[CVE-2026-97563][MODERATE 7.0] smb: client: reject out-of-bounds DataOffset in CIFSSMBRead()

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-97563
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: smb: client: reject out-of-bounds DataOffset in CIFSSMBRead()
Commit: 667feba13e78d16393aacb15869f70970f422227
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=667feba13e78d16393aacb15869f70970f422227
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97563
Analysis date: Sat, 26 Sep 2026 16:06:56 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-97563 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97563

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-2026-97563	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-97563 CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H';CWE-125;*CWE-200;*CWE-20;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H';BEST CVSS score: '8.1';DESCR 'The paranoid score uses C:H because the patch establishes a real kernel heap read primitive and repeated attacker controlled offsets may disclose substantial adjacent memory. I:N is retained because neither the diff nor the described data flow provides an out of bounds write or another integrity primitive. AV:A reflects the usual internal SMB deployment. AV:N should be considered by an analyst if the vulnerable SMB1 client can connect to an attacker controlled server across routed or public networks. The supplied commit identifier is abbreviated and no verified CVE or full patch URL was provided.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)  SKIP CVE-2026-97563 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	WRITE OOB DANGER DISK IMPROVEONLY SERVERTOCLIENT LINUS KPANIC  DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	-	-	checked

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

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

1. ActionableScore

* Raw conservative score: 4
* Conservative score: 5
* Raw paranoid score: 4
* Paranoid score: 5
* Applied conservative floor: 4 -> 5 because a concrete attacker-influenced kernel heap disclosure primitive is established and automatic closure would discard unresolved disclosure severity.
* Applied paranoid floor: 4 -> 5 for the same Class A disclosure primitive. No speculative exploitation bonus was added.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Positive signals:

* +2 Strong attacker-influenced primitive. The SMB1 server controls DataOffset and DataLength, causing memcpy to read beyond the received response and copy adjacent kernel heap into the caller buffer.
* +1 Confidentiality plausible. The out-of-bounds bytes reach a caller-visible read buffer, establishing an actual disclosure path rather than an internal invalid read.
* +1 Practical exploit chain. A malformed SMB1 read response directly selects the out-of-bounds source range and returns the copied bytes through the read operation.
* +1 Reliable kernel crash or strong DoS. An offset reaching unmapped memory can produce a kernel oops.

Negative signals:

* -1 Legacy and non-default mode. Reaching this path requires an explicit vers=1.0 mount because SMB1 is not negotiated by default.

Not awarded:

* Direct remote reachability +2 was not awarded because a separately configured SMB1 mount is a material prerequisite.
* No integrity point was awarded because the operation reads kernel memory but does not write outside its destination.
* No arbitrary write, controlled reclaim, UAF, callback influence, or privilege-escalation primitive is established.
* No additional Availability point was awarded because it would double-count the same kernel oops.
* No common networking-path or broad-default-exposure point was awarded because the affected SMB1 mode is legacy and disabled by default.
* Memory-layout invariant restoration was not scored separately because it describes the same out-of-bounds read primitive.

Arithmetic:

* Conservative: +2 +1 +1 +1 -1 = 4. Manual-review safety floor raises it to 5.
* Paranoid: +2 +1 +1 +1 -1 = 4. The same floor raises it to 5.
* Repeated requests may increase the amount of disclosed heap data, but no extra paranoid point is assigned because this does not establish a new primitive.

3. Reachability analysis

The attacker is a malicious or compromised SMB1 server that supplies a crafted synchronous read response. After the SMB1 mount exists, the server requires no privilege on the client, so HostAdminRequired is NO.

A prior explicit vers=1.0 mount is required and normally represents deliberate local setup. The supplied evidence does not show that the remote attacker can create this mount. Consequently, the vulnerability is remotely exercised only against clients already configured to use the attacker-controlled or compromised SMB1 server.

