[CVE-2026-74675][MODERATE 7.0] vt: stabilize tty reference in kbd_keycode with tty_port_tty_get

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

CVE: CVE-2026-74675
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: vt: stabilize tty reference in kbd_keycode with tty_port_tty_get
Commit: b84fd400f80adf4d1c88fbce50ae1cf2f8119e65
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b84fd400f80adf4d1c88fbce50ae1cf2f8119e65
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74675
Analysis date: Sat, 22 Aug 2026 12:16:34 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A local race in the VT keyboard path can leave `kbd_keycode()` using a tty pointer without a held reference while `con_shutdown()` clears it, creating a stale pointer or UAF candidate that can crash the kernel and warrants manual review.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74675 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74675

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 7.0
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-2026-74675	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	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:H/A:H';CWE-362;*CWE-416;*CWE-672;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in the VT keyboard path can occur because kbd_keycode reads vc port tty without taking a tty reference while con_shutdown can clear the same pointer under a different lock. This creates a stale tty pointer window and can turn later tty access in kbd_keycode into a use after free candidate or crash. For the CVSS the PR:L is used because reliable triggering requires local code or local console control, such as activity that opens or closes VT tty state together with generated keyboard events. The issue is not network reachable. Impact is at least local denial of service via kernel crash and in the paranoid case may include confidentiality or integrity impact because the bug class is a race on a lifetime managed tty object.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	INIT PRINTF-TTY SIMPLEFIX IMPROVEONLY LINUS  INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1
  The bug is in the VT keyboard path and can plausibly be reached by a local user or local console context that can generate keyboard activity while tty teardown occurs.

* Memory corruption, weak or indirect corruption candidate: +1
  `kbd_keycode()` used `vc->port.tty` without taking a reference. If `con_shutdown()` clears or releases the tty concurrently, this creates a stale pointer window. No attacker controlled reclaim or overwrite primitive is shown.

* Real lifetime corruption: +1
  The patch explicitly fixes a missing lifetime reference by replacing the raw pointer read with `tty_port_tty_get()` and releasing it with `tty_kref_put()`.

* Reliable kernel crash or strong DoS concern: +1
  A stale tty pointer can plausibly lead to invalid dereference or use after free style crash in the keyboard path.

* Hard or unreliable race: -1
  Exploitation depends on a timing window between keyboard event handling and tty shutdown.

* Broad default subsystem exposure: +1
  VT and tty code are common kernel components, although practical reachability is local and often tied to console or tty permissions.

Paranoid adjustment:

* Paranoid score removes or weakens the timing penalty because keyboard events and tty teardown can potentially be repeated many times under local control. This raises the practical review score to 5, but the race UAF downgrade rule still prevents treating this as a strong LPE primitive without evidence of reclaim, overwrite, callback control, or type confusion.

## 3. Reachability analysis

The issue is local only and is not network reachable. A realistic trigger requires local code execution or local console control capable of interacting with VT tty state while keyboard events are processed. Namespaces do not obviously make this broadly reachable, because VT access is usually host local and constrained by device permissions. The path is common in kernels with virtual terminal support, but many server deployments have limited practical exposure because attackers usually do not control the physical console or VT devices.

Call-site confidence: medium. The patch shows the direct lifetime fix in `kbd_keycode()`, but the full teardown and caller paths are not included.

## 4. Severity interpretation

This behaves above ordinary Moderate because it is a real lifetime race on a referenced kernel object. Conservative handling should treat it as a local DoS and stale pointer issue, not as proven privilege escalation. Theoretical memory corruption potential exists because the stale pointer is a tty object pointer, but the patch does not show attacker controlled reclaim, write after free, type confusion, callback dispatch, or refcount takeover. Therefore the practical bucket is Actionable Moderate, with manual review recommended or required before auto closing.

## 5. One-sentence report phrase

A local race in the VT keyboard path can leave `kbd_keycode()` using a tty pointer without a held reference while `con_shutdown()` clears it, creating a stale pointer or UAF candidate that can crash the kernel and warrants manual review.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a real object lifetime race involving a tty reference. Even though the demonstrated impact is most defensibly local DoS, UAF style tty lifetime bugs should not be auto closed without checking whether any reachable path gives attacker controlled reuse, callback influence, or stronger corruption behavior.

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

Patch: vt: stabilize tty reference in kbd_keycode with tty_port_tty_get
Commit: b84fd400f80adf4d1c88fbce50ae1cf2f8119e65
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b84fd400f80adf4d1c88fbce50ae1cf2f8119e65

Commit description:

kbd_keycode() reads vc->port.tty without acquiring a tty reference,
racing against con_shutdown() which clears port.tty under a different
lock. Use tty_port_tty_get()/tty_kref_put() to hold a proper reference
for the duration the tty pointer is needed.

Assisted-by: AISLE:Snapshot
Signed-off-by: Joshua Rogers <linux@joshua.hu>
Cc: stable <stable@kernel.org>
Link: https://patch.msgid.link/20260731-tty-vt-stuff-v1-1-be99b9da8e30@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/tty/vt/keyboard.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=b84fd400f80adf4d1c88fbce50ae1cf2f8119e65

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

The original Linux kernel CVE announcement for CVE-2026-74675 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74675

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:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 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: 4
  Paranoid ActionableScore: 5

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 7.0

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).