[CVE-2026-93134][MODERATE REGULAR] printk: Fix possible console use-after-free [ Upstream

[CVE-2026-93134][MODERATE REGULAR] printk: Fix possible console use-after-free [ Upstream

[AL-KERNEL]

CVE: CVE-2026-93134
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: printk: Fix possible console use-after-free [ Upstream
Commit: f0104a7b730de32eefb3d4a27279592b5504ad59
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f0104a7b730de32eefb3d4a27279592b5504ad59
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93134
Analysis date: Fri, 18 Sep 2026 02:26:34 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
A possible use-after-free in `console_flush_one_record()` can occur when legacy console handover releases the console SRCU read lock before later `con` access, leading primarily to a local kernel crash or DoS.

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

The original Linux kernel CVE announcement for CVE-2026-93134 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93134

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-2026-93134	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-93134 CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';*CWE-416;CWE-362;*CWE-672;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A possible use after free exists in console_flush_one_record() because the console pointer can be used after nbcon_legacy_emit_next_record() or console_emit_next_record() performs a handover and releases the console SRCU read lock. After that handover the struct console object may no longer be valid, but the old code could still read nbcon_seq_read(con) or con seq before checking the handover flag. For the CVSS the PR:L is used for the paranoid score because a local process may be able to generate printk activity or run in an environment with delegated console or driver control, while reliable triggering still depends on a race with console handover and console lifetime changes. The issue is not directly network reachable and is triggered through local kernel logging and console management paths. Impact is at least denial of service via kernel crash and in worst case may allow limited confidentiality or integrity impact due to a kernel use after free, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)  SKIP CVE-2026-93134 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	UAF IMPROVEONLY LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	-	-	checked

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

ActionableScore=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

## 1. ActionableScore

* Raw conservative score: 3
* Conservative score: 4
* Raw paranoid score: 4
* Paranoid score: 4
* Final recommended bucket: **Borderline / manual review recommended**::

Applied conservative floor: 3 -> 4 because a real post-lifetime console pointer use is established and host-admin-equivalent reachability is not positively established.

## 2. Signal breakdown

Positive signals:

* +2 Real UAF / lifetime violation: after `nbcon_legacy_emit_next_record()` or `console_emit_next_record()` performs a handover, the console SRCU read lock is released and `con` may no longer be valid, but the old code still used `con`.
* +1 Reliable kernel crash / strong DoS: dereferencing a possibly freed `struct console` through `nbcon_seq_read(con)` or `con->seq` can plausibly cause an Oops or kernel crash.
* +1 Broad/common subsystem exposure in paranoid scoring: printk and console flushing are core kernel paths and are broadly present, although the exact handover and console-lifetime race is narrower than ordinary printk usage.

Negative signals:

* -1 Conservative hard timing/lifetime race: the bug requires a specific ordering where legacy console handover releases SRCU protection before later `con` use, and invalidation of the console object must occur in that window.

Non-awarded material signals:

* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Information disclosure not demonstrated.
* Privilege escalation not demonstrated.
* Concrete repeated release/refcount mutation not present.
* Structured stale-object exploitation leverage not awarded because the stale use shown is a shallow sequence read, not consumption of attacker-controlled replacement fields, callbacks, ownership state, or security-sensitive pointers.
* Weak LPE not awarded solely because this is a UAF.
* Extra Availability not awarded because the same possible crash is already counted.
* Remote reachability not established.
* Namespace-scoped privilege not established.

Repeated release/refcount checklist:

* First release can end lifetime: not applicable as a direct release/put sequence is not shown.
* Exact same reference survives to second release: no.
* Second operation is lifetime/refcount mutation: no.
* Concrete repeated release/refcount +1 awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied: no.

## 3. Reachability analysis

The vulnerable path is in printk console flushing. An attacker or workload may be able to generate printk activity, but the dangerous condition also depends on a legacy printing handover and potential invalidation of the `struct console` after the SRCU read lock is released.

Below-host-admin reachability is not positively established from the supplied patch. Reliable triggering appears to depend on console lifetime changes, console handover behavior, or driver/device console unregister paths, which often involve privileged kernel/device management, but the supplied evidence does not prove that host-admin-equivalent privilege is always required. Therefore `HostAdminRequired=UNKNOWN`, not `YES`.

The issue is not network reachable. It is not namespace-scoped in any meaningful way because printk console registration, handover, and console lifetime are not per-network-namespace attacker-controlled objects.

No special hardware requirement is established beyond having affected console/printk paths. The timing condition is a real race-like lifetime window, but not enough is supplied to prove a repeatable unprivileged trigger.

## 4. Primitive and severity interpretation

The exact primitive is a post-SRCU lifetime use of `struct console *con` after a handover may have released the protection that made the pointer valid. This is a real lifetime violation and therefore `PrimitiveClass=CLASS_B`, with `RealUAF=YES`.

The stale object is an active structured kernel object, not a fixed DMA or URB buffer. However, the demonstrated stale use is limited to reading the console sequence state immediately after emit, not to invoking callbacks, using attacker-shaped replacement data, performing a second refcount mutation, or modifying security-sensitive state.

Demonstrated consequence is kernel crash or DoS. A stronger consequence such as information disclosure or privilege escalation is theoretically possible for some UAF classes, but no controlled reclaim, attacker-directed replacement, arbitrary read/write, callback control, or security-boundary bypass is supported by this patch.

`ImportantCandidate=NO` because the established primitive is a constrained UAF with shallow stale use and no demonstrated exploitation leverage beyond crash. `AutoDowngradeAllowed=YES` because there is no concrete unresolved Class A or strong Class B primitive such as repeated refcount mutation, controlled reclaim, or authorization bypass. Manual review remains recommended because it is still a real core-kernel UAF.

Likely operational severity is borderline Moderate: important to fix, but not enough evidence for an Important-class candidate.

## 5. One-sentence report phrase

A possible use-after-free in `console_flush_one_record()` can occur when legacy console handover releases the console SRCU read lock before later `con` access, leading primarily to a local kernel crash or DoS.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the patch explicitly fixes a possible UAF in core printk console handling, but the observed stale use is shallow and no controlled reclaim, arbitrary write, privilege escalation, or security-boundary bypass is established.

## 7. Call-site confidence

Call-site confidence: high

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

Patch: printk: Fix possible console use-after-free [ Upstream
Commit: f0104a7b730de32eefb3d4a27279592b5504ad59
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f0104a7b730de32eefb3d4a27279592b5504ad59

Changed files:
  kernel/printk/printk.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=f0104a7b730de32eefb3d4a27279592b5504ad59

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

The original Linux kernel CVE announcement for CVE-2026-93134 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93134

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:H/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:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 4

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).