[CVE-2026-46155][IMPORTANT] smb/client: fix out-of-bounds read in smb2_compound_op()

[CVE-2026-46155][IMPORTANT] smb/client: fix out-of-bounds read in smb2_compound_op()

[AL-KERNEL]

CVE: CVE-2026-46155
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: smb/client: fix out-of-bounds read in smb2_compound_op()
Commit: dffb44b2e06a2908e249f0f93156fc987eee1d1c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dffb44b2e06a2908e249f0f93156fc987eee1d1c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46155
Analysis date: Thu, 28 May 2026 12:01:12 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A malicious SMB server can send a truncated WSL EA response with an oversized `OutputBufferLength`, causing the SMB client to read beyond the response iov and potentially disclose adjacent kernel heap data or crash.

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

The original Linux kernel CVE announcement for CVE-2026-46155 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46155

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: IMPORTANT
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-2026-46155	IMPORTANT	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:H';CWE-125;CWE-126;*CWE-200;*CWE-20;Other CVSS 'AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:N/A:H';BEST CVSS score: '8.1';DESCR 'A malicious SMB server can send a truncated WSL EA response with a large OutputBufferLength so the validation succeeds but smb2_compound_op copies more bytes than the response iov contains. This can make the SMB client read beyond the rsp_iov allocation and copy adjacent kernel heap bytes, causing possible information disclosure or client kernel crash. For the CVSS the PR:N is used because the attacker only needs control of the SMB server response, while the victim must connect to that server and trigger a WSL EA query. The issue is network reachable from a malicious or compromised SMB server, but it is not a generic Internet packet path. Impact is kernel information disclosure and denial of service, with no supported write primitive or direct privilege escalation path.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) 	MAYBE	OOB DISK SIMPLEFIX LEAK SERVERTOCLIENT  KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	-	-	checked

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

ActionableScore=7
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: 6
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2. A malicious or compromised SMB server can send the crafted response.
* Weak memory corruption / invalid read primitive: +1. The client can read beyond the response iov allocation.
* Reliable kernel crash / strong DoS: +1. OOB reads from adjacent heap memory can fault or destabilize the client.
* Confidentiality impact plausible: +1. Adjacent kernel heap bytes can be copied into `idata->wsl.eas`.
* Common networking / storage path: +1. SMB client is a common network filesystem path.
* User interaction required / trust setup: -1. The victim must connect to or use the malicious server and trigger a WSL EA query.

Paranoid additional signal:

* High confidentiality concern: +1. Because the OOB bytes are copied into a client buffer, the server-controlled response path may create a practical kernel heap disclosure if that data is later observable or returned through the operation.

Not counted:

* No OOB write.
* No arbitrary write.
* No UAF or double free.
* No direct privilege escalation primitive.

## 3. Reachability analysis

The attacker controls an SMB server or compromises one that the victim mounts or accesses. The victim must perform an operation that triggers `SMB2_OP_QUERY_WSL_EA`.

This is network-reachable in the client/server trust model, but it is not a generic unsolicited packet attack against a listening kernel service. No local privileges on the victim are required from the server-side attacker.

## 4. Severity interpretation

This is at least actionable Moderate and a Strong Important candidate for SMB-client deployments that mount untrusted servers. The realistic impact is kernel heap information disclosure and possible client crash.

It does not currently support an Important LPE classification, because the patch shows an OOB read and copy, not a write primitive or object lifetime corruption.

## 5. One-sentence report phrase

A malicious SMB server can send a truncated WSL EA response with an oversized `OutputBufferLength`, causing the SMB client to read beyond the response iov and potentially disclose adjacent kernel heap data or crash.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This is network-supplied data causing a kernel heap OOB read in the SMB client, with plausible information disclosure.

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

Patch: smb/client: fix out-of-bounds read in smb2_compound_op()
Commit: dffb44b2e06a2908e249f0f93156fc987eee1d1c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dffb44b2e06a2908e249f0f93156fc987eee1d1c

Commit description:

If a server sends a truncated response but a large OutputBufferLength, and
terminates the EA list early, check_wsl_eas() returns success without
validating that the entire OutputBufferLength fits within iov_len.

Then smb2_compound_op() does:
    memcpy(idata->wsl.eas, data[0], size[0]);

Where size[0] is OutputBufferLength. If iov_len is smaller than size[0],
memcpy can read beyond the end of the rsp_iov allocation and leak adjacent
kernel heap memory.

Link: https://lore.kernel.org/linux-cifs/d998240c-aca9-420d-9dbd-f5ba24af19e0@chenxiaosong.com/
Fixes: ea41367 ("smb: client: introduce SMB2_OP_QUERY_WSL_EA")
Cc: stable@vger.kernel.org
Signed-off-by: Zisen Ye <zisenye@stu.xidian.edu.cn>
Reviewed-by: ChenXiaoSong <chenxiaosong@kylinos.cn>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/smb/client/smb2inode.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=dffb44b2e06a2908e249f0f93156fc987eee1d1c

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

The original Linux kernel CVE announcement for CVE-2026-46155 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46155

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:N/AC:H/PR:N/UI:R/S:U/C:H/I:N/A:H
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:R/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: 6
  Paranoid ActionableScore: 7

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).