* [CVE-2026-92505][LOW] iommu/amd: Fix undefined behavior in devid_write debugfs function [ Upstream
@ 2026-09-17 20:34 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-17 20:34 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-92505
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: iommu/amd: Fix undefined behavior in devid_write debugfs function [ Upstream
Commit: 8aabe0fba01486b5d893e708b05a8fa7f1b7efbb
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8aabe0fba01486b5d893e708b05a8fa7f1b7efbb
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-92505
Analysis date: Thu, 17 Sep 2026 16:34:37 -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-2026-92505 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-92505
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: LOW
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-2026-92505 LOW https://www.kernelcve.org/list/?q=CVE-2026-92505 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:L/I:N/A:L';CWE-758;CWE-125;*CWE-20;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.4';DESCR 'The AMD IOMMU debugfs devid_write handler could access pci_seg id after a failed PCI segment lookup, where pci_seg no longer refers to a valid segment object. This is an invalid read and undefined behavior in a local debugfs write path, but the patch does not show an arbitrary write, UAF, or direct information disclosure primitive. For the CVSS the PR:L value is used only for the paranoid interpretation where a reduced privilege local user or service has delegated write access to the relevant debugfs file. In typical deployments this path is restricted to administrator level access, so practical exposure is low. The issue is not network reachable. Impact is mainly limited to local denial of service or minor confidentiality concern from an invalid kernel read, with no strong evidence of privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) YES SIMPLEFIX HARDWARE DEBUGFS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS_AND_CIANNH YES NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
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
* +1 Weak / indirect corruption candidate. The patch shows an invalid object pointer interpretation after `for_each_pci_segment()` completes without a match. `pci_seg` may refer to the list head rather than a valid PCI segment, and `pci_seg->id` is then read.
* +0 Reliable kernel crash not awarded. The commit says undefined behavior, but no concrete panic, Oops, UAF, write, or fatal fault is demonstrated.
* +0 Real UAF not awarded. No freed object or post-lifetime use is established.
* +0 Concrete repeated release/refcount not awarded. There is no first release, surviving dangling reference, or second lifetime mutation.
* +0 Confidentiality not awarded. The invalid read is internal and no user-visible disclosure path is shown.
* +0 Integrity not awarded. No unauthorized write, persistent state corruption, or security-boundary modification is shown.
* +0 Remote reachability not awarded. This is a local AMD IOMMU debugfs write path.
* No negative privilege penalty applied. Debugfs write access is typically administrator-controlled, but the supplied context does not show the exact file mode or complete privilege check, so host-admin-equivalent requirement is not scored as established.
* No paranoid uplift applied. The stronger interpretation remains an invalid read / undefined behavior without UAF, controlled corruption, authorization bypass, or demonstrated DoS.
3. Reachability analysis
The vulnerable path is `devid_write()` in `drivers/iommu/amd/debugfs.c`, reached through a local debugfs write interface. The input can select a segment/device id combination where no matching PCI segment exists, causing the iterator variable to be used after the loop in an invalid state.
Ordinary below-host-admin reachability is not established by the supplied patch. In typical deployments, debugfs is host-global and writable debugfs controls are restricted to root or administrator-equivalent processes, but the exact permission bits are not included here. Therefore `HostAdminRequired=UNKNOWN`, not `YES`.
The operation is not namespace-scoped. There is no evidence that an attacker can create a user namespace or device namespace and obtain all required privileges for this AMD IOMMU debugfs operation.
No prior special hardware beyond AMD IOMMU support and the debugfs feature is treated as a scoring penalty. No network path exists. No race is involved.
4. Primitive and severity interpretation
The exact primitive is an invalid read / undefined behavior caused by using `pci_seg` after a failed list iteration, where it no longer denotes a valid `struct pci_segment`.
This is not an active structured UAF and not fixed stale storage. It is an invalid structured-object interpretation in a local debugfs control path. The demonstrated consequence is incorrect kernel behavior from reading `pci_seg->id` on a non-object pointer. A crash is possible in principle for undefined behavior, but not established as reliable by the patch.
Primitive class is `CLASS_C`: invalid-state / invalid-read behavior without an independently useful corruption primitive.
ImportantCandidate is `NO` because there is no UAF, no repeated lifetime/refcount mutation, no arbitrary write, no controlled reclaim, no security-boundary bypass, and no demonstrated LPE or protected-resource access.
AutoDowngradeAllowed is `YES` because the issue is low actionable risk and no unresolved Important-grade primitive remains.
Likely operational severity is Low / ordinary Moderate, mainly local robustness hardening for a debugfs path.
5. One-sentence report phrase
The AMD IOMMU debugfs devid_write handler could read pci_seg id after a failed PCI segment lookup, causing undefined behavior in a local debugfs write path without evidence of UAF, arbitrary write, information disclosure, or network reachability.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
Reason: this is a local debugfs invalid-read / undefined-behavior fix with no concrete kernel corruption primitive, no UAF, no authorization bypass, and no demonstrated remote or unprivileged exploit path.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: iommu/amd: Fix undefined behavior in devid_write debugfs function [ Upstream
Commit: 8aabe0fba01486b5d893e708b05a8fa7f1b7efbb
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8aabe0fba01486b5d893e708b05a8fa7f1b7efbb
Changed files:
drivers/iommu/amd/debugfs.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=8aabe0fba01486b5d893e708b05a8fa7f1b7efbb
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-92505 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-92505
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:N/I:N/A:L
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:L
The Best / paranoid CVSS score: 4.4
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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW
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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