* [CVE-2026-97559][MODERATE REGULAR] smb: client: fail DACL rewrite when the new DACL exceeds 64K [ Upstream
@ 2026-09-25 11:24 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-25 11:24 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-97559
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: smb: client: fail DACL rewrite when the new DACL exceeds 64K [ Upstream
Commit: 2ef532a01f44687f5b95001e88247cf05bff9892
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2ef532a01f44687f5b95001e88247cf05bff9892
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97559
Analysis date: Fri, 25 Sep 2026 07:24:52 -0400
ActionableScore: 1
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-2026-97559 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97559
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: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-97559 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-97559 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:N/I:L/A:N';CWE-190;CWE-681;CWE-284;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N';BEST CVSS score: '3.3';DESCR 'An integer overflow in SMB client DACL rewriting can occur because the accumulated rewritten DACL size was stored in a 16 bit value. A specially shaped DACL with many ACEs can expand during SID replacement or chmod ACL rewriting and cause the size value and subsequent offsets to wrap. The resulting corrupted DACL is sent to the SMB server. The allocation covers the worst case expansion, so the patch context does not indicate an out of bounds write or other kernel memory corruption. For the CVSS the PR:L value is used because a local user or process must perform an ACL changing operation on an SMB mount. The issue is not directly network reachable from an unauthenticated remote client, although a malicious SMB server or attacker controlled share may help provide the required DACL layout. The primary impact is limited integrity impact if a server accepts and applies an incorrectly rewritten DACL. Server specific ACL validation and interpretation should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) YES WRITE OOB DANGER DISK INIT SERVERTOCLIENT LINUS DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS YES NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +1 Weak indirect structured-state corruption. A 16 bit size accumulator wraps while constructing an SMB DACL, causing incorrect DACL size and ACE offsets within an allocated buffer. The malformed DACL is transmitted to the server.
* No kernel memory-corruption score. The patch explicitly states that allocation covers the maximum possible rewritten DACL expansion, therefore this is not an out-of-bounds write.
* No UAF or lifetime signal. No freed object, stale reference, refcount misuse, or repeated release operation is established.
* No direct remote-reachability score. The vulnerable rewriting operation is initiated by the local SMB client during ACL rewrite activity. A remote server can supply DACL content, but cannot directly invoke the local chmod or chown operation without a local client-side action.
* No local-unprivileged-trigger score. The supplied patch does not establish that an ordinary unprivileged local user can complete the full trigger sequence against an affected mounted SMB object.
* No integrity-impact score. The outgoing DACL is malformed, but the supplied evidence does not establish that a server accepts it in a way that bypasses authorization or modifies ACLs beyond the authority already held by the caller.
* No strong semantic reinterpretation score. The arithmetic wrap corrupts a wire-format ACL representation, but there is no demonstrated reinterpretation of active kernel objects, memory ownership, or security-sensitive kernel state.
* No crash or availability score. The stated consequence is corrupted DACL data sent to the server, not a kernel crash, panic, hang, or resource exhaustion.
3. Reachability analysis
The immediate trigger is a local SMB client operation that rewrites a DACL, such as chmod or chown related security-descriptor handling. The source DACL must be unusually large and shaped so that SID replacement expands enough ACEs to exceed the 16 bit DACL wire-size limit. The commit identifies wraparound at approximately 863 expanded ACEs.
Host-admin-equivalent privilege is not positively established, but below-host-admin reachability is also not fully established. ACL-changing operations may be available to an ordinary owner of an SMB object, but the complete scenario also depends on SMB server ACL behavior, mount configuration, ownership, and permissions. Therefore HostAdminRequired is UNKNOWN.
No namespace-specific operation or namespace-scoped capability check is visible in the supplied context. NamespaceScopedPrivilege is UNKNOWN. There is no hardware, boot parameter, race condition, or special device prerequisite established by the patch.
4. Primitive and severity interpretation
The exact primitive is a bounded integer-overflow and malformed-output condition in SMB client DACL construction. A u16 accumulator wraps after ACE expansion, so the DACL size field and later offsets no longer describe the actual constructed ACL. The allocation remains sufficiently large, so writes remain inside the allocated buffer.
This is not an active kernel-object corruption primitive, UAF, OOB write, arbitrary write, refcount corruption, or ownership violation. The demonstrated effect is transmission of an incorrectly structured security descriptor to the SMB server. Whether this can produce a meaningful authorization or ACL-policy effect depends on server-side validation and interpretation, which are not established by the patch.
PrimitiveClass is CLASS_C because the demonstrated behavior is an invalid structured state rather than an independently useful kernel-corruption primitive. ImportantCandidate is NO because no controlled memory corruption, authorization bypass, protected-resource access, or privilege-escalation mechanism is shown. AutoDowngradeAllowed is YES because the available evidence supports a constrained malformed-DACL condition without unresolved kernel lifetime or boundary-bypass leverage.
5. One-sentence report phrase
A u16 overflow in SMB client DACL rewriting can produce a malformed ACL sent to the SMB server, but the patch establishes no out-of-bounds kernel write or direct privilege-escalation primitive.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Server-specific ACL parsing and validation should be checked to determine whether an affected SMB server can accept the malformed DACL and apply unintended access-control semantics.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: smb: client: fail DACL rewrite when the new DACL exceeds 64K [ Upstream
Commit: 2ef532a01f44687f5b95001e88247cf05bff9892
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2ef532a01f44687f5b95001e88247cf05bff9892
Changed files:
fs/smb/client/cifsacl.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=2ef532a01f44687f5b95001e88247cf05bff9892
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-97559 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97559
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:L/A:N
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
The Best / paranoid CVSS score: 3.3
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: 1
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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