[CVE-2026-90416][MODERATE REGULAR] RDMA/mlx5: Fix stack out-of-bounds read in cc_params debugfs [ Upstream

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

CVE: CVE-2026-90416
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: RDMA/mlx5: Fix stack out-of-bounds read in cc_params debugfs [ Upstream
Commit: 1c5b4f76cd73372c5a8a4c91c95d5a31f141e091
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1c5b4f76cd73372c5a8a4c91c95d5a31f141e091
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90416
Analysis date: Fri, 18 Sep 2026 01:23:04 -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-2026-90416 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90416

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-2026-90416	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-90416 CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N';CWE-126;*CWE-200;CWE-193;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '3.3';DESCR 'A stack out of bounds read in RDMA/mlx5 debugfs get_param() can occur because a u32 congestion parameter was formatted as a signed decimal string into an 11 byte stack buffer. A value with bit 31 set can produce a longer string than the buffer can fully store, while the returned length can still make simple_read_from_buffer read one byte past lbuf. This can expose one byte of kernel stack memory to a local reader of the debugfs parameter. For the CVSS the PR:L is used in the paranoid score when debugfs or this mlx5 debugfs file is readable by a less privileged local user, while the typical deployment may require administrator level debugfs access. The issue is not network reachable and does not provide a write primitive. Impact is limited confidentiality exposure, with no direct integrity or availability impact indicated by the code path.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	YES	WRITE OOB SIMPLEFIX LEAK NETWORK DEBUGFS LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	NO	NO	checked

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

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

1. ActionableScore

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

2. Signal breakdown

Positive signals:

* +1 Confidentiality plausible: the one byte stack out-of-bounds read is passed to simple_read_from_buffer(), so a local reader of the debugfs file can receive one byte beyond lbuf.

Negative or non-awarded signals:

* +0 Real UAF not awarded: no lifetime violation, stale pointer, refcount issue, or double release is established.
* +0 Strong corruption not awarded: this is read-only stack OOB, not an OOB write, UAF, controlled reclaim, or arbitrary write.
* +0 Strong LPE not awarded: no privilege escalation primitive is shown.
* +0 Integrity not awarded: no write or unauthorized modification path is shown.
* +0 Availability not awarded: no crash, panic, hang, or resource exhaustion is established.
* +0 Local unprivileged trigger not awarded: the supplied context does not prove that ordinary unprivileged users can read this mlx5 debugfs file.
* +0 Host-admin penalty not applied: host-admin-equivalent access is also not positively established from the supplied evidence.
* +0 Hardware rarity penalty not applied: mlx5/RDMA hardware is device-specific, but the prompt requires concrete evidence of rare or physical-only access before subtracting points.
* No repeated release/refcount analysis applies: there is no first release, no surviving exact reference, and no second lifetime mutation.

3. Reachability analysis

The vulnerable path is a debugfs read handler in drivers/infiniband/hw/mlx5/cong.c. The attacker must be able to read the affected mlx5 congestion-control debugfs parameter and must have a device/configuration where mlx5_ib_get_cc_params() can return a u32 value whose signed formatting would exceed the 11 byte stack buffer.

The complete privilege boundary is not resolved by the supplied patch. Debugfs is often restricted in production deployments, but the exact file mode and mount policy are not shown. Therefore HostAdminRequired is UNKNOWN rather than YES or NO.

There is no namespace-scoped privilege evidence. The issue is local only and is not network reachable merely because RDMA hardware is involved. No race is involved, and no special timing condition is required once the file is readable.

4. Primitive and severity interpretation

The exact primitive is a bounded stack out-of-bounds read of one byte. It occurs because snprintf() returns the full length that would have been written, while the fixed 11 byte stack buffer stores fewer bytes. simple_read_from_buffer() then uses the returned length and can copy one byte past lbuf to userspace.

This is not an active structured-object UAF and not fixed stale storage. It is a local information disclosure primitive with very limited size. The demonstrated consequence is one byte of kernel stack disclosure. The speculative consequence is that repeated reads might expose small adjacent stack bytes if the surrounding stack layout and value conditions are favorable, but the patch does not support arbitrary read, write, code execution, or privilege escalation.

PrimitiveClass is CLASS_C because this is a weak read-only invalid access with limited disclosure and no meaningful corruption or lifetime primitive. ImportantCandidate is NO because the issue lacks UAF, write corruption, controlled reclaim, authorization bypass, or a practical LPE chain. AutoDowngradeAllowed is YES because the established impact is limited local information disclosure and no unresolved Important-grade primitive remains.

5. One-sentence report phrase

A local stack out-of-bounds read in RDMA/mlx5 debugfs get_param() can leak one byte of kernel stack memory through simple_read_from_buffer() when a u32 congestion parameter is formatted with an undersized signed decimal buffer.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: this is a real kernel stack information leak copied to userspace, but the leak is limited to one byte and the supplied evidence does not show a stronger primitive or broad unprivileged reachability.

7. Call-site confidence

Call-site confidence: high

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

Patch: RDMA/mlx5: Fix stack out-of-bounds read in cc_params debugfs [ Upstream
Commit: 1c5b4f76cd73372c5a8a4c91c95d5a31f141e091
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1c5b4f76cd73372c5a8a4c91c95d5a31f141e091

Changed files:
  drivers/infiniband/hw/mlx5/cong.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=1c5b4f76cd73372c5a8a4c91c95d5a31f141e091

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

The original Linux kernel CVE announcement for CVE-2026-90416 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90416

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:L/PR:H/UI:N/S:U/C:L/I:N/A:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).