* [CVE-2026-98283][MODERATE 7.0] KVM: PPC: Book3S HV: fix use-after-free in kvmhv_emulate_tlbie_all_lpid() [ Upstream
@ 2026-10-10 22:23 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-10-10 22:23 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98283
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: KVM: PPC: Book3S HV: fix use-after-free in kvmhv_emulate_tlbie_all_lpid() [ Upstream
Commit: 4d8f7b1f586375df8bce23a0909566ad5e852259
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4d8f7b1f586375df8bce23a0909566ad5e852259
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98283
Analysis date: Sat, 10 Oct 2026 18:23:23 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98283 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98283
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.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-98283 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98283 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=5 LEGACY=MODERATE_KPANIC RESULT=SAME (legacy and Aegis reconciliation agree; DECISION: both MODERATE_KPANIC) 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-416;CWE-362;*CWE-672;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in KVM PPC Book3S HV allows kvmhv_emulate_tlbie_all_lpid() to retain a nested guest pointer after dropping mmu_lock without holding a reference. Another vCPU can remove the same nested guest from the IDR and free it while the first vCPU still uses gp. The first vCPU can then call mutex_lock() on freed memory and access gp shadow_pgtable, gp shadow_lpid, and gp l1_host. This creates a confirmed use after free with a direct host kernel crash risk and a plausible guest to host memory corruption or privilege escalation risk. For the CVSS the PR:L reflects that an attacker must control an L1 guest with nested virtualization access and coordinate nested guest removal with TLB invalidation activity. The issue is not directly network reachable and requires execution in a guest context on an affected PowerPC Book3S HV host. AC:H applies because successful triggering depends on winning a concurrent vCPU race window. Impact is at least denial of service through a host kernel crash. In the worst defensible case the freed lock and pointer fields may enable confidentiality and integrity impact or guest to host privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE DANGER VIRT RACE UAF HARDWARE LINUS KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw conservative score: 5
* Conservative score: 5
* Raw paranoid score: 5
* Paranoid score: 5
* No floor or cap changed the score. The Real UAF floor 5 conditions are independently satisfied.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
* +2 Real UAF. The IDR-derived `gp` can be freed after `mmu_lock` is dropped and then used by the iterating vCPU.
* +1 Reliable kernel crash or strong DoS. `mutex_lock()` and subsequent field accesses operate on freed host-kernel memory and can fault or corrupt lock state.
* +1 Attacker-influenced active-object lifetime. The commit explicitly states that the free path is fully L1-controlled, and coordinated L1 vCPUs can drive removal and stale use.
* +1 Structured stale-object leverage. The stale path performs more than a shallow read: it locks freed storage and consumes `shadow_pgtable`, `shadow_lpid`, and `l1_host` during active TLB processing.
* No negative timing point. A race exists, but the L1 controls both concurrent operations and no evidence establishes a narrow, one-shot, or externally uncontrollable window.
* No hardware or niche-subsystem penalty. PowerPC Book3S HV is architecture-specific, but the supplied evidence does not establish a physical-only or sufficiently rare prerequisite under the scoring rules.
* No +2 strong exploitation leverage. Controlled reclaim, attacker-shaped replacement contents, directed host read/write, callback control, or demonstrated guest escape is not established.
* No extra Availability point. The possible host crash is already counted once.
* No Confidentiality or Integrity point. The UAF and freed-lock mutation do not independently establish disclosure or unauthorized persistent modification.
* No concrete repeated release/refcount point. The vulnerable path dereferences and locks freed `gp`, but it does not perform a second `put`, release, or refcount mutation on the same dangling reference.
* First release can end lifetime: yes, the concurrent removal path can reach `kfree(gp)`.
* Exact reference survives: yes, the iterator retains the unreferenced `gp`.
* Second lifetime/refcount mutation: no. The later vulnerable operations are `mutex_lock()` and structured field accesses.
* Concrete repeated release/refcount +1 awarded: no.
* Paranoid repeated-refcount +1 awarded: no.
* FLOOR 5 applied: no score adjustment was needed because raw scoring already reached 5.
3. Reachability analysis
The evaluated attacker is malicious L1 guest code controlling concurrent vCPUs. One vCPU can execute the all-LPID invalidation path while another issues the single-LPID operation that removes and frees the nested-guest object. The commit explicitly says the free path is fully L1-controlled, so the complete vulnerable sequence does not require host UID 0, host administrator powers, or a separate VMM lifecycle operation.
The L1 must have nested virtualization functionality available and sufficient guest-level authority to issue the relevant TLB invalidation operations. That is privilege inside the guest virtualization hierarchy, not host-administrator privilege. No Linux user-namespace or network-namespace capability participates in the trigger.
Prior host setup must provide a PowerPC Book3S HV KVM guest with nested virtualization, but the supplied sequence is guest-only after that provisioning. The trigger is not remotely network reachable. The race appears repeatable through coordinated vCPUs, so no hard-race penalty is justified.
4. Primitive and severity interpretation
The exact primitive is an active structured host-kernel UAF. `gp` is obtained from the nested-guest IDR without taking a reference. After `mmu_lock` is released, another vCPU can remove the object, drop its final reference, and free it. The first vCPU then locks freed memory and consumes multiple pointer and identity fields.
This is not fixed stale storage and is not cleanup-only behavior. It occurs during active nested-guest TLB processing. It also is not a concrete double-release case because the stale path does not perform another lifetime release on `gp`.
The demonstrated consequence is a guest-triggerable host UAF with realistic host crash or DoS and a concrete write-like operation against the freed lock field. A controlled reclaim, arbitrary host read/write, callback hijack, or guest-to-host privilege escalation remains unproven. Therefore the primitive is CLASS_B rather than CLASS_A.
ImportantCandidate is YES because the L1 controls the freeing sequence and the stale object continues into nontrivial host MMU processing involving a lock and kernel pointers. That leaves meaningful exploitation leverage unresolved even though strong guest-to-host corruption is not demonstrated. AutoDowngradeAllowed is NO because automatically treating this as ordinary crash-only Moderate would discard an active structured host UAF across a virtualization boundary.
The operational severity is Actionable Moderate at minimum, with Important classification requiring manual analysis of allocator reuse, stale lock behavior, and the subsequent uses of `shadow_pgtable` and `l1_host`.
5. One-sentence report phrase
A malicious L1 guest can race nested-guest removal against all-LPID TLB invalidation, causing the host kernel to lock and consume a freed KVM object and potentially crash the host.
6. Manual review recommendation
MANUAL CHECK REQUIRED
The confirmed active-object host UAF, L1-controlled free path, freed-lock mutation, and subsequent pointer consumption require exploitation-leverage review even though controlled reclaim or guest escape is not established.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: KVM: PPC: Book3S HV: fix use-after-free in kvmhv_emulate_tlbie_all_lpid() [ Upstream
Commit: 4d8f7b1f586375df8bce23a0909566ad5e852259
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4d8f7b1f586375df8bce23a0909566ad5e852259
Changed files:
arch/powerpc/kvm/book3s_hv_nested.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=4d8f7b1f586375df8bce23a0909566ad5e852259
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98283 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98283
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:L/I:L/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: unknown
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: YES
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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