[CVE-2026-90125][LOW] smb: client: fix request buffer leak in smb2_new_read_req() [ Upstream

[CVE-2026-90125][LOW] smb: client: fix request buffer leak in smb2_new_read_req() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-90125
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: smb: client: fix request buffer leak in smb2_new_read_req() [ Upstream
Commit: 58066940076b90c16e821fd6f9767cd979cbdb5e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=58066940076b90c16e821fd6f9767cd979cbdb5e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90125
Analysis date: Thu, 17 Sep 2026 18:41:19 -0400
ActionableScore: 2
ActionableScore lower bound: 1
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-2026-90125 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90125

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-2026-90125	LOW	https://www.kernelcve.org/list/?q=CVE-2026-90125 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-401;*CWE-772;**CWE-400;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 request buffer leak exists in the SMB client async read path because smb2_new_read_req() allocates a request with smb2_plain_req_init() but can return before publishing the buffer to the caller. The practically reachable path is an SMB Direct RDMA memory registration failure in smbd_register_mr(), where -EAGAIN is returned and the caller cannot release the unpublished request buffer. Because -EAGAIN is replayable, repeated retry attempts can leak additional buffers and may eventually exhaust memory. For the CVSS the PR:L is used because a local user or local process generally must be able to issue reads through an already mounted SMB share, while mounting and RDMA transport setup are normally administrative actions. The issue is not directly network reachable as an unauthenticated packet trigger. Impact is denial of service through resource exhaustion, with no evidence of memory corruption, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	YES	READ DISK LEAK SERVERTOCLIENT LINUS 	NO	NO	checked

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

ActionableScore=2
ActionableScoreLower=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1. No floor or cap applied.
* Raw paranoid score: 2
* Paranoid score: 2. No floor or cap applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

Conservative positive signals:

* +1 Concrete persistent kernel resource/reference leak. `smb2_new_read_req()` allocates a request buffer via `smb2_plain_req_init()` and can return before assigning it to `*buf`, so the caller cannot release it.

Paranoid additional signals:

* +1 Sustained resource-exhaustion concern. The reachable `-EAGAIN` path is replayable, and the commit states that on a hard mount retries may be unbounded by `retrans`, so repeated failures can leak multiple buffers.

Non-awarded signals:

* RealUAF not awarded. The bug is a missing release of an allocated buffer, not post-free use.
* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Confidentiality and integrity not awarded. The patch supports memory/resource leakage only, not disclosure or unauthorized modification.
* Remote reachability not awarded. This is SMB client-side async read behavior, not an unauthenticated network packet trigger against the victim kernel.
* Reliable kernel crash not awarded. Memory exhaustion is possible through accumulation, but no immediate panic or deterministic crash primitive is shown.
* Extra Availability not double-counted beyond the paranoid resource-exhaustion concern.
* Race/timing penalty not applied. This is an ordered error-path leak, not a timing race.

3. Reachability analysis

The affected path is the SMB client asynchronous read path with SMB Direct RDMA memory registration. A local process that can read from an already mounted SMB share may reach the read path, but the complete practical trigger also depends on SMB Direct/RDMA being in use and on `smbd_register_mr()` failing in a replayable way. Mount creation and RDMA transport setup are normally administrative or environment-provided prerequisites, but the supplied evidence does not prove that the attacker must be host admin to trigger the leak once the mount exists. Therefore `HostAdminRequired=UNKNOWN`, not YES.

No namespace-scoped capability path is indicated. No network namespace or container-specific capability chain is relevant. Prior privileged setup may exist in practice because the SMB share and RDMA transport must already be configured. There is no special timing race. The repeated leak depends on retry behavior after `-EAGAIN`, not on catching a narrow window.

4. Primitive and severity interpretation

The exact primitive is a persistent request-buffer leak on error handling in `smb2_new_read_req()`. The affected object is allocated but neither returned to the caller nor released on the failing path. This is not active structured stale-object use, not fixed stale storage after free, and not a repeated release/refcount mutation.

Primitive class is `CLASS_C` because the demonstrated behavior is resource exhaustion / DoS without a corruption, authorization, ownership, or memory-safety primitive. The demonstrated consequence is memory leakage that may accumulate under repeated retry. The speculative consequence is broader system memory pressure or DoS if the failure repeats enough times. There is no evidence of privilege escalation, information disclosure, arbitrary write, controlled reclaim, or kernel memory corruption.

`ImportantCandidate=NO` because the issue is a resource leak with constrained prerequisites and no unresolved corruption or boundary-bypass primitive. `AutoDowngradeAllowed=YES` because automatic Important preservation would lose no concrete UAF, refcount mutation, controlled corruption, authorization bypass, or ownership violation.

5. One-sentence report phrase

An SMB client async read request buffer can be leaked when SMB Direct RDMA memory registration fails before the buffer is published to the caller, allowing repeated replayable failures to cause resource exhaustion DoS in affected configured environments.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: this is a concrete resource leak without UAF, memory corruption, authorization bypass, or demonstrated privilege-escalation path.

7. Call-site confidence

Call-site confidence: high

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

Patch: smb: client: fix request buffer leak in smb2_new_read_req() [ Upstream
Commit: 58066940076b90c16e821fd6f9767cd979cbdb5e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=58066940076b90c16e821fd6f9767cd979cbdb5e

Changed files:
  fs/smb/client/smb2pdu.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=58066940076b90c16e821fd6f9767cd979cbdb5e

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

The original Linux kernel CVE announcement for CVE-2026-90125 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90125

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: 1
  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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).