[CVE-2026-80896][MODERATE 7.0] mshv: Fix race in mshv_irqfd_deassign [ Upstream

[CVE-2026-80896][MODERATE 7.0] mshv: Fix race in mshv_irqfd_deassign [ Upstream

[AL-KERNEL]

CVE: CVE-2026-80896
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: mshv: Fix race in mshv_irqfd_deassign [ Upstream
Commit: 72a90ce4918b5a2d4820fe20677ba9af780d8826
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=72a90ce4918b5a2d4820fe20677ba9af780d8826
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80896
Analysis date: Fri, 04 Sep 2026 16:02:25 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline manual review recommended / Actionable Moderate watchlist
Manual review required: YES

Summary:
A race in `mshv_irqfd_deassign()` can allow concurrent irqfd deactivation and a double `hlist_del()` on poisoned list pointers, causing a local host kernel crash, with PR:L in delegated VMM access scenarios and no direct network reachability.

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

The original Linux kernel CVE announcement for CVE-2026-80896 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80896

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
======================================================================

CVE-2026-80896	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-80896 CHECK WITH IMPACT FROM ORIG NN LOW	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-362;CWE-667;*CWE-672;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'mshv_irqfd_deassign() misses pt_irqfds_lock while traversing pt_irqfds_list, racing with the EPOLLHUP path that can deactivate the same irqfd under the lock. Because hlist_del() poisons node pointers and mshv_irqfd_is_active() only checks hlist_unhashed(), a second deactivate path can still treat the node as active and call hlist_del() again on poisoned pointers. This can crash the host kernel and may create list state corruption around irqfd cleanup work. For the CVSS the PR:L value is used because triggering requires local access to /dev/mshv or a VMM process context, not remote network access. The issue is not network reachable. Impact is at least local denial of service. In the paranoid view, limited confidentiality or integrity impact cannot be fully excluded because this is a race around shared kernel list state, but no arbitrary write primitive is proven.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / Actionable Moderate watchlist (with actual score 4)	YES	LOCK INIT SIMPLEFIX RACE IMPROVEONLY  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK	YES	NO	checked

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

ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline manual review recommended / Actionable Moderate watchlist**::

## 2. Signal breakdown

* Local unprivileged or low privileged trigger: +1
  Triggering appears to require local access to `/dev/mshv` or a VMM process context, not full host root in all deployments.

* Memory corruption, weak or indirect corruption candidate: +1
  The bug can cause a double `hlist_del()` on poisoned hlist pointers. This is kernel list metadata corruption, but no controlled overwrite, reclaim, type confusion, or arbitrary write primitive is shown.

* Real lifetime or list state corruption: +1
  `hlist_del()` leaves poisoned pointers while `mshv_irqfd_is_active()` relies on `hlist_unhashed()`. This creates an incorrect active state after removal and allows a second deactivate path.

* Reliable kernel crash / strong DoS: +1
  A double deletion of poisoned hlist pointers is a realistic host kernel crash condition.

* Hard or unreliable race / special timing required: -1
  The issue depends on a race between `mshv_irqfd_deassign()` and the EPOLLHUP path in `mshv_irqfd_wakeup()`.

* Paranoid extra concern: +1
  The paranoid score keeps a small integrity concern because the race affects shared kernel list state and asynchronous cleanup work. This does not imply strong LPE plausibility.

## 3. Reachability analysis

The bug is locally reachable through mshv irqfd management, likely by a VMM process or another local actor that can access `/dev/mshv` and manipulate irqfd or eventfd state. It is not network reachable. For the CVSS the PR:L value is reasonable in environments where `/dev/mshv` access is delegated to a non-root VMM or service account, because that actor is not equivalent to full host root.

Namespaces and containers may matter if `/dev/mshv` is exposed into a container or delegated to a reduced-capability virtualization service. In a stricter deployment where only full host root can access mshv, the practical severity is lower. The subsystem is not a broad default Linux attack surface and depends on Hyper-V mshv usage.

Call-site confidence: high for the race and double-delete mechanism because both affected functions and the competing path are described. Medium for exploitability beyond DoS because no reclaim, controlled overwrite, callback control, or privilege escalation primitive is shown.

## 4. Severity interpretation

This behaves primarily like a local race-triggered kernel DoS with weak list-state corruption. It is not an ordinary Low issue because the patch fixes missing locking plus incorrect hlist deletion semantics that can produce double deletion on poisoned pointers. It is also not a strong Important candidate based on the supplied evidence, because there is no demonstrated attacker-controlled memory reuse, arbitrary write, type confusion, or privilege escalation path.

The realistic impact is host kernel crash. The theoretical memory corruption concern is limited to kernel list metadata corruption around irqfd cleanup and should be manually reviewed, but it should not be upgraded to strong LPE without additional evidence.

## 5. One-sentence report phrase

A race in `mshv_irqfd_deassign()` can allow concurrent irqfd deactivation and a double `hlist_del()` on poisoned list pointers, causing a local host kernel crash, with PR:L in delegated VMM access scenarios and no direct network reachability.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED. YES REQUIRES MANUAL CHECK.

Reason: this is a race in kernel list/lifetime handling with a double-delete condition on poisoned hlist pointers. The current evidence supports DoS and weak corruption concern, but not confirmed privilege escalation.

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

Patch: mshv: Fix race in mshv_irqfd_deassign [ Upstream
Commit: 72a90ce4918b5a2d4820fe20677ba9af780d8826
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=72a90ce4918b5a2d4820fe20677ba9af780d8826

Changed files:
  drivers/hv/mshv_eventfd.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=72a90ce4918b5a2d4820fe20677ba9af780d8826

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

The original Linux kernel CVE announcement for CVE-2026-80896 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80896

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: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: 3
  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: 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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).