[CVE-2026-46151][MODERATE REGULAR] usb: usblp: fix heap leak in IEEE 1284 device ID via short response

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-46151
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: usb: usblp: fix heap leak in IEEE 1284 device ID via short response
Commit: 6e29c32a27218f2dcd4a4e9b0b3c5e7728640698
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6e29c32a27218f2dcd4a4e9b0b3c5e7728640698
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46151
Analysis date: Thu, 28 May 2026 12:15:54 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
A malformed USB printer can return a short IEEE 1284 device ID response with a large claimed length, causing `usblp` to expose stale kernel heap bytes through sysfs or ioctl.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-46151 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46151

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-46151	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N';*CWE-457;*CWE-200;CWE-908;CWE-665;Other CVSS 'AV:P/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N';BEST CVSS score: '4.7';DESCR 'usblp cached the IEEE 1284 device ID in a kmalloc buffer and trusted the two byte length prefix even when the USB control transfer completed short. A malicious or malformed USB printer can return only the length prefix and cause the driver to expose stale heap bytes through the ieee1284_id sysfs attribute or the IOCNR_GET_DEVICE_ID ioctl. For the CVSS the PR:L is used for the paranoid score because a local user needs access to the usblp device node or sysfs data path, or an equivalent USB passthrough context. The main attack model is physical or local USB device access, not network reachability. Impact is kernel information disclosure only, up to roughly 1021 bytes per affected ID read, with no supported write primitive or privilege escalation path.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 3) 	MAYBE	USB LEAK HARDWARE LINUS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Borderline, manual review recommended**::

## 2. Signal breakdown

Conservative signals:

* Confidentiality impact plausible: +1. Up to about 1021 bytes of stale kernel heap can be exposed.
* Local user/device access trigger: +1. A local user can read the sysfs attribute or use the ioctl if they have access to the device path.

Paranoid additional signal:

* Physical or USB passthrough attacker influence: +1. A malicious USB printer can choose the claimed length and cause the short response condition.

Limiting factors:

* Physical/local USB condition: -2. The primary attacker model requires malicious hardware or USB passthrough.
* No memory corruption.
* No write primitive.
* No privilege escalation.
* No network reachability.

## 3. Reachability analysis

The bug requires a malformed USB printer that completes the IEEE 1284 device ID request short while claiming a larger length. The leaked data is exposed locally through `ieee1284_id` sysfs or the `IOCNR_GET_DEVICE_ID` ioctl.

A local unprivileged user may need permissions to read the relevant sysfs attribute or open the `usblp` device node. In VM/container setups, USB passthrough can make a guest or container attacker relevant if they can attach or emulate the printer.

## 4. Severity interpretation

This is a borderline Moderate information disclosure issue. It is more significant than a one-byte status leak because the leak can be up to roughly 1021 bytes.

It is not an Important memory-corruption issue. The patch supports information disclosure only, with no arbitrary write, UAF, or LPE path.

## 5. One-sentence report phrase

A malformed USB printer can return a short IEEE 1284 device ID response with a large claimed length, causing `usblp` to expose stale kernel heap bytes through sysfs or ioctl.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Review is recommended where untrusted USB devices or USB passthrough are in scope. Otherwise this remains a physical/local USB information leak with no memory corruption or privilege escalation.

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

Patch: usb: usblp: fix heap leak in IEEE 1284 device ID via short response
Commit: 6e29c32a27218f2dcd4a4e9b0b3c5e7728640698
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6e29c32a27218f2dcd4a4e9b0b3c5e7728640698

Commit description:

usblp_ctrl_msg() collapses the usb_control_msg() return value to
0/-errno, discarding the actual number of bytes transferred.  A broken
printer can complete the GET_DEVICE_ID control transfer short and the
driver has no way to know.

usblp_cache_device_id_string() reads the 2-byte big-endian length prefix
from the response and trusts it (clamped only to the buffer bounds).
The buffer is kmalloc(1024) at probe time. A device that sends exactly
two bytes (e.g. 0x03 0xFF, claiming a 1023-byte ID) leaves
device_id_string[2..1022] holding stale kmalloc heap.

That stale data is then exposed:
  - via the ieee1284_id sysfs attribute (sprintf("%s", buf+2), truncated
    at the first NUL in the stale heap), and
  - via the IOCNR_GET_DEVICE_ID ioctl, which copy_to_user()s the full
    claimed length regardless of NULs, up to 1021 bytes of uninitialized
    heap, with the leak size chosen by the device.

Fix this up by just zapping the buffer with zeros before each request
sent to the device.

Cc: Pete Zaitcev <zaitcev@redhat.com>
Assisted-by: gkh_clanker_t1000
Cc: stable <stable@kernel.org>
Link: https://patch.msgid.link/2026042002-unicorn-greedily-3c63@gregkh
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/usb/class/usblp.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=6e29c32a27218f2dcd4a4e9b0b3c5e7728640698

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

The original Linux kernel CVE announcement for CVE-2026-46151 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46151

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:L/UI:N/S:U/C:H/I:N/A:N
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
  The Best / paranoid CVSS score: 4.7

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: 2
  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).