* [CVE-2026-99093][LOW] mm: don't schedule deferred kernel page table freeing while booting
@ 2026-10-27 2:03 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-10-27 2:03 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-99093
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: mm: don't schedule deferred kernel page table freeing while booting
Commit: 7a25ca170c12a9328f6fcf4410713beb516b01c0
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7a25ca170c12a9328f6fcf4410713beb516b01c0
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99093
Analysis date: Mon, 26 Oct 2026 22:03:24 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
A host administrator can configure boot-time function tracing to reach premature workqueue scheduling and deterministically panic the kernel during boot.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99093 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99093
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-2026-99093 LOW https://www.kernelcve.org/list/?q=CVE-2026-99093 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=0 LEGACY=LOW RESULT=DIFF TEMP_DISTANCE_MERGE_SKIP=AEGIS_NO_POSITIVE_SEVERITY_EVIDENCE (final Legacy and Aegis differ; FINAL: LOW, Aegis: MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';**CWE-476;CWE-665;CWE-908;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.4';DESCR 'An initialization ordering bug allows pagetable_free_kernel to schedule deferred page table freeing before the required workqueue exists. A boot time function tracer and a suitable filter can reach this path while system_percpu_wq is still NULL, causing a NULL pointer dereference in __queue_work and a kernel panic during boot. For the CVSS the PR:H value is selected because reliable triggering normally requires administrative control of the kernel command line and a system reboot. The issue is not network reachable and the demonstrated primitive is a deterministic boot failure with availability impact only, lacking evidence of UAF, OOB access, information disclosure, or privilege escalation. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 4.4 and the production ActionableScore returned 0 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE_KPANIC to MODERATE because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE to LOW because the ActionableScore threshold rule was applied. final reconciliation stage LOW to LOW because the cross model evidence reconciliation rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS and DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 and V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED. The independent weaker Aegis shadow evaluated CVSS 4.3 and ActionableScore 0 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0) MAYBE KASAN OOB NULLPTR INIT HARDWARE BOOT MEMORY DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=0
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: -1.
* Conservative score: 0 after normalizing the negative raw score to the score range.
* Raw paranoid score: -1.
* Paranoid score: 0 after normalization; no technically supported additional effect.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +1 Reliable kernel crash: the demonstrated boot-time tracing path calls `schedule_work()` before `system_percpu_wq` exists, causing a NULL-pointer fault and panic.
* -2 Proven host-administrator-equivalent prerequisite: the demonstrated trigger requires boot-time function-tracer/filter configuration and reboot control.
* No OOB write, UAF, stale-object use, attacker-controlled corruption, authorization bypass, disclosure, or integrity effect is shown.
* No extra availability point: the boot panic is the same effect already counted.
* NEW52/B5-R does not apply: there is no heap OOB write or retry-accumulated index.
* B3-PENDING and B4-PENDING do not apply: no shared-backing write or DENY-to-ALLOW authorization change exists.
3. Reachability analysis
The evidenced trigger is early boot with a specially configured function tracer and filter. Controlling the kernel command line and reboot is effectively host-administrative, although numeric host UID 0 specifically is not established. No normal-user, namespace-capability, delegated-interface, network, or post-boot trigger is shown. There is no race: the failure follows deterministic initialization ordering. No unusual hardware is required.
4. Primitive and severity reading
The primitive is an initialization-order NULL-pointer dereference: kernel page-table freeing queues valid deferred work before the underlying workqueue exists. The page table is first placed on a list; the fault occurs while scheduling work, not through a UAF or page-table corruption. The fix defers scheduling until after workqueue initialization and drains early entries through a core initcall.
This is CLASS_C crash/boot-availability behavior. No useful primitive remains after excluding the panic, so it is not an Important candidate and automatic downgrade is allowed. Likely operational severity is Low-like to ordinary Moderate because exploitation requires control equivalent to configuring and rebooting the host.
5. One-sentence report phrase
A host administrator can configure boot-time function tracing to reach premature workqueue scheduling and deterministically panic the kernel during boot.
6. Manual review advice
NO MANUAL CHECK NEEDED
The patch and trace establish a privileged, availability-only initialization failure without a corruption or security-boundary primitive.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: mm: don't schedule deferred kernel page table freeing while booting
Commit: 7a25ca170c12a9328f6fcf4410713beb516b01c0
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7a25ca170c12a9328f6fcf4410713beb516b01c0
Commit description:
Booting with a boot-time function tracer and a filter, for example
ftrace=function ftrace_filter=pud_free_pmd_page
panics on 7.3-rc4 as soon as the tracer starts:
[ 23.531178] Starting tracer 'function'
[ 23.675800] Oops: general protection fault, probably for non-canonical address 0xdffffc0000000038: 0000 [#1] SMP KASAN NOPTI
[ 23.819917] KASAN: null-ptr-deref in range [0x00000000000001c0-0x00000000000001c7]
[ 23.964025] CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 7.3.0-rc4-fe2ec83746e5-with-fixes-v2+ #195 PREEMPT(undef)
[ 24.252248] RIP: 0010:__queue_work+0xab/0xf00
[ 25.981629] Call Trace:
[ 26.125727] <TASK>
[ 26.413912] ? pagetable_free_kernel+0x20/0x120
[ 26.990283] queue_work_on+0x97/0xf0
[ 27.134382] __cpa_collapse_large_pages+0x501/0x6f0
[ 27.566662] cpa_flush+0x394/0x620
[ 27.998953] change_page_attr_set_clr+0x321/0x4a0
[ 29.151729] set_memory_rox+0xa2/0xf0
[ 29.584018] create_trampoline+0x431/0x6f0
...
[ 44.343347] Kernel panic - not syncing: Attempted to kill the idle task!
The boot-time tracer is started from early_trace_init(), which runs
before workqueue_init_early(). Making its trampoline read-only splits a
large page, and CPA collapses it again right away. The split table has
been a kernel page table since commit 9e4a3ec
("x86/mm/pat: Allocate split page tables as kernel page tables"), so the
collapse frees it through pagetable_free_kernel(), which queues work on
system_percpu_wq - still NULL at that point. That commit is correct in
itself; it only lets CPA reach pagetable_free_kernel() before the
workqueue that function relies on exists.
Keep putting the table on the list, but don't schedule the work while
the system is still booting. A core_initcall schedules it once to free
whatever was queued by then.
Link: https://lore.kernel.org/[email protected]
Link: https://lore.kernel.org/[email protected]
Fixes: 9e4a3ec ("x86/mm/pat: Allocate split page tables as kernel page tables")
Signed-off-by: Mikhail Gavrilov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Suggested-by: David Hildenbrand (Arm) <[email protected]>
Suggested-by: Lorenzo Stoakes (ARM) <[email protected]>
Reviewed-by: Andrew Morton <[email protected]>
Reviewed-by: David Hildenbrand (Arm) <[email protected]>
Reviewed-by: Lorenzo Stoakes (ARM) <[email protected]>
Reviewed-by: Jose A. Perez de Azpillaga <[email protected]>
Tested-by: Jose A. Perez de Azpillaga <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Liam R. Howlett <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Vishal Moola (Oracle) <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Lu Baolu <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
mm/pgtable-generic.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=7a25ca170c12a9328f6fcf4410713beb516b01c0
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99093 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99093
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:L/PR:H/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 4.4
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: unknown
Paranoid ActionableScore: 0
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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