* [CVE-2026-90284][MODERATE 7.0] firmware_loader: do not queue completed sysfs fallback requests [ Upstream
@ 2026-09-18 1:51 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-18 1:51 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-90284
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: firmware_loader: do not queue completed sysfs fallback requests [ Upstream
Commit: c8b97c5130f27b64fa2cfe1aa4bebb13f724c6c7
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c8b97c5130f27b64fa2cfe1aa4bebb13f724c6c7
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90284
Analysis date: Thu, 17 Sep 2026 21:51:35 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90284 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90284
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-2026-90284 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-90284 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:H/I:H/A:H';CWE-362;*CWE-416;CWE-667;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in the firmware_loader sysfs fallback path can queue a firmware request after it has already been completed by userspace. device_add exposes the loading attribute before fw_priv is linked into pending_fw_head, so a userspace helper can write 0 to loading and cause fw_state_done to run first. The later unconditional list_add can leave pending_fw_head containing an already completed fw_priv and after release this may become a stale pointer to freed memory. The next fallback request can fault while validating the list, giving at least a local denial of service. For the CVSS the PR:L is used for the paranoid score because a local user or service account may be able to influence firmware fallback handling through the sysfs loading interface in some deployments, although reliable triggering usually depends on local firmware helper behavior. The issue is not network reachable. Impact is at least local denial of service and in worst case may allow confidentiality or integrity impact due to use-after-free memory corruption, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) YES LOCK DANGER UAF HARDWARE LINUS BOOT KPANIC NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
1. ActionableScore
* Raw conservative score: 3
* Conservative score: 4
* Applied conservative floor: Real UAF floor 4 applies because a stale fw_priv can remain in pending_fw_head after object release, and host-admin-equivalent privilege is not positively established.
* Raw paranoid score: 4
* Paranoid score: 5
* Applied paranoid floor: Floor 5 applies because this is an active global-list lifetime violation where userspace completion can race publication and later fallback handling traverses stale list state.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
Positive signals:
* +2 Real UAF / lifetime violation: pending_fw_head may retain a pointer to released fw_priv after an already-completed request is queued.
* +1 Reliable kernel crash / strong DoS: the commit states the next fallback request can fault while validating the list.
* +1 Paranoid attacker-influenced lifetime manipulation: userspace helper activity can complete the request through the sysfs loading attribute before pending list insertion, and this completion ordering creates the stale-list condition.
Non-awarded signals:
* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Confidentiality and integrity impact not awarded as separate ActionableScore signals because no concrete disclosure, overwrite, or privilege-escalation primitive is established.
* Concrete repeated release/refcount mutation not awarded. The patch shows stale list retention and later traversal, not a second put/release/refcount mutation on the exact same dangling reference.
* Structured stale-object leverage not separately awarded beyond the paranoid lifetime-manipulation interpretation. There is no distinct attacker-shaped replacement object or callback/ops consumption shown.
* Extra Availability not awarded because the same kernel fault is already counted as reliable DoS.
* Race penalty not applied because the evidence shows a userspace helper can observe the sysfs interface after device_add, but does not establish a rare one-shot or externally uncontrollable race.
Repeated-release/refcount check:
* First release can end lifetime: yes, the request can be released after completion.
* Exact same reference survives: pending_fw_head can retain the stale fw_priv pointer.
* Second operation is a real lifetime/refcount mutation: no, supplied evidence shows later list validation/fault, not a second release/refcount operation.
* Concrete repeated release/refcount +1 awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied: yes, but due to active global-list UAF surface in the paranoid interpretation, not due to repeated refcount mutation.
3. Reachability analysis
The trigger is local through firmware_loader sysfs fallback handling. The vulnerable interleaving requires a firmware fallback request, device_add exposing the loading attribute, and a userspace helper writing 0 before fw_priv is inserted into pending_fw_head.
The complete privilege boundary is not fully resolved from the supplied patch. Firmware fallback sysfs attributes and firmware request initiation are often controlled by privileged firmware helper infrastructure, but the supplied evidence does not positively establish that host-admin-equivalent privilege is required for the full vulnerable sequence. Therefore HostAdminRequired is UNKNOWN, not YES.
There is no evidence that the complete trigger is namespace-scoped. NamespaceScopedPrivilege is NO.
No direct network reachability is established. No special hardware requirement is established beyond a code path that uses firmware sysfs fallback. The race is specific but appears tied to normal userspace helper ordering rather than a proven rare hardware timing window.
4. Primitive and severity interpretation
The exact primitive is a race-induced stale list entry: fw_load_sysfs_fallback publishes the sysfs loading interface before fw_priv is linked into pending_fw_head. If userspace completes the request first, fw_state_done cannot remove it from pending_fw_head because it was not queued yet. The later unconditional list_add can queue an already-completed fw_priv. After release, pending_fw_head may contain a pointer to freed memory.
This is an active structured lifetime bug rather than fixed stale storage. The stale state is a global pending request list entry that later fallback handling can traverse. The demonstrated consequence is a kernel fault during later list validation, i.e. local DoS.
A concrete repeated release/refcount operation is not established. This is not CLASS_A because controlled reclaim, directed write, callback control, refcount takeover, or demonstrated LPE is not shown. It is CLASS_B because a real kernel lifetime/UAF primitive exists and the post-lifetime list state leaves unresolved exploitation leverage beyond a simple NULL dereference.
ImportantCandidate is YES because a real active-list UAF remains unresolved and should not be automatically treated as ordinary crash-only behavior. AutoDowngradeAllowed is NO because automatic closure would discard a concrete stale global-list lifetime primitive that requires manual exploitation-leverage review.
5. One-sentence report phrase
A race in firmware_loader sysfs fallback can queue an already completed fw_priv into pending_fw_head, leaving a stale pointer after release and causing at least a local kernel crash on later fallback list validation.
6. Manual review recommendation
MANUAL CHECK REQUIRED
Reason: real UAF / stale global-list lifetime violation is established, and although only DoS is demonstrated, the active list corruption surface requires manual review before downgrade.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: firmware_loader: do not queue completed sysfs fallback requests [ Upstream
Commit: c8b97c5130f27b64fa2cfe1aa4bebb13f724c6c7
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c8b97c5130f27b64fa2cfe1aa4bebb13f724c6c7
Changed files:
drivers/base/firmware_loader/fallback.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=c8b97c5130f27b64fa2cfe1aa4bebb13f724c6c7
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90284 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90284
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:H/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
The Best / paranoid CVSS score: 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: 4
Paranoid ActionableScore: 5
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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