[CVE-2026-90161][MODERATE 7.0] erofs: fix interlaced ztailpacking pclusters [ Upstream

[CVE-2026-90161][MODERATE 7.0] erofs: fix interlaced ztailpacking pclusters [ Upstream

[AL-KERNEL]

CVE: CVE-2026-90161
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: erofs: fix interlaced ztailpacking pclusters [ Upstream
Commit: ddb7ea4fd99bf6c4314d1dfca18aec6945ce8054
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ddb7ea4fd99bf6c4314d1dfca18aec6945ce8054
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90161
Analysis date: Thu, 17 Sep 2026 12:52:14 -0400
ActionableScore: 5
ActionableScore lower bound: 4
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-2026-90161 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90161

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-2026-90161	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-90161 CHECK WITH IMPACT FROM ORIG NN MODERATE	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:N/A:N';CWE-125;*CWE-200;*CWE-20;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:N';BEST CVSS score: '5.5';DESCR 'An out-of-bounds read in the EROFS decompression path can occur when a crafted image contains invalid interlaced ztailpacking pclusters. The kernel may read beyond the expected mapped page data and copy unrelated kernel memory into userspace-visible page cache when the affected file data is read. For the CVSS the PR:L is used in the paranoid score because a local user or service account may be able to provide or mount crafted EROFS images in container, appliance, or automount workflows, even though direct mounting is often administrative. The issue is local and is not network reachable by itself. Impact is information disclosure of kernel memory with no direct evidence of integrity impact or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	YES	READ OOB DANGER DISK SIMPLEFIX LINUS KPANIC 	YES	NO	guess

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

ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 4
* Conservative score: 4. No floor or cap applied.
* Raw paranoid score: 4
* Paranoid score: 5. Applied paranoid floor 4 -> 5 because the patch establishes a concrete kernel memory disclosure path into userspace-visible page cache from a crafted filesystem image.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Positive signals:

* +2: Concrete user-visible kernel memory disclosure primitive. The commit explicitly states that crafted EROFS images can cause an out-of-bounds read from a kmap'd page and copy irrelevant kernel memory into userspace-visible page cache.
* +1: Confidentiality impact is plausible and directly supported. The disclosed bytes are copied into page cache visible to userspace when affected file data is read.
* +1: Important filesystem and page-cache path. The bug is in EROFS decompression and mapping logic, affecting how crafted on-disk data is interpreted and exposed through normal file reads.

Negative or non-awarded signals:

* +0: No RealUAF. The supplied patch establishes OOB read and disclosure, not use-after-free.
* +0: No integrity impact awarded. The patch does not show unauthorized writes, COW violation, metadata modification, or page-cache corruption.
* +0: No availability point awarded. The demonstrated consequence is disclosure, not kernel crash or persistent DoS.
* +0: No remote reachability awarded. The issue requires a crafted filesystem image to be mounted or otherwise processed locally.
* +0: No local unprivileged trigger awarded. Below-host-admin reachability is plausible in appliance, container, automount, or image-processing workflows, but the complete trigger chain is not established by the supplied evidence.
* +0: No arbitrary read primitive awarded. The leak is an OOB read into userspace-visible page cache, but the supplied evidence does not establish attacker-controlled address selection.
* +0: No LPE or strong corruption leverage awarded. There is no UAF, arbitrary write, controlled reclaim, or credential/security-state corruption.

3. Reachability analysis

The direct trigger requires a crafted EROFS image containing invalid interlaced ztailpacking pclusters. A normal mkfs.erofs image is not expected to generate this state, so ordinary valid filesystems are not affected.

Direct mounting of a crafted filesystem image usually requires administrative mount privileges such as CAP_SYS_ADMIN. However, the complete attacker model is not fully resolved because crafted filesystem images may be supplied to automount, container, appliance, removable-media, or image-processing workflows where the attacker controls the image but not necessarily the privileged mount operation.

Therefore HostAdminRequired is UNKNOWN rather than YES. Host-admin-equivalent privilege is common for direct mounting, but the supplied evidence does not prove that every realistic trigger requires the attacker to hold host admin privileges.

NamespaceScopedPrivilege is UNKNOWN. The input does not establish that EROFS mounting and the complete vulnerable read path are fully available through attacker-created namespaces.

No network trigger is established. The issue is local by itself and depends on local processing of a crafted filesystem image.

No race or special timing requirement is involved. The bug is a deterministic malformed-image parsing and decompression-state issue.

4. Primitive and severity interpretation

The exact primitive is an out-of-bounds read from a kmap'd page during EROFS decompression of crafted interlaced ztailpacking pclusters. The read data can be copied into userspace-visible page cache, creating a concrete kernel memory information disclosure path.

This is not active structured UAF and not fixed stale storage. It is malformed filesystem metadata causing invalid decompression or mapping semantics.

PrimitiveClass is CLASS_A because a meaningful kernel memory disclosure primitive is directly established. It is not CLASS_B because no lifetime violation is present, and not CLASS_C because the demonstrated behavior is not merely crash or invalid-state behavior.

The demonstrated consequence is kernel memory disclosure. The speculative consequence could include leakage of sensitive kernel data depending on what memory is adjacent or exposed through the page cache, but no arbitrary read, integrity impact, or privilege escalation is established.

ImportantCandidate is YES because the issue exposes kernel memory to userspace-visible file cache and requires manual evaluation of practical mount and image-ingestion paths.

AutoDowngradeAllowed is NO because automatically closing a concrete kernel memory disclosure from a crafted filesystem image would risk losing an actionable security issue, even though direct exploitation may require a privileged or delegated mount workflow.

Likely operational severity is Actionable Moderate, with Strong Important review justified if the affected product processes untrusted EROFS images below host-admin privilege.

5. One-sentence report phrase

A crafted EROFS image with invalid interlaced ztailpacking pclusters can cause an out-of-bounds read in the decompression path and copy unrelated kernel memory into userspace-visible page cache, resulting in local kernel information disclosure.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch explicitly establishes user-visible kernel memory disclosure, and practical severity depends on whether untrusted users can supply EROFS images to a mount, automount, container, appliance, or image-processing workflow.

7. Call-site confidence

Call-site confidence: high

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

Patch: erofs: fix interlaced ztailpacking pclusters [ Upstream
Commit: ddb7ea4fd99bf6c4314d1dfca18aec6945ce8054
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ddb7ea4fd99bf6c4314d1dfca18aec6945ce8054

Changed files:
  fs/erofs/decompressor.c
  fs/erofs/zmap.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=ddb7ea4fd99bf6c4314d1dfca18aec6945ce8054

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

The original Linux kernel CVE announcement for CVE-2026-90161 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90161

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:N/A:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
  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: 4
  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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).