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Fencer Vulns
high 7.5

CVE-2026-46110 json

net: stmmac: Prevent NULL deref when RX memory exhausted

published 2026-05-28 5 mo ago modified 2026-10-15 25 d ago also EUVD-2026-32869

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 43%
public exploits
0
none known

Summary

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

net: stmmac: Prevent NULL deref when RX memory exhausted

The CPU receives frames from the MAC through conventional DMA: the CPU allocates buffers for the MAC, then the MAC fills them and returns ownership to the CPU. For each hardware RX queue, the CPU and MAC coordinate through a shared ring array of DMA descriptors: one descriptor per DMA buffer. Each descriptor includes the buffer's physical address and a status flag ("OWN") indicating which side owns the buffer: OWN=0 for CPU, OWN=1 for MAC. The CPU is only allowed to set the flag and the MAC is only allowed to clear it, and both must move through the ring in sequence: thus the ring is used for both "submissions" and "completions."

In the stmmac driver, stmmac_rx() bookmarks its position in the ring with the `cur_rx` index. The main receive loop in that function checks for rx_descs[cur_rx].own=0, gives the corresponding buffer to the network stack (NULLing the pointer), and increments `cur_rx` modulo the ring size. After the loop exits, stmmac_rx_refill(), which bookmarks its position with `dirty_rx`, allocates fresh buffers and rearms the descriptors (setting OWN=1). If it fails any allocation, it simply stops early (leaving OWN=0) and will retry where it left off when next called.

This means descriptors have a three-stage lifecycle (terms my own): - `empty` (OWN=1, buffer valid) - `full` (OWN=0, buffer valid and populated) - `dirty` (OWN=0, buffer NULL)

But because stmmac_rx() only checks OWN, it confuses `full`/`dirty`. In the past (see 'Fixes:'), there was a bug where the loop could cycle `cur_rx` all the way back to the first descriptor it dirtied, resulting in a NULL dereference when mistaken for `full`. The aforementioned commit resolved that *specific* failure by capping the loop's iteration limit at `dma_rx_size - 1`, but this is only a partial fix: if the previous stmmac_rx_refill() didn't complete, then there are leftover `dirty` descriptors that the loop might encounter without needing to cycle fully around. The current code therefore panics (see 'Closes:') when stmmac_rx_refill() is memory-starved long enough for `cur_rx` to catch up to `dirty_rx`.

Fix this by explicitly checking, before advancing `cur_rx`, if the next entry is dirty; exit the loop if so. This prevents processing of the final, used descriptor until stmmac_rx_refill() succeeds, but fully prevents the `cur_rx == dirty_rx` ambiguity as the previous bugfix intended: so remove the clamp as well. Since stmmac_rx_zc() is a copy-paste-and-tweak of stmmac_rx() and the code structure is identical, any fix to stmmac_rx() will also need a corresponding fix for stmmac_rx_zc(). Therefore, apply the same check there.

In stmmac_rx() (not stmmac_rx_zc()), a related bug remains: after the MAC sets OWN=0 on the final descriptor, it will be unable to send any further DMA-complete IRQs until it's given more `empty` descriptors. Currently, the driver simply *hopes* that the next stmmac_rx_refill() succeeds, risking an indefinite stall of the receive process if not. But this is not a regression, so it can be addressed in a future change.

Patch / fix

  • Linux Linux 6.1.176, 6.6, 6.6.140, 6.12.88, 6.18.30, 7.0.7, 7.1
  • linux Debian 12 6.1.176-1
  • linux Debian 13 6.12.88-1
  • linux Debian 14 7.0.7-1

debian advisories DEBIAN-CVE-2026-46110

  • linux Ubuntu 24.04 LTS 6.8.0-136.136
  • linux Ubuntu 26.04 LTS 7.0.0-28.28
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1061.64
  • linux-aws Ubuntu 26.04 LTS 7.0.0-1009.9
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1064.72
  • linux-gcp Ubuntu 26.04 LTS 7.0.0-1008.8
  • linux-gke Ubuntu 24.04 LTS 6.8.0-1059.67
  • linux-gke Ubuntu 26.04 LTS 7.0.0-1003.4

ubuntu advisories UBUNTU-CVE-2026-46110

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel-rt Linux Micro 6.1, Linux Micro 6.0 6.4.0-48.1
  • kernel-source-rt Linux Micro 6.1, Linux Micro 6.0 6.4.0-48.1
  • kernel-rt Real Time Module 15 SP7 6.4.0-150700.7.59.2
  • kernel-syms-rt Real Time Module 15 SP7 6.4.0-150700.7.59.1
  • kernel-source-rt Real Time Module 15 SP7 6.4.0-150700.7.59.2
  • kernel-64kb SLE Module for Basesystem 15 SP7 6.4.0-150700.53.60.1
  • kernel-syms SLE Module for Development Tools 15 SP7 6.4.0-150700.53.60.1
  • kernel-azure SLE Module for Public Cloud 15 SP7 6.4.0-150700.53.60.1

suse advisories SUSE-SU-2026:22433-1SUSE-SU-2026:22458-1SUSE-SU-2026:2591-1SUSE-SU-2026:2482-1SUSE-SU-2026:22108-1SUSE-SU-2026:22137-1

  • kernel-source openSUSE Tumbleweed 7.0.11-1.1

opensuse advisories openSUSE-SU-2026:10954-1

  • kernel Azure Linux 3.0 6.6.141.1-1

azure linux advisories AZL-89016

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-46110 updated

kernel: net: stmmac: Prevent NULL deref when RX memory exhausted

  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more Red Hat Enterprise Linux 10 kernel
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

cisa ICSA-26-295-16 updated cvss 7.5

Siemens SIMATIC S7-1500 TM MFP

  • Siemens SIMATIC S7-1500 TM MFP - GNU/Linux subsystem
    affected: mitigation, no fix available

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

Exploit prediction

0.51% chance of exploitation in the next 30 days, higher than 43% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Linux Linux
  • Siemens SIMATIC S7-1500 TM MFP - GNU/Linux subsystem

Classification

Weakness
Technology feeds

References

Sources

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