---
id: CVE-2023-53667
title: 'net: cdc_ncm: Deal with too low values of dwNtbOutMaxSize'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net: cdc_ncm: Deal with too low values of dwNtbOutMaxSize

  Currently in cdc_ncm_check_tx_max(), if dwNtbOutMaxSize is lower than
  the calculated "min" value, but greater…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 289507d3364f96f4b8814726917d572f71350d87 <
    2334ff0b343ba6ba7a6c0586fcc83992bbbc1776
  - >-
    Linux >= 289507d3364f96f4b8814726917d572f71350d87 <
    bf415bfe7573596ac213b4fd1da9e62cfc9a9413
  - >-
    Linux >= 289507d3364f96f4b8814726917d572f71350d87 <
    ff484163dfb61b58f23e4dbd007de1094427669c
  - >-
    Linux >= 289507d3364f96f4b8814726917d572f71350d87 <
    42b78c8cc774b47023d6d16d96d54cc7015e4a07
  - >-
    Linux >= 289507d3364f96f4b8814726917d572f71350d87 <
    9be921854e983a81a0aeeae5febcd87093086e46
  - >-
    Linux >= 289507d3364f96f4b8814726917d572f71350d87 <
    6147745d43ff4e0d2c542e5b93e398ef0ee4db00
  - >-
    Linux >= 289507d3364f96f4b8814726917d572f71350d87 <
    72d0240b0ee4794efc683975c213e4b384fea733
  - >-
    Linux >= 289507d3364f96f4b8814726917d572f71350d87 <
    7e01c7f7046efc2c7c192c3619db43292b98e997
  - Linux 3.16
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-11-05T20:26:42.958525Z'
published: '2025-10-07'
updated: '2026-11-05'
sourceUpdated: '2026-11-05T20:31:19.935Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2023-53667'
references:
  - url: 'https://git.kernel.org/stable/c/2334ff0b343ba6ba7a6c0586fcc83992bbbc1776'
  - url: 'https://git.kernel.org/stable/c/bf415bfe7573596ac213b4fd1da9e62cfc9a9413'
  - url: 'https://git.kernel.org/stable/c/ff484163dfb61b58f23e4dbd007de1094427669c'
  - url: 'https://git.kernel.org/stable/c/42b78c8cc774b47023d6d16d96d54cc7015e4a07'
  - url: 'https://git.kernel.org/stable/c/9be921854e983a81a0aeeae5febcd87093086e46'
  - url: 'https://git.kernel.org/stable/c/6147745d43ff4e0d2c542e5b93e398ef0ee4db00'
  - url: 'https://git.kernel.org/stable/c/72d0240b0ee4794efc683975c213e4b384fea733'
  - url: 'https://git.kernel.org/stable/c/7e01c7f7046efc2c7c192c3619db43292b98e997'
tags:
  - cve.org
epss: 0.00149
epssPercentile: 0.04084
ingestedAt: '2026-11-05T22:38:31.824Z'
---

## Overview

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

net: cdc_ncm: Deal with too low values of dwNtbOutMaxSize

Currently in cdc_ncm_check_tx_max(), if dwNtbOutMaxSize is lower than
the calculated "min" value, but greater than zero, the logic sets
tx_max to dwNtbOutMaxSize. This is then used to allocate a new SKB in
cdc_ncm_fill_tx_frame() where all the data is handled.

For small values of dwNtbOutMaxSize the memory allocated during
alloc_skb(dwNtbOutMaxSize, GFP_ATOMIC) will have the same size, due to
how size is aligned at alloc time:
	size = SKB_DATA_ALIGN(size);
        size += SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
Thus we hit the same bug that we tried to squash with
commit 2be6d4d16a084 ("net: cdc_ncm: Allow for dwNtbOutMaxSize to be unset or zero")

Low values of dwNtbOutMaxSize do not cause an issue presently because at
alloc_skb() time more memory (512b) is allocated than required for the
SKB headers alone (320b), leaving some space (512b - 320b = 192b)
for CDC data (172b).

However, if more elements (for example 3 x u64 = [24b]) were added to
one of the SKB header structs, say 'struct skb_shared_info',
increasing its original size (320b [320b aligned]) to something larger
(344b [384b aligned]), then suddenly the CDC data (172b) no longer
fits in the spare SKB data area (512b - 384b = 128b).

Consequently the SKB bounds checking semantics fails and panics:

skbuff: skb_over_panic: text:ffffffff831f755b len:184 put:172 head:ffff88811f1c6c00 data:ffff88811f1c6c00 tail:0xb8 end:0x80 dev:<NULL>
------------[ cut here ]------------
kernel BUG at net/core/skbuff.c:113!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 57 Comm: kworker/0:2 Not tainted 5.15.106-syzkaller-00249-g19c0ed55a470 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/14/2023
Workqueue: mld mld_ifc_work
RIP: 0010:skb_panic net/core/skbuff.c:113 [inline]
RIP: 0010:skb_over_panic+0x14c/0x150 net/core/skbuff.c:118
[snip]
Call Trace:
 <TASK>
 skb_put+0x151/0x210 net/core/skbuff.c:2047
 skb_put_zero include/linux/skbuff.h:2422 [inline]
 cdc_ncm_ndp16 drivers/net/usb/cdc_ncm.c:1131 [inline]
 cdc_ncm_fill_tx_frame+0x11ab/0x3da0 drivers/net/usb/cdc_ncm.c:1308
 cdc_ncm_tx_fixup+0xa3/0x100

Deal with too low values of dwNtbOutMaxSize, clamp it in the range
[USB_CDC_NCM_NTB_MIN_OUT_SIZE, CDC_NCM_NTB_MAX_SIZE_TX]. We ensure
enough data space is allocated to handle CDC data by making sure
dwNtbOutMaxSize is not smaller than USB_CDC_NCM_NTB_MIN_OUT_SIZE.

## Affected

- `Linux >= 289507d3364f96f4b8814726917d572f71350d87 < 2334ff0b343ba6ba7a6c0586fcc83992bbbc1776`
- `Linux >= 289507d3364f96f4b8814726917d572f71350d87 < bf415bfe7573596ac213b4fd1da9e62cfc9a9413`
- `Linux >= 289507d3364f96f4b8814726917d572f71350d87 < ff484163dfb61b58f23e4dbd007de1094427669c`
- `Linux >= 289507d3364f96f4b8814726917d572f71350d87 < 42b78c8cc774b47023d6d16d96d54cc7015e4a07`
- `Linux >= 289507d3364f96f4b8814726917d572f71350d87 < 9be921854e983a81a0aeeae5febcd87093086e46`
- `Linux >= 289507d3364f96f4b8814726917d572f71350d87 < 6147745d43ff4e0d2c542e5b93e398ef0ee4db00`
- `Linux >= 289507d3364f96f4b8814726917d572f71350d87 < 72d0240b0ee4794efc683975c213e4b384fea733`
- `Linux >= 289507d3364f96f4b8814726917d572f71350d87 < 7e01c7f7046efc2c7c192c3619db43292b98e997`
- `Linux 3.16`

## Remediation

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