* [CVE-2026-90270][MODERATE REGULAR] arm_mpam: Disable driver unbind to avoid UAF [ Upstream
@ 2026-09-17 19:41 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-17 19:41 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-90270
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: arm_mpam: Disable driver unbind to avoid UAF [ Upstream
Commit: 7d199b6a0651abad3ca6d0877dbedbe8fe6ea9e2
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7d199b6a0651abad3ca6d0877dbedbe8fe6ea9e2
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90270
Analysis date: Thu, 17 Sep 2026 15:41:41 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90270 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90270
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-2026-90270 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-90270 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:H/I:H/A:H';*CWE-416;*CWE-664;*CWE-672;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 'A use after free can occur in the ARM MPAM resctrl path when an MSC device is unbound and it is the last MSC backing a component. The mpam_component may be freed, but a later read of the resctrl schemata file can still reach resctrl_arch_get_config and access the freed component. For the CVSS the PR:L is used for the paranoid view because reliable triggering normally needs local control over the sysfs unbind path, and in some deployments this control may be available to a reduced capability root, service account, or delegated management context rather than full host administration. The issue is not network reachable. Impact is at least local denial of service via kernel crash, and because the bug class is a kernel use after free it may also require review for possible confidentiality, integrity, or privilege escalation impact.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) YES UAF HARDWARE INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 YES NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=2
ActionableScoreLower=1
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 1
* Conservative score: 1. No floor applied because host-admin-equivalent sysfs driver unbind is the only established trigger.
* Raw paranoid score: 2
* Paranoid score: 2. No UAF floor 5 applied because no concrete repeated release/refcount mutation, controlled reclaim, or meaningful reuse primitive is established.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
Positive signals:
* +2 Real UAF / lifetime violation. The commit directly states that unbinding the last MSC for a component frees `mpam_component`, and a later resctrl `schemata` read can access it through `resctrl_arch_get_config()`.
* +1 Reliable kernel crash / strong DoS. A post-free access in kernel code can plausibly fault or trigger KASAN/Oops, giving local DoS.
Negative signals:
* -2 Conservative privilege penalty. The only described trigger is the platform-driver sysfs `unbind` interface, which is host device-management control and normally host-admin-equivalent.
* -1 Paranoid privilege penalty. The supplied hint mentions possible reduced/delegated management contexts, so the paranoid view treats this as potentially below full host administration but still not ordinary unprivileged access.
Important non-awarded signals:
* Controlled reclaim not demonstrated.
* Arbitrary or directed kernel write not demonstrated.
* Confidentiality and integrity impact not awarded. The evidence supports UAF and crash risk, but not disclosure, controlled object replacement, or a write primitive.
* Remote reachability not established.
* Namespace-scoped privilege not established.
* Structured stale-object leverage not awarded. The stale object is structured, but the stale path shown is a later resctrl read, not attacker-shaped replacement or callback/ops consumption.
* Weak LPE not awarded solely because this is a UAF.
* Extra Availability not awarded because the same crash/DoS is already counted once.
* Concrete repeated release/refcount signal not awarded:
* First release can end lifetime: yes, unbinding the last MSC can free the component.
* Exact same reference survives: stale component reference is implied.
* Second operation is a real lifetime/refcount mutation: no, the later operation is described as an access/read path, not a second put/release/free/refcount mutation.
* +1 Concrete repeated release/refcount awarded: no.
* Paranoid repeated-refcount leverage awarded: no.
* FLOOR 5 applied: no.
3. Reachability analysis
The established trigger is local sysfs driver unbind of the ARM MPAM MSC platform driver, followed by reading the resctrl `schemata` file. The unbind interface is the only described way to invoke driver removal because the MPAM driver is not a module.
Ordinary unprivileged reachability is not established. The platform-driver `unbind` path is normally writable only by host administrator level users or equivalent device-management processes. The supplied hint suggests possible reduced or delegated management contexts, but that is deployment-specific and not enough to prove ordinary unprivileged reachability.
Namespace-scoped privilege is not established. This is not a network namespace, CAP_NET_ADMIN, or attacker-created namespace path. No network trigger exists. Prior setup requires an ARM MPAM-capable system with the MPAM/resctrl path active. This is hardware and platform specific, but no separate rare-hardware penalty is applied beyond the already strong privilege restriction.
No race is required. The described sequence is ordered: unbind last MSC, free component, later read schemata.
4. Primitive and severity interpretation
The exact primitive is a kernel use-after-free of `mpam_component` after driver unbind removes the last MSC backing a component. The stale object is an active structured kernel object rather than a fixed DMA buffer. The demonstrated stale use is a later resctrl configuration read through `resctrl_arch_get_config()`.
This is CLASS_B because a real kernel lifetime violation exists, but the supplied evidence does not establish controlled reclaim, attacker-controlled replacement contents, arbitrary read/write, callback control, refcount takeover, or a concrete second lifetime mutation. The demonstrated consequence is local kernel crash/DoS. Privilege escalation is a speculative consequence only and is not supported strongly enough for Class A or ImportantCandidate.
ImportantCandidate=NO because the only established complete trigger is host-admin-equivalent driver unbind or possibly delegated management, and the stale use appears constrained to a post-unbind resctrl read without demonstrated exploitation leverage beyond crash.
AutoDowngradeAllowed=YES because this is a constrained Class B UAF with crash/DoS as the demonstrated result, no concrete repeated release/refcount mutation, no security-boundary bypass, and no controlled corruption primitive.
Likely operational severity is ordinary Moderate for kernel CVE triage, with manual review recommended mainly because the root bug class is UAF.
5. One-sentence report phrase
ARM MPAM driver unbind can free the last MSC backed mpam_component while resctrl schemata access can later dereference it, causing a local use after free and likely kernel crash when host administrator or delegated device management access can trigger the unbind path.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Reason: real kernel UAF is established, but current evidence supports a constrained local/admin-triggered DoS rather than a demonstrated privilege escalation or stronger corruption primitive.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: arm_mpam: Disable driver unbind to avoid UAF [ Upstream
Commit: 7d199b6a0651abad3ca6d0877dbedbe8fe6ea9e2
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7d199b6a0651abad3ca6d0877dbedbe8fe6ea9e2
Changed files:
drivers/resctrl/mpam_devices.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=7d199b6a0651abad3ca6d0877dbedbe8fe6ea9e2
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90270 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90270
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: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: 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: 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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