[CVE-2026-80827][MODERATE REGULAR] USB: serial: option: fix slab OOB read in interrupt URB callback

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

CVE: CVE-2026-80827
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: USB: serial: option: fix slab OOB read in interrupt URB callback
Commit: fbe60fd2abc8a5561f39719a41ad9a01b5d8e567
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fbe60fd2abc8a5561f39719a41ad9a01b5d8e567
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80827
Analysis date: Fri, 04 Sep 2026 17:41:55 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like, manual review due kernel OOB read
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-80827 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80827

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-2026-80827	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-80827 CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H';CWE-125;*CWE-20;CWE-129;CWE-125;Other CVSS 'AV:P/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:L';BEST CVSS score: '5.4';DESCR 'A slab out-of-bounds read exists in the USB serial option interrupt URB callback because option_instat_callback can access data at offset sizeof(*req_pkt) without first proving that the completed URB contains that byte. A malicious or malformed USB device can declare an interrupt IN endpoint with wMaxPacketSize 8 and return a short or boundary sized packet, causing the driver to read one byte beyond the kmalloc-8 buffer. For the CVSS the PR:N because the attacker does not need software privileges on the victim when using a malicious USB device, but UI:R is required because the device must be attached or otherwise presented to the host. The issue is not directly network reachable in normal deployments and is mainly a physical or local device attack surface. Impact is at least limited confidentiality exposure from an invalid kernel read and possible denial of service on hardened or debug kernels. In the paranoid score, limited integrity impact is kept possible because the out-of-bounds byte is interpreted as modem signal state, but there is no evidence of an arbitrary write primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like, manual review due kernel OOB read (with actual score 2)	YES	READ OOB USB INIT PRINTF-TTY ERRORPATH HARDWARE LINUS PACKET  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	NO	NO	checked

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

ActionableScore=2
ActionableScoreLower=1

1. ActionableScore
* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like, manual review due kernel OOB read**::

2. Signal breakdown
* Confidentiality impact plausible: +1. The bug is a one byte slab OOB read from a kmalloc-8 interrupt URB buffer.
* Availability impact realistic: +1 in the paranoid score only. A crash is plausible mainly on hardened or debug kernels such as KASAN or panic-on-oops style configurations, but not strongly demonstrated as reliable on normal production kernels.
* Physical-only or rare hardware-only condition: -2. The realistic attacker is a malicious or malformed USB device, or an equivalent local USB device presentation path.
* Weak corruption only: +0. This is a read-only OOB access. There is no OOB write, UAF, double free, type confusion, callback overwrite, or attacker-controlled reclaim primitive shown.

3. Reachability analysis
A malicious USB device can trigger the bug by exposing an interrupt IN endpoint with wMaxPacketSize 8 and returning a short or boundary-sized packet that reaches option_instat_callback(). No software privileges on the victim are needed for the malicious-device model, but user interaction or physical/device presentation is required. This is not network reachable in normal deployments. The affected driver is old and widely available, but practical exposure depends on whether such a USB serial option device can be attached and bound to the driver.

4. Severity interpretation
This behaves like a low-end to ordinary Moderate kernel memory-safety issue. The theoretical issue is a slab OOB read with possible limited information exposure and possible crash under hardened/debug configurations. Realistic exploitation evidence is weak because the read is one byte, read-only, physically mediated, and does not show a stronger corruption or privilege-escalation primitive.

5. One-sentence report phrase
A slab OOB read in the USB serial option interrupt URB callback can be triggered by a malicious USB device with a small interrupt endpoint packet, causing limited kernel memory exposure and possible DoS on hardened systems.

6. Manual review recommendation
MANUAL CHECK REQUIRED. YES REQUIRES MANUAL CHECK. This is not an Important-class candidate by default, but it is still a kernel slab OOB read and should not be auto-closed without confirming product exposure to untrusted USB devices.

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

Patch: USB: serial: option: fix slab OOB read in interrupt URB callback
Commit: fbe60fd2abc8a5561f39719a41ad9a01b5d8e567
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fbe60fd2abc8a5561f39719a41ad9a01b5d8e567

Commit description:

The interrupt URB buffer is allocated in setup_port_interrupt_in() based
on the endpoint's wMaxPacketSize:

    buffer_size = usb_endpoint_maxp(epd);
    port->interrupt_in_buffer = kmalloc(buffer_size, GFP_KERNEL);

When a USB device declares wMaxPacketSize = 8 on its interrupt IN
endpoint, the buffer is allocated from kmalloc-8 cache (exactly
8 bytes).

If the device sends a short packet (actual_length < wMaxPacketSize),
the URB completes with status == 0 and the callback proceeds to read:

    data[sizeof(struct usb_ctrlrequest)]

which evaluates to data[8], accessing 1 byte beyond the allocated 8-byte
buffer. This results in a slab out-of-bounds read.

Fix this by adding the missing bounds check: first verify that the
actual length is large enough to contain the struct usb_ctrlrequest
header before accessing req_pkt->bRequestType and req_pkt->bRequest,
and then verify that there is an additional byte for the modem signal
state before reading data[sizeof(struct usb_ctrlrequest)] inside the
conditional.  Use sizeof(*req_pkt) instead of sizeof(struct
usb_ctrlrequest) for consistency.

Assisted-by: Claude:deepseek-v4-pro
Signed-off-by: Jiale Yao <yaojiale02@163.com>
Fixes: 58cfe91 ("[PATCH] USB: add Option Card driver")
Cc: stable@vger.kernel.org	# v2.6.12
[ johan: use dev_err(); split signals declaration and initialisation ]
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/usb/serial/option.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=fbe60fd2abc8a5561f39719a41ad9a01b5d8e567

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

The original Linux kernel CVE announcement for CVE-2026-80827 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80827

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:R/S:U/C:L/I:N/A:L
  The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.4

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: 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).