---
id: CVE-2026-31617
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  usb: gadget: f_ncm: validate minimum block_len in ncm_unwrap_ntb()

  The block_len read from the host-supplied NTB header is checked against
  ntb_max but has no lower bou…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  usb: gadget: f_ncm: validate minimum block_len in ncm_unwrap_ntb()

  The block_len read from the host-supplied NTB header is checked against
  ntb_max but has no lower bou…
severity: medium
cvss: 5.5
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-191
vendor: linux
product: linux_kernel
affected:
  - 'linux_kernel >= 5.9, < 6.6.136'
  - 'linux_kernel >= 6.12, < 6.12.83'
  - 'linux_kernel >= 6.13, < 6.18.24'
  - 'linux_kernel >= 6.19, < 6.19.14'
  - 'linux_kernel >= 7.0, < 7.0.1'
patched:
  - linux_kernel 7.0.1
published: '2026-04-24'
updated: '2026-08-06'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-31617'
references:
  - url: 'https://git.kernel.org/stable/c/068a7f2749fff6462a0a908ec415b885fe430f50'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/0f156bb5334e588034ca68ac2ee92b23f66e56e7'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/1425655c2870054c3ab4712e2b6dbdd331597ada'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/6762f8a95772265dd0c2ffe7f400493f3115b135'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/74908b0318d1df1188457040b8714ff4d4b68126'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/8757a2593631443648218244b9788e193ae0fdc1'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/8b3b7bd3c02f98634baaf36c7fc7ac915f6517ca'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/8f993d30b95dc9557a8a96ceca11abed674c8acb'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/d58ba8f6546232f8414f396c189297dbee03f1a7'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://access.redhat.com/security/cve/CVE-2026-31617'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2461448'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-31617.json
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
tags:
  - nvd
epss: 0.00171
epssPercentile: 0.05674
ingestedAt: '2026-08-06T13:59:36.973Z'
---

## Overview

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

usb: gadget: f_ncm: validate minimum block_len in ncm_unwrap_ntb()

The block_len read from the host-supplied NTB header is checked against
ntb_max but has no lower bound. When block_len is smaller than
opts->ndp_size, the bounds check of:
	ndp_index > (block_len - opts->ndp_size)
will underflow producing a huge unsigned value that ndp_index can never
exceed, defeating the check entirely.

The same underflow occurs in the datagram index checks against block_len
- opts->dpe_size.  With those checks neutered, a malicious USB host can
choose ndp_index and datagram offsets that point past the actual
transfer, and the skb_put_data() copies adjacent kernel memory into the
network skb.

Fix this by rejecting block lengths that cannot hold at least the NTB
header plus one NDP.  This will make block_len - opts->ndp_size and
block_len - opts->dpe_size both well-defined.

Commit 8d2b1a1ec9f5 ("CDC-NCM: avoid overflow in sanity checking") fixed
a related class of issues on the host side of NCM.

## Affected

- `linux_kernel >= 5.9, < 6.6.136`
- `linux_kernel >= 6.12, < 6.12.83`
- `linux_kernel >= 6.13, < 6.18.24`
- `linux_kernel >= 6.19, < 6.19.14`
- `linux_kernel >= 7.0, < 7.0.1`

## Remediation

Upgrade past the affected range:

- `linux_kernel 7.0.1`