---
id: CVE-2026-31649
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net: stmmac: fix integer underflow in chain mode

  The jumbo_frm() chain-mode implementation unconditionally computes

      len = nopaged_len - bmax;

  where nopaged_len =…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net: stmmac: fix integer underflow in chain mode

  The jumbo_frm() chain-mode implementation unconditionally computes

      len = nopaged_len - bmax;

  where nopaged_len =…
severity: critical
cvss: 9.8
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'
cwe:
  - CWE-190
  - CWE-191
vendor: linux
product: linux_kernel
affected:
  - 'linux_kernel >= 3.2.1, < 5.10.253'
  - 'linux_kernel >= 5.11, < 5.15.203'
  - 'linux_kernel >= 5.16, < 6.1.169'
  - 'linux_kernel >= 6.2, < 6.6.135'
  - 'linux_kernel >= 6.7, < 6.12.82'
  - 'linux_kernel >= 6.13, < 6.18.23'
  - 'linux_kernel >= 6.19, < 6.19.13'
  - linux_kernel = 3.2
  - linux_kernel = 7.0
patched:
  - linux_kernel 6.19.13
published: '2026-04-24'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T02:19:14.773'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-31649'
references:
  - url: 'https://git.kernel.org/stable/c/10d12b9240ebf96c785f0e2e4228318cd5f3a3eb'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/275bdf762e82082f064e60a92448fa2ac43cf95b'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/2c91b39912278d0878f9ba60ba04d2518b18a08d'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/513e06735f5be575b409d195822195348b164e48'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/51f4e090b9f87b40c21b6daadb5c06e6c0a07b67'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/6fca757c20396dc2e604dcc61922264e9e3dc803'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/a2b68a9a476b9544ff31f1fbcd5d80867a8a5e2f'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/b7b8012193fd98236d7ae05d4b553f010a77b2ef'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-019113.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-082556.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-457936.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-31649.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-31649'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2461551'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-31649'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-31649'
  - url: >-
      https://lore.kernel.org/linux-cve-announce/2026042459-CVE-2026-31649-b45c@gregkh/T
tags:
  - nvd
  - cve.org
  - csaf
  - vex
  - red-hat
  - score-dispute
epss: 0.00459
epssPercentile: 0.39579
ingestedAt: '2026-09-08T15:33:26.990Z'
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: total
  timestamp: '2026-10-16T15:11:32.382744Z'
scores:
  nvd: 9.8
  vendor: 6
  cna: 9.8
---

## Overview

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

net: stmmac: fix integer underflow in chain mode

The jumbo_frm() chain-mode implementation unconditionally computes

    len = nopaged_len - bmax;

where nopaged_len = skb_headlen(skb) (linear bytes only) and bmax is
BUF_SIZE_8KiB or BUF_SIZE_2KiB.  However, the caller stmmac_xmit()
decides to invoke jumbo_frm() based on skb->len (total length including
page fragments):

    is_jumbo = stmmac_is_jumbo_frm(priv, skb->len, enh_desc);

When a packet has a small linear portion (nopaged_len <= bmax) but a
large total length due to page fragments (skb->len > bmax), the
subtraction wraps as an unsigned integer, producing a huge len value
(~0xFFFFxxxx).  This causes the while (len != 0) loop to execute
hundreds of thousands of iterations, passing skb->data + bmax * i
pointers far beyond the skb buffer to dma_map_single().  On IOMMU-less
SoCs (the typical deployment for stmmac), this maps arbitrary kernel
memory to the DMA engine, constituting a kernel memory disclosure and
potential memory corruption from hardware.

Fix this by introducing a buf_len local variable clamped to
min(nopaged_len, bmax).  Computing len = nopaged_len - buf_len is then
always safe: it is zero when the linear portion fits within a single
descriptor, causing the while (len != 0) loop to be skipped naturally,
and the fragment loop in stmmac_xmit() handles page fragments afterward.

## Affected

- `linux_kernel >= 3.2.1, < 5.10.253`
- `linux_kernel >= 5.11, < 5.15.203`
- `linux_kernel >= 5.16, < 6.1.169`
- `linux_kernel >= 6.2, < 6.6.135`
- `linux_kernel >= 6.7, < 6.12.82`
- `linux_kernel >= 6.13, < 6.18.23`
- `linux_kernel >= 6.19, < 6.19.13`
- `linux_kernel = 3.2`
- `linux_kernel = 7.0`

## Remediation

Upgrade past the affected range:

- `linux_kernel 6.19.13`

## Vendor advisories

- **Red Hat VEX** · Moderate · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9 · no fix planned: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9 · updated 2026-10-16 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-31649.json)