82039caa773645ffc80b25362'
  - url: 'https://git.kernel.org/stable/c/99bda1ecbd56905f8bd934b9cdccd3bd251192b1'
tags:
  - cve.org
ingestedAt: '2026-10-23T13:24:55.557Z'
---

## Overview

In the Linux kernel, the following vulnerability has been resolved:

flow_dissector: avoid u16 truncation of skb->len when computing thoff

__skb_flow_dissect() computes key_control->thoff using:

  key_control->thoff = min_t(u16, nhoff, skb ? skb->len : hlen);

min_t(u16, ...) casts both arguments to u16 before comparing them.
Whenever skb->len (or hlen) modulo 65536 is smaller than nhoff, the
truncated length wins and thoff is set to a bogus small value, even
when the dissection succeeded. For example, an IPv4/TCP frame with
skb->len == 65540 and nhoff == 34 gets thoff == 4, so callers such as
skb_probe_transport_header() point the transport header inside the
Ethernet header.

Such skbs are not exotic:
- At the time of commit d0c081b49137 ("flow_dissector: properly cap
  thoff field"), AF_PACKET with PACKET_VNET_HDR could already build GSO
  skbs larger than 64KB (MTU checks are skipped for GSO, and
  alloc_skb_with_frags() accepted up to MAX_SKB_FRAGS (17) order-0
  pages on top of the linear part).
- BIG TCP now makes skbs larger than 64KB common.
- The following patch makes tun_get_user() dissect IFF_TAP frames
  before eth_type_trans() pulls the Ethernet header, so a GSO frame
  carrying a 65522..65535 byte L3 packet will be dissected with
  skb->len in [65536, 65549].

Compare as u32 instead. If the resulting offset cannot be represented
in the u16 key_control->thoff, cap it to U16_MAX and report the
dissection as failed rather than silently returning a wrong transport
offset. thoff is still set on failure, as some callers (such as
eth_get_headlen()) use it regardless of the return value.

## Affected

- `Linux >= d0c081b49137cd3200f2023c0875723be66e7ce5 < d9e08836d06c84abb18470c94b12b131eaccdc7d`
- `Linux >= d0c081b49137cd3200f2023c0875723be66e7ce5 < 50d0cd575cab763f833d6ac6eb6550b23a0b3dae`
- `Linux >= d0c081b49137cd3200f2023c0875723be66e7ce5 < 9993e6a0ac1b5b3101ffba702cacb9f42b9909d8`
- `Linux >= d0c081b49137cd3200f2023c0875723be66e7ce5 < 52efce4755a4b8b82039caa773645ffc80b25362`
- `Linux >= d0c081b49137cd3200f2023c0875723be66e7ce5 < 99bda1ecbd56905f8bd934b9cdccd3bd251192b1`
- `Linux d35cd5e279881ec36ff8cd82a2d9caebc0cce3fc`
- `Linux eecfa2eeefe3caef4c8d6b2284f6066c76ab26a1`
- `Linux 80f327285cab6ab8e10c3ea03278add5dd99fb02`
- `Linux >= 4.4.114 < 4.5`
- `Linux >= 4.9.79 < 4.10`
- `Linux >= 4.14.16 < 4.15`
- `Linux 4.15`

## Remediation

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