[CVE-2026-98236][MODERATE REGULAR] net: wwan: mhi_wwan_mbim: check skb_copy_bits() return value

[CVE-2026-98236][MODERATE REGULAR] net: wwan: mhi_wwan_mbim: check skb_copy_bits() return value

[AL-KERNEL]

CVE: CVE-2026-98236
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net: wwan: mhi_wwan_mbim: check skb_copy_bits() return value
Commit: 650af68435eaee783824457d2ef78cc5c03c1e88
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=650af68435eaee783824457d2ef78cc5c03c1e88
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98236
Analysis date: Fri, 09 Oct 2026 12:21:03 -0400
ActionableScore: 3
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-98236 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98236

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 REGULAR
Manual review required: YES

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

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

CVE-2026-98236	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98236 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE RESULT=DIFF (independent Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N';CWE-252;*CWE-457;*CWE-200;CWE-908;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '5.3';DESCR 'An unchecked skb_copy_bits failure in mhi_mbim_rx can cause a newly allocated skb with uninitialized kernel heap contents to be passed into the network stack. A modem can trigger the issue by supplying a DPE whose datagram range lies outside the received skb even though it appears to remain inside the declared NTB. If the uninitialized first byte resembles IPv4 or IPv6, the skb can reach netif_rx and may expose kernel heap data to local packet consumers or further network processing. For the CVSS the PR:N is selected because an attacker controlling the MHI modem data source does not need a Linux user account or privileges on the victim. The confirmed attack boundary is the attached modem or emulated device rather than an arbitrary remote Internet host. A network adjacent scenario is plausible only if an attacker can influence or compromise the modem through the cellular or device environment, so AC:H is used for the paranoid assessment. Impact is primarily confidentiality loss. No UAF, out of bounds write, arbitrary write, or reliable privilege escalation primitive is shown.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	MAYBE	SIMPLEFIX LEAK NETWORK SKB LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

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

ActionableScore=3
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 3
* Raw paranoid score: 3
* Paranoid score: 3
* No floor or cap was applied.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +1 Firmware-mediated external influence. A modem controls the DPE offset and length, but firmware or device mediation prevents classification as directly remote.
* +1 Confidentiality plausible. Failed copying leaves uninitialized heap bytes in `skbn`, which can be submitted to `netif_rx()` and become visible to packet consumers.
* +1 Common networking receive path. When the uninitialized first nibble resembles IPv4 or IPv6, the buffer enters the ordinary network receive stack.
* No OOB-write point. `skb_copy_bits()` rejects the invalid source range rather than writing beyond `skbn`.
* No B5-R promotion. There is no confirmed heap OOB write, retry-accumulated offset, or later consumption of state corrupted by such a write.
* No direct-remote point. Control of network traffic alone is not shown to provide control over the modem-generated DPE.
* No strong disclosure or Class A point. The patch confirms uninitialized data entering the network stack, but does not establish reliable attacker read-back, a selected victim allocation, or disclosure of specific protected data.
* No integrity, crash, UAF, arbitrary-write, controlled-reclaim, or privilege-escalation points.

3. Reachability analysis

The confirmed trigger originates from a modem or emulated MHI device that supplies a DPE range outside the received skb. Such a device does not require host-administrator credentials to deliver RX metadata, so `HostAdminRequired=NO`.

The supplied evidence does not show that an arbitrary cellular-network peer can directly construct the affected host-side DPE. Firmware compromise, malicious device behavior, fault injection, or an equivalent modem-control condition remains material. No user or network namespace capability participates in the vulnerable receive path, so `NamespaceScopedPrivilege=NO`.

No race or retry sequence is involved. Required hardware is MHI MBIM WWAN functionality, but no rare-hardware penalty is applied merely because this is a driver path.

4. Primitive and severity interpretation

The exact primitive is consumption of uninitialized heap contents after an ignored `skb_copy_bits()` failure. The destination allocation itself is correctly sized, and the invalid source range causes copying to fail rather than producing an OOB write.

This is neither a UAF nor a lifetime violation. It is classified as Class C because the concrete result is an invalid skb containing uninitialized bytes, while a reliable attacker-readable disclosure sink is not fully established. The data can progress beyond the driver if its first nibble happens to select IPv4 or IPv6, but the attacker is not shown to control those uninitialized bytes.

The demonstrated security consequence is potential kernel-heap disclosure into packet-processing paths. Reliable disclosure to the modem, an unprivileged local process, or an external peer remains unproven. Therefore this is not an Important candidate, but manual review is recommended to determine actual packet observability and forwarding behavior in affected deployments. Automatic downgrade remains allowed because no strong corruption, lifetime, authorization, or confirmed substantial disclosure primitive is established.

5. One-sentence report phrase

An attacker controlling an MHI MBIM modem can cause an skb containing uninitialized kernel heap data to enter the network receive path, creating a potential information disclosure whose final observability depends on packet parsing and deployment configuration.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm whether accepted IPv4 or IPv6-looking buffers can be captured by local consumers, forwarded externally, or observed by the modem in realistic configurations.

7. Call-site confidence

Call-site confidence: medium

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

Patch: net: wwan: mhi_wwan_mbim: check skb_copy_bits() return value
Commit: 650af68435eaee783824457d2ef78cc5c03c1e88
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=650af68435eaee783824457d2ef78cc5c03c1e88

Commit description:

mhi_mbim_rx() ignores the return value of skb_copy_bits() when it
copies each datagram out of the NTB.  The datagram offset and length
come from the DPE, which is only checked to lie within the NTB
itself, so a modem can point a datagram outside the received skb.
The copy then fails and the freshly allocated skbn is passed to
netif_rx() with its uninitialized contents still in place, leaking
kernel heap memory into the network stack.

Free the skb and account an error when the copy fails.

Fixes: aa730a9 ("net: wwan: Add MHI MBIM network driver")
Cc: stable@vger.kernel.org
Suggested-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
Signed-off-by: Guanglei Zhu <zhugl3@xiaopeng.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Verified in a QEMU guest with a fault injector pointing a DPE
outside the received NTB: the copy fails, and the unpatched driver
hands the uninitialized skbn to the network stack (observed as
"unknown protocol" on bytes that were never written).  With this
check the failed datagram is dropped and counted as an rx error.

Changes in v2: factor the free-and-count sequence out into
mhi_mbim_rx_drop(), shared with the unknown-protocol path, as
suggested by Loic Poulain.

Link: https://patch.msgid.link/20260911021734.1396599-2-zhugl3@xiaopeng.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Changed files:
  drivers/net/wwan/mhi_wwan_mbim.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=650af68435eaee783824457d2ef78cc5c03c1e88

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

The original Linux kernel CVE announcement for CVE-2026-98236 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98236

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:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
  The Best / paranoid CVSS score: 5.3

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: unknown
  Paranoid ActionableScore: 3

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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).