[CVE-2026-80825][MODERATE 7.0] wifi: mt76: mt7925: ensure tx headroom in usb_sdio_tx_prepare_skb

[CVE-2026-80825][MODERATE 7.0] wifi: mt76: mt7925: ensure tx headroom in usb_sdio_tx_prepare_skb

[AL-KERNEL]

CVE: CVE-2026-80825
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: wifi: mt76: mt7925: ensure tx headroom in usb_sdio_tx_prepare_skb
Commit: 9a72b180f0575e41471e088e09bddc4b73d6dee2
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9a72b180f0575e41471e088e09bddc4b73d6dee2
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80825
Analysis date: Fri, 04 Sep 2026 15:29:32 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: NO

Summary:
No one-sentence report phrase was found.

======================================================================
ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-80825 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80825

The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.

The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.

Published priority for this report: MODERATE 7.0
Manual review required: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-80825	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-80825 CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';CWE-124;*CWE-787;*CWE-20;CWE-754;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.5';DESCR 'An skb headroom bug in the mt7925 USB/SDIO transmit path can trigger skb_under_panic when a forwarded bridged frame is transmitted through an mt7925u AP. Locally generated traffic usually has reserved extra_tx_headroom, but frames forwarded through ieee80211_8023_xmit may arrive without enough headroom for the TX descriptor and USB/SDIO header. A network adjacent host on the bridged LAN or Wi-Fi segment can trigger a kernel BUG and crash the system by causing such a frame to be forwarded. For the CVSS the PR:N is used because no local account on the victim is needed when the attacker can send traffic into the affected L2 segment. The attack is not generally Internet reachable and depends on a specific mt7925 USB/SDIO AP bridge setup and ingress driver headroom behavior. Impact is denial of service via kernel crash only, with no supported privilege escalation or information disclosure primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	REMOTE DANGER NETWORK SKB TEST KPANIC 	YES	NO	checked

======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=5
ActionableScoreLower=4

1. ActionableScore
* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

2. Signal breakdown
* Remote reachable / network-triggerable: +2. A host on the bridged LAN or Wi-Fi segment can trigger the crash by causing a forwarded frame to traverse the mt7925u AP TX path. This is network-adjacent rather than Internet-wide, but no local account on the victim is needed.
* Memory layout invariant restoration: +1. The patch restores the required skb headroom invariant before pushing the TX descriptor and USB/SDIO header.
* Reliable kernel crash / strong DoS: +1. The commit shows skb_under_panic and kernel BUG from skb_push when headroom is insufficient.
* Availability impact realistic: +1 in paranoid scoring only. In an affected bridge/AP setup, the first short forwarded frame can panic the kernel, making the DoS practical and system-wide.
* Rare AND difficult-to-reach subsystem/configuration: -1. The bug requires mt7925 USB/SDIO AP bridging plus an ingress path that leaves insufficient skb headroom.
* No generic memory corruption bonus. The observed failure is caught by skb_under_panic before a demonstrated attacker-controlled overwrite primitive.

3. Reachability analysis
The attacker can be a network-adjacent host able to send traffic into the bridged LAN or Wi-Fi segment. No local Linux user account on the victim is required, so PR:N is reasonable for CVSS-style reasoning. The path is not generally Internet reachable and depends on a specific deployment: mt7925u or related mt7925 USB/SDIO device operating as an AP with bridging from another interface. Namespaces and containers are not central to exploitation because the trigger is packet forwarding through the physical wireless device. Realistic exploitation is credible on affected router/AP setups, but exposure is hardware and topology dependent.

4. Severity interpretation
This behaves like an actionable Moderate network-adjacent DoS, not an Important LPE candidate. The bug is in skb headroom handling, but the provided evidence supports a kernel BUG/panic rather than a usable underwrite, UAF, type confusion, or privilege escalation primitive. The paranoid score is higher because the crash can be triggered remotely from the local L2 segment in vulnerable bridge/AP deployments, but the issue should not be upgraded to memory-corruption-based Important without evidence that skb_under_panic can be bypassed or converted into controlled corruption.

