[CVE-2026-80536][MODERATE 7.0] xfs: bounds-check buffer log item's dirty bitmap

[CVE-2026-80536][MODERATE 7.0] xfs: bounds-check buffer log item's dirty bitmap

[AL-KERNEL]

CVE: CVE-2026-80536
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: xfs: bounds-check buffer log item's dirty bitmap
Commit: f8288214459ead7e87d26e5822f62c14a4f2ed6b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f8288214459ead7e87d26e5822f62c14a4f2ed6b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80536
Analysis date: Wed, 26 Aug 2026 13:04:10 -0400
ActionableScore: 8
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A crafted XFS image can trigger an attacker-influenced slab out-of-bounds write during mount-time log recovery because dirty bitmap offsets were not runtime-checked against the recovered buffer length, making this at least a strong DoS and a plausible LPE candidate in delegated mount workflows.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-80536 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80536

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
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CVE-2026-80536	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-122;*CWE-20;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H';BEST CVSS score: '7.8';DESCR 'A slab out of bounds write can occur in the XFS mount time log recovery path because xlog_recover_do_reg_buffer used a dirty bitmap from the on disk buffer log item without a real runtime bounds check against the allocated buffer length. A crafted XFS image can encode a small blf_len together with dirty bitmap bits that point past the end of that buffer, causing memcpy to corrupt adjacent kernel heap memory during recovery. For the CVSS the PR:L is used for the paranoid score because a reduced capability local user, container root, storage management service account, or delegated mount workflow may be able to cause a crafted XFS image to be mounted without full host administrator control. The issue is not network reachable by itself and requires the malicious filesystem image to be mounted locally. Impact can include kernel crash and, because the primitive is an attacker influenced kernel heap out of bounds write, potential privilege escalation or broader confidentiality and integrity impact should be considered.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) 	MAYBE	WRITE KASAN OOB DISK LOG IMPROVEONLY LINUS KPANIC  DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=8
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 8
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**

## 2. Signal breakdown

### Conservative score: 5

Triggered signals:

* Memory corruption, Strong corruption primitive: +2
  The patch and commit explicitly describe a production-kernel slab out-of-bounds write from memcpy during XFS log recovery.

* Weak LPE concern: +1
  The write is attacker-influenced through crafted on-disk log metadata and data, but the exact adjacent heap target and exploitation reliability are not demonstrated.

* Memory layout invariant restoration: +1
  The fix restores a missing runtime invariant between the dirty bitmap offset/length and the allocated buffer length derived from blf_len.

* Reliable kernel crash / strong DoS: +1
  KASAN confirmed slab-out-of-bounds write before the fix. A crafted image can plausibly crash the kernel during mount-time recovery.

* Important filesystem/storage path: +1
  This is XFS journal/log recovery code, a critical filesystem metadata path.

* Confidentiality impact plausible: +1
  Not a direct info leak, but plausible as a secondary consequence of kernel heap corruption.

* Integrity impact plausible: +1
  The primitive is a write past an allocated kernel heap buffer.

* Requires admin/root/CAP_SYS_ADMIN in typical deployments: -2
  Mounting a crafted XFS image normally requires administrative mount privileges.

* Corruption target not fully demonstrated / heap adjacency uncertainty: -1
  The overflow is real, but the patch does not show controlled target selection or a complete exploit primitive.

Conservative total: 5

### Paranoid score: 8

Paranoid changes:

* Privilege escalation plausible, stronger interpretation: +2 instead of +1
  The primitive is an attacker-influenced kernel heap out-of-bounds write, which is a class historically capable of LPE when heap placement and payload control are sufficient.

* Local low-privilege or delegated trigger concern: +1
  While normal mounting is privileged, real deployments may involve automount, image ingestion, storage management services, container root, reduced-capability root, or delegated mount workflows.

* Privilege penalty reduced: -1 instead of -2
  The attacker may not have full host-root equivalence in practical workflows that mount user-supplied images.

