* [CVE-2026-99168][LOW] mshv_vtl: Check per-CPU register page before mmap
@ 2026-10-30 16:20 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-10-30 16:20 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-99168
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: mshv_vtl: Check per-CPU register page before mmap
Commit: 5c0757b065fbd140d8fbd05dc2c2146b713dfa68
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5c0757b065fbd140d8fbd05dc2c2146b713dfa68
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99168
Analysis date: Fri, 30 Oct 2026 12:20:23 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
A local `mshv_vtl` mapping fault can pass a missing per-CPU register page to `get_page()`, causing a host-kernel NULL-pointer crash.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99168 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99168
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-2026-99168 LOW https://www.kernelcve.org/list/?q=CVE-2026-99168 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 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:L/UI:N/S:U/C:N/I:N/A:H';**CWE-476;CWE-703;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'The mshv_vtl mmap fault path trusts a global register page flag even though register page setup can succeed for one CPU and fail for another. A local process can fault a mapping for a CPU whose selected page is NULL and reach get_page with a NULL pointer which can crash the host kernel. For the CVSS the PR:L value is used because triggering requires local access to the mshv_vtl device and its mmap interface but this access may be delegated to a VTL management process or service account rather than requiring unrestricted host administration. AC:H is used for the base score because mixed per-CPU setup results must already exist. The demonstrated primitive is a NULL pointer dereference with availability impact only and there is no supported UAF OOB write information leak or privilege escalation primitive. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 5.5 and the production ActionableScore returned 2 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were final reconciliation stage LOW to LOW because KP specialist did not establish a qualifying panic and 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 KPANIC_UNSUPPORTED_REMOVED and V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED. The independent weaker Aegis shadow evaluated CVSS 2.5 and ActionableScore 1 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.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) MAYBE READ INIT WARNONLY SIMPLEFIX LEAK HARDWARE LINUS KPANIC_UNSUPPORTED_REMOVED V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 2.
* Conservative score: 2; no floor or cap applied.
* Raw paranoid score: 2.
* Paranoid score: 2; no stronger patch-supported primitive exists.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +1 weak/indirect invalid-pointer behavior: mixed per-CPU setup can select a NULL `reg_page`, which is passed to `get_page()`.
* +1 reliable kernel crash/strong DoS: `get_page(NULL)` plausibly faults in the host kernel.
* No timing penalty: mixed setup results are a state precondition, not a demonstrated narrow race.
* No privilege penalty: device permissions and the complete setup/trigger authority are unresolved, so host-admin privilege cannot be assumed.
* No UAF, OOB write, controlled overwrite, disclosure, authorization bypass, or integrity primitive is shown.
* No additional availability point: it would duplicate the same NULL-dereference crash.
* B5-R and B3-PENDING do not apply; there is no retry-accumulated OOB write or shared-backing write.
3. Reachability analysis
A local process with access to the `mshv_vtl` mmap interface can fault the CPU-specific mapping after register-page setup succeeds for one CPU but fails for another. The evidence does not establish ordinary-user device access, mandatory host administration, namespace-scoped capability checks, or attacker control over the allocation/registration failure. No special race is required once the mixed state exists, but creation of that state may depend on environmental failure.
4. Primitive and severity reading
The exact primitive is a NULL page pointer passed to `get_page()`. This is neither stale storage nor an active structured-object UAF, and no repeated release/refcount operation exists. The demonstrated consequence is crash/DoS-class invalid-pointer behavior, so `CLASS_C` is appropriate. Memory corruption or useful effects after excluding the crash are unsupported. Consequently, this is not an Important candidate and can be downgraded based on current evidence, though deployment-specific device access warrants review.
5. One-sentence report phrase
A local `mshv_vtl` mapping fault can pass a missing per-CPU register page to `get_page()`, causing a host-kernel NULL-pointer crash.
6. Manual review advice
MANUAL CHECK RECOMMENDED
Confirm device-node permissions and whether an attacker can induce or reliably encounter mixed per-CPU register-page setup.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: mshv_vtl: Check per-CPU register page before mmap
Commit: 5c0757b065fbd140d8fbd05dc2c2146b713dfa68
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5c0757b065fbd140d8fbd05dc2c2146b713dfa68
Commit description:
Register-page setup is optional for each CPU. If allocation or
registration fails, mshv_vtl_configure_reg_page() warns and leaves that
CPU's reg_page NULL, but initial context setup continues successfully.
Meanwhile, successful setup on another CPU sets the global
mshv_has_reg_page flag.
mshv_vtl_fault() checks this global flag before selecting the requested
CPU's register page. With mixed setup results across online CPUs, the
check passes even for a CPU with no register page, reaching
get_page(NULL) when userspace faults in that mapping.
Check the selected per-CPU register page before taking its reference and
return VM_FAULT_SIGBUS if it is absent.
Fixes: 7bfe3b8 ("Drivers: hv: Introduce mshv_vtl driver")
Cc: [email protected]
Signed-off-by: Hardik Garg <[email protected]>
Reviewed-by: Naman Jain <[email protected]>
Signed-off-by: Wei Liu <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
drivers/hv/mshv_vtl_main.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=5c0757b065fbd140d8fbd05dc2c2146b713dfa68
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99168 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99168
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:L/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 5.5
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: 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: 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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