5. One-sentence report phrase
An skb headroom bug in the mt7925 USB/SDIO TX path allows a network-adjacent host on a bridged LAN or Wi-Fi segment to trigger skb_under_panic and crash the kernel when forwarded frames lack space for the TX descriptor and USB/SDIO header.

6. Manual review recommendation
YES REQUIRES MANUAL CHECK. The issue is network-adjacent and can remotely crash affected AP/bridge deployments, but it appears to be DoS-only and hardware/topology dependent rather than a demonstrated privilege escalation primitive.

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: wifi: mt76: mt7925: ensure tx headroom in usb_sdio_tx_prepare_skb
Commit: 9a72b180f0575e41471e088e09bddc4b73d6dee2
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9a72b180f0575e41471e088e09bddc4b73d6dee2

Commit description:

mt7925_usb_sdio_tx_prepare_skb() pushes a TX descriptor and a USB
header onto every skb and assumes the headroom for them is already
there. That holds for locally generated traffic, where mac80211
reserves hw->extra_tx_headroom, but forwarded frames are sent through
ieee80211_8023_xmit(), which does not reserve it. Bridge a wired
interface to an mt7925u AP and the first forwarded frame that arrives
short panics the kernel:

 skbuff: skb_under_panic: len:415 put:4 tail:0x19b end:0x640 dev:wlan1
 kernel BUG at net/core/skbuff.c:212!
 Call trace:
  skb_panic+0x58/0x60 (P)
  skb_push+0x58/0x60
  mt7925_usb_sdio_tx_prepare_skb+0xf8/0x1b8 [mt7925_common]
  mt76u_tx_queue_skb+0xa0/0x1f8 [mt76_usb]
  __mt76_tx_queue_skb+0x54/0xe8 [mt76]
  mt76_txq_schedule.part.0+0x204/0x478 [mt76]
  mt76_txq_schedule_all+0x50/0x80 [mt76]
  mt792x_tx_worker+0x68/0x100 [mt792x_lib]
  __mt76_worker_fn+0x84/0x150 [mt76]

Whether a given setup hits it depends on how much headroom the ingress
netdev leaves in its rx skbs. Reproduced on a Raspberry Pi 5 bridging
onboard ethernet to a Netgear A9000; originally reported on an MT7986
router running OpenWrt. Nick Morrow's testing on a Pi 4 (bcmgenet),
which leaves more headroom, helped narrow the trigger to the ingress
path.

The same bug was fixed on mt7921 by commit 98c4d0a ("mt76:
mt7921: don't assume adequate headroom for SDIO headers"), but mt7925
was copied from mt7921 without the fix. Add the same guard here.

Fixes: c948b5d ("wifi: mt76: mt7925: add Mediatek Wi-Fi7 driver for mt7925 chips")
Cc: stable@vger.kernel.org
Link: morrownr/mt76#52
Signed-off-by: Devin Wittmayer <lucid_duck@justthetip.ca>
Link: https://patch.msgid.link/20260715023348.59506-1-lucid_duck@justthetip.ca
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/core/skbuff.c
  drivers/net/wireless/mediatek/mt76/mt7925/mac.c

Diff excerpt:

Not included in this email. See the upstream URL for the full patch.

Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9a72b180f0575e41471e088e09bddc4b73d6dee2

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-80825 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80825

The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.

The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.

The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.

Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:

  Conservative CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 6.5

The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.

CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.

A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.

  Conservative ActionableScore: 4
  Paranoid ActionableScore: 5

The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.

For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:

  ActionableScore below 5   -> MODERATE REGULAR
  ActionableScore 5 or more -> MODERATE 7.0

The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.

There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).

KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.

AL-KERNEL base severity for this report: MODERATE
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): MODERATE 7.0

These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).

Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).