Paranoid total: 8

## 3. Reachability analysis

The bug is reachable during XFS mount-time log recovery when a crafted filesystem image contains inconsistent buffer log item metadata. The attacker must cause the crafted image to be mounted. In a default local system this usually requires CAP_SYS_ADMIN or root, so the conservative interpretation is privileged local reachability.

Namespaces and containers may affect the practical privilege requirement. Container root, a storage service account, image-scanning service, backup system, removable-media automount path, or other delegated mount workflow can reduce the practical barrier compared with full host administrator control. The issue is not network reachable by itself, but it can become reachable through systems that automatically or semi-automatically mount untrusted storage images.

Call-site confidence: high. The patch shows the changed helper and all visible callers propagating the new error path.

## 4. Severity interpretation

This is not an ordinary Moderate cleanup. The patch fixes a concrete slab out-of-bounds write in kernel heap memory, confirmed by KASAN on a non-debug production-style build. Conservative handling is Actionable Moderate because typical triggering requires mount privileges. Paranoid handling is a Strong Important candidate because the primitive is attacker-influenced kernel heap corruption in a critical filesystem recovery path and practical deployments may expose mounting of crafted images through reduced-privilege workflows.

The realistic demonstrated impact is kernel crash or filesystem recovery failure. The theoretical higher impact is privilege escalation or broader confidentiality/integrity compromise through heap corruption, but no complete exploit chain is demonstrated in the patch.

## 5. One-sentence report phrase

A crafted XFS image can trigger an attacker-influenced slab out-of-bounds write during mount-time log recovery because dirty bitmap offsets were not runtime-checked against the recovered buffer length, making this at least a strong DoS and a plausible LPE candidate in delegated mount workflows.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: confirmed kernel heap out-of-bounds write in a critical filesystem recovery path, with attacker-controlled on-disk metadata and plausible reduced-privilege exposure through image mounting workflows.

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

Patch: xfs: bounds-check buffer log item's dirty bitmap
Commit: f8288214459ead7e87d26e5822f62c14a4f2ed6b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f8288214459ead7e87d26e5822f62c14a4f2ed6b

Commit description:

xlog_recover_do_reg_buffer() replays each dirty region described by a
buffer log item's bitmap into the buffer read for that item:

	memcpy(xfs_buf_offset(bp, (uint)bit << XFS_BLF_SHIFT),
		item->ri_buf[i].iov_base,
		nbits << XFS_BLF_SHIFT);

The destination offset (bit/nbits, from the logged dirty bitmap) and the
buffer size (from the logged blf_len) are both attacker-controlled and
otherwise unrelated, yet the only thing bounding the copy is an ASSERT(),
which compiles away on production kernels. A crafted image logging a
small blf_len together with a bitmap bit past the end of that buffer
drives the memcpy() past the buffer's allocation, corrupting adjacent
kernel heap during mount-time log recovery. This is reachable by anyone
who can get a crafted image mounted -- the malicious-filesystem threat
model XFS already guards against elsewhere.

Turn the ASSERT() into a real XFS_IS_CORRUPT() check that aborts recovery
of the buffer with -EFSCORRUPTED, consistent with the validate-and-fail
idiom already used in xlog_recover_do_inode_buffer() and
xfs_dquot_item_recover.c. xlog_recover_do_reg_buffer() therefore becomes
STATIC int and its three callers propagate the error.

Found and confirmed with KASAN on a CONFIG_XFS_DEBUG=n build: the crafted
image trips a slab-out-of-bounds write before this change and fails
recovery cleanly with -EFSCORRUPTED after it.

Fixes: 1da177e ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Ibrahim Hashimov <security@auditcode.ai>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/xfs/xfs_buf_item_recover.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=f8288214459ead7e87d26e5822f62c14a4f2ed6b

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

The original Linux kernel CVE announcement for CVE-2026-80536 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80536

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:H/I:H/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

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: 5
  Paranoid ActionableScore: 8

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).