* [CVE-2026-89506][MODERATE REGULAR] RDMA/uverbs: Add UVERBS_ATTR_UHW to UVERBS_METHOD_REG_MR
@ 2026-09-12 11:12 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-12 11:12 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-89506
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: RDMA/uverbs: Add UVERBS_ATTR_UHW to UVERBS_METHOD_REG_MR
Commit: 71d5c41ac583df09a7c32199bef7d42de7267d07
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=71d5c41ac583df09a7c32199bef7d42de7267d07
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89506
Analysis date: Sat, 12 Sep 2026 07:12:27 -0400
ActionableScore: 3
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89506 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89506
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: YES
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-89506 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89506 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';**CWE-476;*CWE-20;CWE-754;BEST CVSS score: '5.5';DESCR 'A NULL pointer dereference in the RDMA uverbs REG_MR path can occur because the core ioctl handler passed NULL driver udata to reg_user_mr for drivers that expect a valid udata object. A malicious local userspace process with access to an RDMA uverbs device can craft the REG_MR ioctl path and trigger a crash in affected drivers such as mthca, irdma, or siw. For the CVSS the PR:L value is selected because triggering requires local execution and access to the uverbs device, but it does not require full administrative privileges in typical RDMA deployments. The issue is not network reachable because the trigger is a local uverbs ioctl rather than remote RDMA traffic. Impact is denial of service via kernel crash. No confidentiality or integrity impact is assigned because the visible primitive is a NULL pointer dereference and not UAF, OOB access, arbitrary write, or information disclosure.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3) YES DANGER SIMPLEFIX NETWORK KERNEL_PANIC_PLUS_UAF MEMORY DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH YES NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=3
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 3
* Conservative score: 3
* Raw paranoid score: 3
* Paranoid score: 3
* Final recommended bucket: **Borderline / manual review recommended**::
No floor or cap changed the score.
2. Signal breakdown
Positive signals:
* +1 Local userspace trigger: the commit explicitly says malicious userspace could trigger the crash through the uverbs ioctl path.
* +1 Invalid kernel pointer dereference / Class C primitive: the core REG_MR handler passed NULL udata to drivers that assume udata is non-NULL.
* +1 Reliable kernel crash / strong DoS: the described result is a NULL udata crash in affected RDMA drivers.
Negative signals:
* No host-admin penalty: host-admin-equivalent privilege is not positively established. The supplied evidence says malicious userspace can trigger it.
* No rare-hardware penalty: affected drivers are specific, but the scoring rules require concrete evidence of rare or physical-only access before subtracting.
Important non-awarded signals:
* RealUAF not awarded: this is a NULL pointer dereference, not a stale post-lifetime object use.
* Controlled reclaim not demonstrated.
* Arbitrary or directed write not demonstrated.
* Confidentiality and integrity not awarded: no information disclosure, object corruption, UAF, OOB write, or authorization bypass is established.
* Remote reachability not awarded: the trigger is a local uverbs ioctl, not RDMA network traffic.
* Local high-control kernel data-plane API not awarded: userspace can craft the ioctl path, but no exploitation-relevant control over memory layout, object replacement, refcounts, callbacks, or target corruption is established.
* Extra Availability not awarded: the same kernel crash is already counted once.
* Weak LPE or strong exploitation leverage not awarded: the visible primitive is crash-only NULL dereference.
3. Reachability analysis
The evaluated attacker is a local userspace process with access to an RDMA uverbs device such as `/dev/infiniband/uverbsX`. The commit states that normal rdma-core does not hit this path, but malicious userspace can craft the ioctl path and trigger it.
Host administrator privilege is not positively required by the supplied evidence, so HostAdminRequired is NO. The trigger still depends on local device-node access or equivalent RDMA userspace access policy.
No network trigger is established. Remote RDMA traffic does not directly invoke the vulnerable REG_MR ioctl on the victim.
No namespace-scoped capability chain is established. This is a local device-interface issue, not a demonstrated namespace capability bypass.
No race is involved. No prior privileged setup beyond the existence and accessibility of the RDMA uverbs device is established in the supplied input.
4. Primitive and severity interpretation
The exact primitive is a NULL `udata` dereference in affected RDMA drivers when `UVERBS_METHOD_REG_MR` calls `reg_user_mr()` without passing valid driver udata.
This is not an active structured-object UAF and not fixed stale storage. It is a direct invalid pointer use caused by missing ioctl attribute plumbing.
There is no concrete repeated release or refcount operation. There is no first release that may end lifetime, no surviving dangling reference, and no second lifetime mutation.
PrimitiveClass is CLASS_C because the demonstrated behavior is crash/DoS from invalid state without an independently useful corruption primitive.
The demonstrated consequence is local denial of service via kernel crash. A stronger consequence such as privilege escalation is speculative and unsupported by the patch and supplied context.
ImportantCandidate is NO because no Class A primitive and no strong unresolved Class B lifetime/corruption primitive is established.
AutoDowngradeAllowed is YES because this is a constrained crash-only NULL dereference with no UAF, no repeated lifetime mutation, no controlled corruption, and no security-boundary bypass.
Likely operational severity is ordinary to borderline Moderate. It should be reviewed for exposure where untrusted users have RDMA uverbs access, but it does not look like an Important-class kernel vulnerability from the supplied evidence.
5. One-sentence report phrase
A malicious local userspace process with access to an RDMA uverbs device can trigger a NULL udata dereference in selected REG_MR driver paths, causing a kernel crash and local denial of service without evidence of privilege escalation or remote reachability.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Reason: local userspace can trigger a kernel crash through a device interface, but the established primitive is NULL dereference only and does not show memory corruption, UAF, authorization bypass, or LPE.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: RDMA/uverbs: Add UVERBS_ATTR_UHW to UVERBS_METHOD_REG_MR
Commit: 71d5c41ac583df09a7c32199bef7d42de7267d07
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=71d5c41ac583df09a7c32199bef7d42de7267d07
Commit description:
The original commit missed that three drivers (mthca, irdma, siw) have UHW
data associated with reg_mr that cannot be passed through the ioctl. They
also assume that the udata cannot be NULL, so failing to pass a valid
udata can trigger a NULL udata crash in those drivers.
This never happens in real systems since in rdma-core ibv_cmd_reg_mr_ex()
does not accept a udata and those three drivers don't use it, however a
malicious userspace could trigger it.
Cc: [email protected]
Fixes: 5b2e450 ("IB/core: Add UVERBS_METHOD_REG_MR on the MR object")
Reported-by: Jacob Moroni <[email protected]>
Closes: https://lore.kernel.org/all/CAHYDg1TOGxRGZrS69d4Y--Shj_DZv0nJuM73iHUBwBM70g_t3Q@mail.gmail.com
Signed-off-by: Jason Gunthorpe <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
drivers/infiniband/core/uverbs_std_types_mr.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=71d5c41ac583df09a7c32199bef7d42de7267d07
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89506 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89506
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: Not available
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 5.5
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: 3
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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