[CVE-2026-98237][LOW] net: wwan: mhi_wwan_mbim: guard against a cyclic NDP chain

[CVE-2026-98237][LOW] net: wwan: mhi_wwan_mbim: guard against a cyclic NDP chain

[AL-KERNEL]

CVE: CVE-2026-98237
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: net: wwan: mhi_wwan_mbim: guard against a cyclic NDP chain
Commit: 3ed36ee1b29b028f6bc2ebe100152f61a33df05a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3ed36ee1b29b028f6bc2ebe100152f61a33df05a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98237
Analysis date: Fri, 09 Oct 2026 12:39:16 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-98237 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98237

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: LOW
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-2026-98237	LOW	https://www.kernelcve.org/list/?q=CVE-2026-98237 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT LOW AEGIS_AS=1 LEGACY=LOW RESULT=SAME (legacy and Aegis reconciliation agree; DECISION: both LOW)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';*CWE-835;*CWE-20;**CWE-400;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.6';DESCR 'The MHI WWAN MBIM receive path can enter an infinite loop because NDP traversal previously accepted a next offset that points to the current or an earlier NDP. A malformed NTB supplied by a malicious or compromised modem can keep mhi_mbim_rx running forever, pin one CPU at 100 percent, and prevent the receive thread from returning. For the CVSS the PR:N value is used because the triggering data can originate from the attached modem without a local user account or local code execution on the host. The realistic attack boundary is the physical or virtual MHI device rather than an arbitrary Internet peer because ordinary network traffic does not normally control the NDP metadata produced by modem firmware. The demonstrated impact is denial of service through CPU exhaustion. There is no supported UAF, out of bounds access, information leak, or write primitive, so confidentiality and integrity remain unaffected.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	MAYBE	SIMPLEFIX NETWORK HARDWARE LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2.
* Conservative score: 2.
* Raw paranoid score: 2.
* Paranoid score: 2.
* No floor or cap changed either score.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Firmware-mediated external influence. A malformed NTB generated or supplied by a malicious, compromised, or emulated modem reaches `mhi_mbim_rx()`.
* +1 Strong device-path DoS. The supplied test demonstrates an infinite kernel loop, one CPU pinned at 100 percent, and a receive thread that never returns.
* No extra Availability point. CPU consumption and the stuck receive path are the same demonstrated consequence.
* No direct remote-reachability bonus. An arbitrary network peer is not shown to control MBIM NDP metadata without modem or firmware mediation.
* No memory-corruption bonus. The patch establishes no OOB access, UAF, overwrite, stale pointer, or invalid free.
* No B5-R promotion. There is no heap OOB write, retry-accumulated write index, or later consumption of corrupted structured state.
* No confidentiality, integrity, LPE, controlled-reclaim, or arbitrary-write signals.
* No hardware rarity penalty. The path requires MHI WWAN functionality, but the supplied evidence does not establish rare physical-only hardware, and the behavior was also verified under QEMU.
* No privilege penalty. Host-admin privilege is not part of the vulnerable receive operation.

3. Reachability analysis

The immediate input producer is an attached, compromised, malicious, or emulated MHI modem capable of supplying an NTB with a cyclic NDP chain. This establishes below-host-admin triggering at the device boundary, so `HostAdminRequired=NO`, but it does not establish direct Internet reachability.

Ordinary cellular traffic is not shown to control `wNextNdpIndex`, because that structural metadata is normally produced by modem firmware. No network-namespace capability participates in the trigger, so `NamespaceScopedPrivilege=NO`. An MHI WWAN device or equivalent virtual setup and the affected driver are prerequisites. There is no race or narrow timing requirement. A single self-reference deterministically sustains the loop.

4. Primitive and severity interpretation

The exact primitive is attacker-influenced invalid traversal state causing a non-terminating loop. It is neither stale storage nor an active structured-object UAF. No release, refcount mutation, OOB write, descriptor corruption, or post-corruption operation is present.

This is `CLASS_C` because the demonstrated behavior is a deterministic CPU and receive-thread DoS without an independently useful corruption primitive. The practical consequence is loss of one CPU and failure of the affected receive path. A wider host impact through watchdog policy is possible operationally, but it does not create a separate scored primitive.

`ImportantCandidate=NO` because the B5-R requirements fail at the first gate and no memory-corruption or security-boundary primitive exists. `AutoDowngradeAllowed=YES` because automatic Moderate or Low-like handling would not discard unresolved corruption leverage.

5. One-sentence report phrase

A malformed cyclic NDP chain supplied through an MHI modem can keep `mhi_mbim_rx()` spinning indefinitely, pinning one CPU and blocking the receive thread without establishing memory corruption or direct network reachability.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The issue is a well-defined firmware-mediated infinite-loop DoS with a direct termination fix and no evidence of OOB access, UAF, corrupted-state consumption, authorization bypass, or privilege escalation.

7. Call-site confidence

Call-site confidence: high

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

Patch: net: wwan: mhi_wwan_mbim: guard against a cyclic NDP chain
Commit: 3ed36ee1b29b028f6bc2ebe100152f61a33df05a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3ed36ee1b29b028f6bc2ebe100152f61a33df05a

Commit description:

The NDP traversal in mhi_mbim_rx() only stops when wNextNdpIndex is
zero.  Nothing requires the offsets to advance, so a modem that
points an NDP at itself, or at an earlier NDP, keeps the loop
spinning forever on one CPU.

Break out when the next NDP offset is not larger than the current
one.

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 feeding the driver's
receive callback an NTB whose single NDP points at itself: the
unpatched driver spins in mhi_mbim_rx() with one CPU pinned at 100%
and the thread never returns.  With this check the loop terminates
within one iteration.

Changes in v2: move the non-increasing check to the wNextNdpIndex
retrieval site, as suggested by Loic Poulain, instead of tracking
the previous offset in a separate variable.

Link: https://patch.msgid.link/20260911021734.1396599-1-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=3ed36ee1b29b028f6bc2ebe100152f61a33df05a

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

The original Linux kernel CVE announcement for CVE-2026-98237 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98237

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:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.6

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: 2

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).