* [CVE-2026-98067][LOW] erofs: disable LZ4 rolling decompression for now [ Upstream
@ 2026-09-25 18:07 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-25 18:07 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98067
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: erofs: disable LZ4 rolling decompression for now [ Upstream
Commit: ec52dfed7b14514ed97ee71161e4cf4cfe2fbff2
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ec52dfed7b14514ed97ee71161e4cf4cfe2fbff2
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98067
Analysis date: Fri, 25 Sep 2026 14:07:55 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98067 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98067
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: LOW
Manual review required: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-98067 LOW https://www.kernelcve.org/list/?q=CVE-2026-98067 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:L/A:L';CWE-682;CWE-665;*CWE-20;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:L/A:N';BEST CVSS score: '3';DESCR 'An EROFS LZ4 rolling decompression correctness issue occurs because the rolling window optimization assumes that literal data is copied forward. The upstream LZ4 implementation can copy long literals backward even for non overlapping source and destination ranges, which can invalidate reuse assumptions for temporary pages and produce incorrect decompressed file data. For the CVSS the PR:H reflects that reliably triggering the issue normally requires administrative capability to mount or control a crafted EROFS filesystem image. The issue is not directly network reachable. Impact is primarily integrity impact on data read from the affected filesystem. The patch context does not demonstrate an out of bounds access, use after free, arbitrary write, information disclosure, or plausible privilege escalation primitive.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0) YES OOB DANGER DISK INIT LINUS MEMORY DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 YES NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=0
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 0
* Conservative score: 0
* Raw paranoid score: 0
* Paranoid score: 0
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* No positive primitive score. The patch establishes a decompression correctness defect, not a memory-safety, ownership, authorization, or lifetime primitive.
* No UAF, double free, stale reference, out of bounds access, arbitrary write, controlled reclaim, or refcount mutation is demonstrated.
* No confidentiality score. The patch does not establish exposure of data from another security domain.
* No integrity score. Incorrect decompression may affect bytes read from the affected EROFS image, but there is no demonstrated unauthorized modification of protected kernel state, another principals data, shared storage, or an independently permissioned file.
* No availability score. The supplied evidence does not establish a kernel crash, filesystem shutdown, persistent resource exhaustion, or host-wide denial of service.
* No remote reachability score. The vulnerable operation is local filesystem decompression.
* No filesystem ownership or COW score. The issue is not a demonstrated shared-page or cross-file ownership violation.
* No broad exposure score. EROFS may be broadly deployed, but the vulnerable rolling LZ4 path and a suitable compressed extent are required. Broad deployment alone is not an actionable security primitive.
* Negative reachability condition: mounting and controlling a crafted EROFS filesystem image normally requires host-admin-equivalent mount capability. EROFS is not a general unprivileged user-namespace mount filesystem.
3. Reachability analysis
The evaluated attacker is a local actor able to provide and mount an EROFS image containing an LZ4 compressed pcluster that reaches the rolling decompression path.
The complete trigger normally requires mounting or controlling the backing EROFS filesystem image. This is host-admin-equivalent in the ordinary Linux mount model because EROFS does not provide general unprivileged user-namespace mounting support. Therefore HostAdminRequired is YES.
No network input directly reaches this path. A remotely delivered filesystem image would still require a privileged local service or administrator to mount it, and such a separate delivery mechanism is not evidence of direct remote reachability.
No special hardware, race condition, RCU lifetime condition, or attacker-controlled post-free reuse is involved.
4. Primitive and severity interpretation
The exact issue is an algorithmic correctness mismatch. EROFS rolling decompression assumes long LZ4 literal copies proceed forward so that older temporary pages can be recycled after the LZ4 rolling window advances. The upstream LZ4 implementation may select backward memmove behavior based on address ordering even where source and destination do not overlap. That invalidates the EROFS page-reuse assumption and can yield incorrect decompressed output.
This is not an active-object lifetime bug, fixed stale storage bug, UAF, refcount bug, or repeated-release case. No first lifetime operation may free an object, and no second operation mutates a dangling objects lifetime state.
PrimitiveClass is NONE. The demonstrated consequence is corrupted or incorrect data returned while reading an affected EROFS image. A privilege escalation, cross-file overwrite, kernel-memory disclosure, arbitrary write, or crash is speculative and is not supported by the supplied patch.
ImportantCandidate is NO because no meaningful exploitation primitive beyond filesystem data correctness is established. AutoDowngradeAllowed is YES because there is no unresolved kernel corruption, ownership-boundary, authorization, or lifetime primitive that would be lost by ordinary low-priority handling.
Likely operational severity is low. Systems relying on EROFS image integrity should apply the correction for correctness and reliability, especially where EROFS images contain system software, but the supplied evidence does not establish a security-impacting CVE primitive.
5. One-sentence report phrase
The EROFS LZ4 rolling decompression optimization can produce incorrect decompressed data because upstream LZ4 may copy long literals backward, but the patch does not establish memory corruption, privilege escalation, information disclosure, or a denial of service primitive.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
The patch documents a bounded decompression correctness failure and disables the unsafe optimization. No concrete security primitive requiring exploitation analysis is visible.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: erofs: disable LZ4 rolling decompression for now [ Upstream
Commit: ec52dfed7b14514ed97ee71161e4cf4cfe2fbff2
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ec52dfed7b14514ed97ee71161e4cf4cfe2fbff2
Changed files:
fs/erofs/decompressor.c
fs/erofs/internal.h
fs/erofs/zdata.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=ec52dfed7b14514ed97ee71161e4cf4cfe2fbff2
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98067 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98067
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:H/UI:N/S:U/C:N/I:L/A:N
The Best / paranoid CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:L/A:L
The Best / paranoid CVSS score: 3
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: 0
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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW
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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