---
id: CVE-2026-98621
title: 'net: gue: reject invalid REMCSUM offsets'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net: gue: reject invalid REMCSUM offsets

  The REMCSUM option carries an absolute checksum start and checksum field
  offset. gue_remcsum() passes them to skb_remcsum_proc…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= fe881ef11cf0220f118816181930494d484c4883 <
    4b9bc21b2396c396d88dd909caaf73d5be6ff593
  - >-
    Linux >= fe881ef11cf0220f118816181930494d484c4883 <
    43efb1f997e976f386aa89716f55870cd2cff9ad
  - >-
    Linux >= fe881ef11cf0220f118816181930494d484c4883 <
    1eeec0c51fd5598da44080ed96bbd9880021c28b
  - >-
    Linux >= fe881ef11cf0220f118816181930494d484c4883 <
    1d664be4ca49d1696e85239236f4988dfc4653c3
  - >-
    Linux >= fe881ef11cf0220f118816181930494d484c4883 <
    97f907203321eee2cc9132d5c9eb47698fb41d35
  - >-
    Linux >= fe881ef11cf0220f118816181930494d484c4883 <
    40aeafbcbc7bc4018e8f74bbbb4d29ed8846f57f
  - >-
    Linux >= fe881ef11cf0220f118816181930494d484c4883 <
    c20f755338ca234e523dfc943719f194dfc1f903
  - >-
    Linux >= fe881ef11cf0220f118816181930494d484c4883 <
    2566866fc30965d915d0b52b5c3323b362619f0e
  - Linux 4.0
published: '2026-10-18'
updated: '2026-10-18'
sourceUpdated: '2026-10-18T15:19:41.211Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-98621'
references:
  - url: 'https://git.kernel.org/stable/c/4b9bc21b2396c396d88dd909caaf73d5be6ff593'
  - url: 'https://git.kernel.org/stable/c/43efb1f997e976f386aa89716f55870cd2cff9ad'
  - url: 'https://git.kernel.org/stable/c/1eeec0c51fd5598da44080ed96bbd9880021c28b'
  - url: 'https://git.kernel.org/stable/c/1d664be4ca49d1696e85239236f4988dfc4653c3'
  - url: 'https://git.kernel.org/stable/c/97f907203321eee2cc9132d5c9eb47698fb41d35'
  - url: 'https://git.kernel.org/stable/c/40aeafbcbc7bc4018e8f74bbbb4d29ed8846f57f'
  - url: 'https://git.kernel.org/stable/c/c20f755338ca234e523dfc943719f194dfc1f903'
  - url: 'https://git.kernel.org/stable/c/2566866fc30965d915d0b52b5c3323b362619f0e'
tags:
  - cve.org
ingestedAt: '2026-10-18T15:45:12.239Z'
---

## Overview

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

net: gue: reject invalid REMCSUM offsets

The REMCSUM option carries an absolute checksum start and checksum field
offset. gue_remcsum() passes them to skb_remcsum_process(), whose
partial path stores offset - start in the u16 skb->csum_offset variable.
If offset is less than start, this underflows.

A forwarded packet can retain CHECKSUM_PARTIAL and reach a NETIF_F_HW_CSUM
driver which trusts the metadata, leading skb_copy_and_csum_dev() to write
two bytes about 64 KiB beyond the destination buffer.

Reject reversed tuples in validate_gue_flags(), after the existing length
validation, so all GUE parsers enforce the ordering in one place.

## Affected

- `Linux >= fe881ef11cf0220f118816181930494d484c4883 < 4b9bc21b2396c396d88dd909caaf73d5be6ff593`
- `Linux >= fe881ef11cf0220f118816181930494d484c4883 < 43efb1f997e976f386aa89716f55870cd2cff9ad`
- `Linux >= fe881ef11cf0220f118816181930494d484c4883 < 1eeec0c51fd5598da44080ed96bbd9880021c28b`
- `Linux >= fe881ef11cf0220f118816181930494d484c4883 < 1d664be4ca49d1696e85239236f4988dfc4653c3`
- `Linux >= fe881ef11cf0220f118816181930494d484c4883 < 97f907203321eee2cc9132d5c9eb47698fb41d35`
- `Linux >= fe881ef11cf0220f118816181930494d484c4883 < 40aeafbcbc7bc4018e8f74bbbb4d29ed8846f57f`
- `Linux >= fe881ef11cf0220f118816181930494d484c4883 < c20f755338ca234e523dfc943719f194dfc1f903`
- `Linux >= fe881ef11cf0220f118816181930494d484c4883 < 2566866fc30965d915d0b52b5c3323b362619f0e`
- `Linux 4.0`

## Remediation

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