* [CVE-2026-90434][LOW] isofs: release zisofs block pointer buffer head [ Upstream
@ 2026-09-18 8:24 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-18 8:24 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-90434
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: isofs: release zisofs block pointer buffer head [ Upstream
Commit: dbcc7d1b818162aeab2e97fd217d86546d9fde15
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dbcc7d1b818162aeab2e97fd217d86546d9fde15
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90434
Analysis date: Fri, 18 Sep 2026 04:24:29 -0400
ActionableScore: 2
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-2026-90434 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90434
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-2026-90434 LOW https://www.kernelcve.org/list/?q=CVE-2026-90434 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:N/I:N/A:H';*CWE-772;*CWE-401;CWE-404;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A resource leak in the ISO 9660 zisofs read path occurs because zisofs_fill_pages() can return success without releasing the last referenced buffer_head used while reading the compressed block pointer table. A local actor who can access a mounted zisofs image and repeatedly read affected compressed files may cause the leak to accumulate, potentially leading to memory pressure or denial of service. For the CVSS the PR:L is used because reliable triggering requires a local user or process context with access to the mounted filesystem, even though mounting an attacker controlled image may require additional administrative or automount policy conditions. The issue is not network reachable and does not provide a demonstrated confidentiality or integrity primitive. Impact is resource exhaustion and availability loss only.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) YES DISK SIMPLEFIX ERRORPATH LINUS MEMORY DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 2
* Conservative score: 2. No floor or cap changed the score.
* Raw paranoid score: 2
* Paranoid score: 2. No floor or cap changed the score.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
Positive signals:
* +1 Concrete persistent kernel resource/reference leak. The success path in `zisofs_fill_pages()` keeps the last `buffer_head` referenced because `brelse(bh)` was missing before `return 0`.
* +1 Local below-host-admin trigger. A local user or process that can read files from an already mounted zisofs ISO filesystem can reach the affected read path.
Non-awarded signals:
* RealUAF not awarded. The patch shows a missing release causing a reference leak, not post-free use.
* Concrete repeated release/refcount not awarded. There is no first release followed by a second lifetime mutation on the same dangling reference.
* Controlled reclaim not demonstrated.
* Arbitrary read or write not demonstrated.
* Confidentiality and integrity not awarded. The evidence shows a leaked `buffer_head` reference, not disclosure or unauthorized modification.
* Reliable kernel crash not awarded. The direct evidence is kmem/resource leakage, not immediate panic.
* Extra availability not awarded. Resource exhaustion is possible under sustained repeated reads, but no immediate or broad host-wide exhaustion primitive is established.
* Remote reachability not established. This is a local filesystem read path.
* Rare subsystem penalty not applied. ISO/zisofs is optional, but optional filesystem support alone is not a concrete negative signal under the rules.
3. Reachability analysis
The vulnerable operation is reached through reading compressed zisofs data from a mounted ISO 9660 filesystem. A local user with read access to affected files can trigger the leak repeatedly. Creating or mounting an attacker-controlled ISO image may require administrative privileges or an automount policy, but the vulnerable read path itself does not require host-admin privileges once the filesystem is mounted and accessible.
There is no network trigger. No namespace-scoped privilege is involved. No special hardware is required. No race or timing dependency is present.
4. Primitive and severity interpretation
The exact primitive is a missing `brelse()` on the success path, causing a persistent `buffer_head` reference leak. This is a resource/lifetime management bug, not memory corruption.
The affected object is a kernel buffer cache object reference, but the stale object is not used after free. There is no active structured UAF, no fixed stale storage access, and no second lifetime/refcount mutation through a dangling reference.
PrimitiveClass is CLASS_C because the demonstrated behavior is resource leakage with potential DoS by accumulation, without an independently useful corruption or authorization primitive.
ImportantCandidate is NO because there is no UAF, no write primitive, no security-boundary bypass, no COW/ownership violation, no demonstrated LPE, and no unresolved exploitation leverage beyond resource exhaustion.
AutoDowngradeAllowed is YES because this is a constrained resource/reference leak with no meaningful corruption primitive and no manual-review-preserving signal.
Likely operational severity is low to ordinary moderate. Systems that automatically mount untrusted ISO images or allow many repeated reads of attacker-provided zisofs media may see higher practical DoS relevance, but the patch does not support Important-class treatment.
5. One-sentence report phrase
A missing `brelse(bh)` in the zisofs success path can leak the last `buffer_head` reference during compressed ISO reads, allowing a local reader of a mounted affected filesystem to accumulate kernel resource leaks and potentially cause resource-exhaustion DoS.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
Reason: the patch establishes a concrete resource/reference leak only, with no UAF, no repeated release, no corruption primitive, no network exposure, and no confidentiality or integrity impact.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: isofs: release zisofs block pointer buffer head [ Upstream
Commit: dbcc7d1b818162aeab2e97fd217d86546d9fde15
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dbcc7d1b818162aeab2e97fd217d86546d9fde15
Changed files:
fs/isofs/compress.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=dbcc7d1b818162aeab2e97fd217d86546d9fde15
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90434 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90434
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:L
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 4.7
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: 2
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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