No namespace-scoped capability is needed by the server-side attacker, and namespace creation is not part of the trigger. No special hardware, sysctl, boot option, or race timing is involved. Triggering is deterministic once the vulnerable client issues a read and accepts the crafted response.

4. Primitive and severity interpretation

The exact primitive is an attacker-directed out-of-bounds kernel heap read followed by memcpy into the caller-visible read buffer. This is not a UAF, stale-object issue, lifetime violation, or write primitive.

PrimitiveClass is CLASS_A because a concrete kernel disclosure primitive is established. DataOffset selects the starting point beyond the response, while DataLength controls the amount copied within existing upper bounds. The alternative demonstrated consequence is an invalid read into unmapped memory and kernel oops.

The practical evidence supports information disclosure and DoS. It does not support integrity modification, arbitrary kernel read at an unrestricted address, arbitrary write, or privilege escalation. Repeated offsets may expose substantial adjacent heap data, but the 16-bit relative offset and current heap layout constrain address selection.

ImportantCandidate is YES because actual kernel heap bytes cross into a caller-visible buffer under server influence. AutoDowngradeAllowed is NO because reducing this to an ordinary malformed-response crash would discard the established disclosure primitive. Operational severity is Actionable Moderate at minimum, with Important classification requiring review of buffer allocation layout, readable length, mount permissions, and whether a cooperating local reader can reliably recover sensitive kernel objects.

5. One-sentence report phrase

A malicious SMB1 server can supply an unchecked DataOffset that makes CIFSSMBRead copy adjacent kernel heap into a caller-visible read buffer or access unmapped memory and crash the client kernel.

6. Manual review recommendation

MANUAL CHECK REQUIRED

The patch establishes a real kernel heap disclosure primitive, and manual analysis is needed to determine the quantity and sensitivity of recoverable data and whether the server can reliably coordinate disclosure with a local reader.

7. Call-site confidence

Call-site confidence: high

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

Patch: smb: client: reject out-of-bounds DataOffset in CIFSSMBRead()
Commit: 667feba13e78d16393aacb15869f70970f422227
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=667feba13e78d16393aacb15869f70970f422227

Commit description:

The SMB1 synchronous read helper CIFSSMBRead() validates the server's
DataLength against CIFSMaxBufSize and the caller's count, but never
validates DataOffset. The copy source is formed as

	&pSMBr->hdr.Protocol + le16_to_cpu(pSMBr->DataOffset)

and memcpy()'d for DataLength bytes with no check that the
[DataOffset, DataOffset + DataLength) range lies within the response
actually received from the server.

A malicious or compromised SMB1 server can return a response carrying
an in-range DataLength and a large DataOffset, driving the source
pointer past the end of the response buffer. The memcpy() then copies
adjacent kernel heap into the caller's read buffer (information
disclosure), or reads unmapped memory and oopses (denial of service).
SMB1 is not negotiated by default; reaching this code requires an
explicit vers=1.0 mount.

Both DataOffset and the received response length recorded in
rsp_iov.iov_len are relative to the start of the SMB header, so reject
the response unless DataOffset + DataLength fits within that length,
using overflow-safe arithmetic, before forming the source pointer.
The response length has been validated by the previous patch, so the
DataOffset and DataLength fields can be read safely here.

While here, make data_length unsigned. It holds a length derived from
unsigned on-the-wire fields and is only ever compared against unsigned
quantities; print it with %u accordingly, and add __func__ to the
cifs_dbg() calls in this function.

Fixes: 1da177e ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org # 6.19.x
Assisted-by: Bynario AI
Signed-off-by: Diego Oliva <diego@bynar.io>
Reviewed-by: David Howells <dhowells@redhat.com>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/smb/client/cifssmb.c
  fs/smb/client/trace.h

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=667feba13e78d16393aacb15869f70970f422227

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

The original Linux kernel CVE announcement for CVE-2026-97563 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97563

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:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
  The Best / paranoid CVSS score: 8.1

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: 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).