[CVE-2026-80656][MODERATE REGULAR] hfsplus: Add a sanity check for btree node size [ Upstream

[CVE-2026-80656][MODERATE REGULAR] hfsplus: Add a sanity check for btree node size [ Upstream

[AL-KERNEL]

CVE: CVE-2026-80656
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: hfsplus: Add a sanity check for btree node size [ Upstream
Commit: 306265eb9384d2c224f1b14d83a29323f0eab6d1
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=306265eb9384d2c224f1b14d83a29323f0eab6d1
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80656
Analysis date: Fri, 28 Aug 2026 06:36:23 -0400
ActionableScore: 4
ActionableScore lower bound: 1
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
A malformed HFS Plus image with an invalid btree node_size can corrupt mount-time btree parser offset handling and trigger an uninitialized value bug in hfsplus_bnode_find, causing at least local DoS when the image is mounted and requiring manual review when automount or delegated mount paths are available.

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

The original Linux kernel CVE announcement for CVE-2026-80656 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80656

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.

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AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-80656	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	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-20;*CWE-457;CWE-1284;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'A malformed HFS Plus filesystem image can provide an invalid btree node_size such as 1 during mount. This value passes the old power of two check but is below the format minimum and can corrupt offset calculations in the btree parser, leading to use of an uninitialized value in hfsplus_bnode_find. For the CVSS the PR:L value is used in the paranoid view because some deployments may allow a local user to reach this path through delegated mount capability, container root, loop device access, or an automount workflow. The issue is not network reachable and requires local interaction with filesystem mounting rather than packet processing. Impact is primarily denial of service through a kernel warning crash or failed mount path. No concrete information leak or write primitive is evident from the code context, so confidentiality and integrity are not increased above N in this assessment.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 3)  SKIP CVE-2026-80656 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	READ KASAN DISK LINUS SYZBOT  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=4
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 4
* Final recommended bucket: **Borderline, manual review recommended**::

## 2. Signal breakdown

Conservative signals:

* Reliable kernel crash / strong DoS: +1. Syzbot reports KMSAN uninit-value during HFS Plus mount from a corrupted image.
* Validation/state-corruption concern: +1. The patch adds missing validation for btree node_size before parser use.
* Important filesystem/storage parser path: +1. The bug is in filesystem mount-time metadata parsing.
* Requires admin/root/CAP_SYS_ADMIN in typical deployments: -2. Mounting arbitrary block filesystem images normally requires privileged mount capability.

Conservative total: 1

Paranoid signals:

* Local unprivileged trigger: +1. Some deployments may expose this path through automount, desktop removable media handling, container root, delegated mount helpers, or loop-device workflows.
* Reliable kernel crash / strong DoS: +1. Malformed filesystem metadata can reach the mount path and trigger a sanitizer-detected uninitialized value bug.
* Validation/state-corruption concern: +1. Invalid node_size can corrupt parser offset calculations before the new lower-bound check rejects it.
* Important filesystem/storage parser path: +1. Filesystem image parsers historically deserve manual review even when the first visible symptom is a sanitizer report.

Paranoid total: 4

## 3. Reachability analysis

The realistic trigger is a malformed HFS Plus filesystem image mounted by the kernel. In normal server deployments this usually requires CAP_SYS_ADMIN or a privileged mount helper, so conservative reachability is local privileged. In desktop, removable-media, automount, container, or delegated mount environments, a local low-privileged user may be able to get a crafted image processed indirectly, which supports the paranoid PR:L interpretation. The issue is not network reachable by itself.

Call-site confidence: high. The supplied trace shows the path through hfsplus_fill_super, hfsplus_btree_open, and hfsplus_bnode_find during mount.

## 4. Severity interpretation

This behaves more like a borderline actionable Moderate than an Important-class issue. The patch supports malformed-input parser failure and uninitialized value use, with plausible local DoS. It does not show UAF, OOB write, arbitrary write, refcount misuse, callback control, page-cache corruption, or a clear privilege-escalation primitive. The paranoid score is raised for filesystem parser exposure and possible unprivileged mount mediation, not for proven memory corruption beyond the uninitialized-value report.

## 5. One-sentence report phrase

A malformed HFS Plus image with an invalid btree node_size can corrupt mount-time btree parser offset handling and trigger an uninitialized value bug in hfsplus_bnode_find, causing at least local DoS when the image is mounted and requiring manual review when automount or delegated mount paths are available.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED. YES REQUIRES MANUAL CHECK.

Reason: malformed filesystem parser input plus sanitizer finding is enough for manual review, but current evidence supports DoS only and does not justify Important-class scoring without an additional corruption or privilege-escalation primitive.

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

Patch: hfsplus: Add a sanity check for btree node size [ Upstream
Commit: 306265eb9384d2c224f1b14d83a29323f0eab6d1
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=306265eb9384d2c224f1b14d83a29323f0eab6d1

Changed files:
  fs/hfsplus/bnode.c
  fs/hfsplus/btree.c
  fs/hfsplus/super.c
  fs/super.c
  fs/namespace.c
  include/linux/hfs_common.h

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=306265eb9384d2c224f1b14d83a29323f0eab6d1

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

The original Linux kernel CVE announcement for CVE-2026-80656 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80656

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:L/PR:H/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: 1
  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).