* [CVE-2026-90034][LOW] usb: image: mdc800: change kmalloc() to kzalloc()
@ 2026-09-16 13:55 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-16 13:55 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-90034
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: usb: image: mdc800: change kmalloc() to kzalloc()
Commit: 6c601410d1a9ae645f604fe2f61b9f4942c77dfb
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6c601410d1a9ae645f604fe2f61b9f4942c77dfb
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90034
Analysis date: Wed, 16 Sep 2026 09:55:06 -0400
ActionableScore: 2
ActionableScore lower bound: 1
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-2026-90034 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90034
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-2026-90034 LOW https://www.kernelcve.org/list/?q=CVE-2026-90034 CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N';CWE-908;*CWE-457;*CWE-200;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '3.3';DESCR 'The mdc800 USB image driver allocated receive buffers with kmalloc, leaving stale kernel memory in irq_urb_buffer or download_urb_buffer until overwritten by device data. If a short USB message is received in mdc800_usb_irq or mdc800_usb_download_notify, the unused tail of the buffer may remain uninitialized and could be exposed through the driver data path. For the CVSS the PR:L is used for the paranoid score because a local user with access to the mdc800 device node or a USB gadget setup may be able to observe data returned by the driver. The issue is not network reachable and normally requires physical USB access or local access to a USB attached device. Impact is limited to confidentiality exposure of small stale kernel memory contents. No direct integrity impact, availability impact, memory corruption, or privilege escalation primitive is indicated by the code change.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) YES USB SIMPLEFIX LEAK LINUS NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=2
ActionableScoreLower=1
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate**::
No floor or cap was applied.
2. Signal breakdown
Conservative signals:
* +1 Confidentiality plausible: kmalloc receive buffers may retain stale kernel memory, and a short USB message may leave part of irq_urb_buffer or download_urb_buffer uninitialized before later driver-visible processing.
* +1 Firmware or device mediated external influence: the short message comes from a USB device, so attacker influence is mediated through the attached device.
* -1 Legacy and specialized path: mdc800 is a legacy USB image driver and exploitation requires the driver and matching device path to be present.
Paranoid signals:
* +1 Confidentiality plausible: small stale kernel memory disclosure remains the only supported security impact.
* +1 Device or local device access reachability: a malicious attached USB device, or a local actor with access to the device path in some deployments, may trigger the short-message condition.
* No legacy penalty in the paranoid score because the evaluated deployment may already expose this device path.
Important non-awarded signals:
* No UAF or lifetime violation is established.
* No OOB write, arbitrary write, controlled corruption, or privilege escalation primitive is established.
* No integrity or availability impact is supported by the patch.
* No remote network reachability is established.
* No security-boundary or authorization bypass is established.
* No repeated release or refcount operation exists.
* No manual-review floor applies.
3. Reachability analysis
The most direct attacker model is a malicious or malformed USB device that sends shorter than expected messages to the mdc800 driver. This does not require host administrator privilege once the vulnerable driver path is reachable, but it does require physical USB access or an already attached device path. A second possible model is a local user who can interact with the mdc800 device node and observe data returned by the driver, but ordinary unprivileged reachability is not proven from the supplied patch alone.
No namespace-scoped capability is involved. There is no network trigger. Prior setup requires the driver to be built or loaded and the relevant USB device path to exist. The hardware path is specialized and legacy, but the bug itself is simple and not timing dependent.
4. Primitive and severity interpretation
The exact primitive is limited uninitialized kernel memory exposure from fixed receive buffers allocated with kmalloc instead of kzalloc. The affected storage is fixed driver buffer storage, not an active structured object and not a stale post-lifetime object. The demonstrated consequence is potential disclosure of a small amount of stale kernel memory if a short USB message leaves part of the buffer unchanged and that data becomes observable through the driver data path.
This is PrimitiveClass=NONE because no corruption, UAF, ownership violation, authorization bypass, or meaningful active-object primitive is established. The likely operational severity is Low to ordinary Moderate. ImportantCandidate=NO because the patch supports only limited confidentiality impact. AutoDowngradeAllowed=YES because there is no unresolved kernel corruption or boundary-bypass primitive.
5. One-sentence report phrase
The mdc800 USB image driver used kmalloc for receive buffers, so short USB messages could leave stale kernel memory in the buffer tail and potentially expose a small confidentiality leak through the driver path.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
Reason: this is a small uninitialized-memory disclosure in a legacy USB driver path with no UAF, corruption, crash, privilege escalation, or network exposure established.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: usb: image: mdc800: change kmalloc() to kzalloc()
Commit: 6c601410d1a9ae645f604fe2f61b9f4942c77dfb
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6c601410d1a9ae645f604fe2f61b9f4942c77dfb
Commit description:
Change the kmalloc() calls in usb_mdc800_init() for irq_urb_buffer and
download_urb_buffer to kzalloc(), avoiding potential stack leaks if a
shorter message is received in mdc800_usb_irq() and
mdc800_usb_download_notify()
Assisted-by: gkh_clanker_t1000
Cc: stable <[email protected]>
Signed-off-by: Griffin Kroah-Hartman <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
drivers/usb/image/mdc800.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=6c601410d1a9ae645f604fe2f61b9f4942c77dfb
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90034 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90034
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:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
The Best / paranoid CVSS score: 3.3
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: 1
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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