* [CVE-2026-90435][MODERATE 7.0] RDMA/mlx5: Fix integer overflow of user QP buffer size [ Upstream
@ 2026-09-18 6:53 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-18 6:53 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-90435
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: RDMA/mlx5: Fix integer overflow of user QP buffer size [ Upstream
Commit: ccce6b7ef1d7efc59ccba3421e1339c6e63a3d20
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ccce6b7ef1d7efc59ccba3421e1339c6e63a3d20
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90435
Analysis date: Fri, 18 Sep 2026 02:53:04 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90435 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90435
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-2026-90435 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-90435 CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-190;CWE-680;*CWE-787;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 'An integer overflow in RDMA/mlx5 user QP buffer size calculation can make ib_umem_get() map a buffer smaller than the size later used by the hardware. A local user with access to the mlx5 RDMA uverbs device can provide large rq wqe_cnt or shift values so the signed shift or size addition wraps and produces an incorrect small buffer size. This can lead to out of bounds hardware writes and memory corruption rather than a pure warning or resource leak. For the CVSS the PR:L is used because triggering requires a local process with access to the RDMA userspace verbs interface, not full administrative privileges. The issue is not directly network reachable. Impact is at least local denial of service and in the paranoid case may include confidentiality and integrity impact due to DMA backed memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate (with actual score 7) YES SIMPLEFIX NETWORK HARDWARE KPANIC INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4 KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHERTHAN5 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=7
ActionableScoreLower=6
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
1. ActionableScore
* Raw conservative score: 6
* Conservative score: 6. No floor or cap changed the conservative score.
* Raw paranoid score: 7
* Paranoid score: 7. No floor or cap changed the paranoid score.
* Final recommended bucket: **Strong Important candidate**::
2. Signal breakdown
Positive signals:
* +2 Strong corruption primitive. User supplied rq.wqe_cnt and rq.wqe_shift can overflow signed integer buffer size calculations, causing ib_umem_get() to map a smaller buffer than the hardware later writes into.
* +1 Local below host admin reachability. The affected path is user QP creation through the RDMA mlx5 userspace verbs interface, normally reachable by a local process with access to the uverbs device rather than requiring host root.
* +1 Local high control kernel device API. The attacker controlled QP parameters directly influence WQE counts, shifts, offsets, and the size relationship between mapped memory and hardware access.
* +1 Reliable crash or strong DoS. A too small DMA or umem mapping relative to later hardware writes can plausibly trigger device faults, memory corruption, or kernel crash.
* +1 Memory layout invariant restoration. The patch restores consistency between computed RQ size, SQ size, combined QP buffer size, and qp->sq.offset before user memory is mapped.
* Paranoid additional +1 Integrity plausible. The hardware write can go beyond the intended mapped QP buffer, so unauthorized corruption outside the intended object is technically defensible even though exact target control is not demonstrated.
Non-awarded or limited signals:
* RealUAF not awarded. This is integer overflow leading to undersized mapping and possible OOB hardware write, not a lifetime or stale pointer bug.
* Controlled reclaim not demonstrated.
* Arbitrary or directed kernel write not demonstrated.
* Confidentiality impact not awarded because no read back or disclosure path is established.
* Remote reachability not awarded because the trigger is local RDMA userspace verbs access, not network packet processing.
* Namespace scoped privilege not awarded because the complete RDMA uverbs trigger is not shown to be namespace created or namespace scoped.
* Extra availability not awarded beyond the crash or corruption based DoS signal.
* Strong LPE bonus beyond the corruption primitive is not separately awarded because no credential overwrite, controlled target, or demonstrated privilege escalation chain is supplied.
3. Reachability analysis
The evaluated attacker is a local user or local process with access to the mlx5 RDMA userspace verbs device, for example /dev/infiniband/uverbsX. The vulnerable values are user supplied during user QP creation and affect the computed RQ and SQ buffer sizes.
Host administrator privilege is not positively required for the trigger once the RDMA device is available to the user. This is not an ordinary network remote attack. It also is not proven to be namespace scoped, because the supplied evidence does not show that an attacker can create all required RDMA device state inside an attacker controlled namespace.
Prior setup exists in the practical sense that mlx5 RDMA hardware, the driver, and uverbs device access must be present. That is an environmental prerequisite, not evidence that the exploit operation itself requires host admin. No race is required. The bug is an ordered validation and arithmetic failure in the QP creation path.
4. Primitive and severity interpretation
The exact primitive is signed integer overflow in QP buffer size and offset calculations. The overflow can make the kernel map or pin a buffer smaller than the size later used by the hardware. This creates an out of bounds hardware write risk through a device DMA or device access path.
This is active device managed memory state, not fixed stale storage and not cleanup only behavior. There is no concrete repeated release or refcount operation. There is no first lifetime ending operation and second stale lifetime mutation.
PrimitiveClass is CLASS_A because an attacker influenced OOB write primitive is directly supported by the patch context. The demonstrated consequence is at least local DoS or kernel memory corruption risk. The speculative but technically defensible consequence is stronger integrity impact from DMA backed memory corruption. Complete privilege escalation is not demonstrated, but the primitive is strong enough that automatic downgrade would be unsafe.
ImportantCandidate is YES because the patch establishes a concrete corruption primitive, not merely a warning, leak, or crash only invalid state. AutoDowngradeAllowed is NO because the established undersized mapping plus later hardware write leaves meaningful exploitation leverage unresolved.
Likely operational severity is Important candidate for systems exposing mlx5 RDMA uverbs access to non administrator users.
5. One-sentence report phrase
An integer overflow in RDMA mlx5 user QP buffer size calculation can cause ib_umem_get() to map a buffer smaller than the hardware later writes into, allowing a local uverbs user to trigger DMA backed out of bounds memory corruption or kernel DoS.
6. Manual review recommendation
MANUAL CHECK REQUIRED
The bug establishes a concrete attacker influenced integer overflow leading to undersized memory mapping and possible hardware out of bounds writes, so it should not be treated as ordinary DoS or automatically closed without review.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: RDMA/mlx5: Fix integer overflow of user QP buffer size [ Upstream
Commit: ccce6b7ef1d7efc59ccba3421e1339c6e63a3d20
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ccce6b7ef1d7efc59ccba3421e1339c6e63a3d20
Changed files:
drivers/infiniband/hw/mlx5/qp.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=ccce6b7ef1d7efc59ccba3421e1339c6e63a3d20
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90435 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90435
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:L/UI:N/S:U/C:L/I:L/A:H
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
The Best / paranoid CVSS score: 7.8
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: 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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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