* [CVE-2026-80736][MODERATE REGULAR] thunderbolt: Fix bandwidth group reservation indexing
@ 2026-09-03 9:10 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-03 9:10 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-80736
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: thunderbolt: Fix bandwidth group reservation indexing
Commit: 0bfb67ba366cd68d1d0ad935760577bae1d5df27
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0bfb67ba366cd68d1d0ad935760577bae1d5df27
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80736
Analysis date: Thu, 03 Sep 2026 05:10:01 -0400
ActionableScore: 4
ActionableScore lower bound: 2
Actionable bucket: Borderline manual review recommended. Not a Strong Important candidate by default
Manual review required: YES
Summary:
A Thunderbolt DisplayPort bandwidth accounting bug can access one element past a stack array when Group ID equals MAX_GROUPS, requiring physical or firmware-mediated Thunderbolt or USB4 conditions and mainly raising constrained kernel memory corruption and DoS concerns.
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ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-80736 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80736
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.
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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-80736 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-80736 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-125;CWE-193;Other CVSS 'AV:P/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '6.4';DESCR 'An off by one out of bounds access can occur in the Thunderbolt DisplayPort bandwidth accounting path because valid bandwidth group IDs are 1 through MAX_GROUPS while group_reserved was allocated with only MAX_GROUPS entries. When group ID MAX_GROUPS is used as a direct array index, tb_consumed_dp_bandwidth can access one element past the local array and may corrupt adjacent stack state or compute reserved bandwidth incorrectly. For the CVSS the PR:N is used because a physical attacker with a crafted or specific Thunderbolt setup does not need a local account on the target system. The issue is not network reachable and normally requires physical access to Thunderbolt or USB4 DisplayPort tunneling hardware. Impact is at least denial of service or incorrect bandwidth reservation, and because the primitive is a kernel out of bounds stack access, limited confidentiality or integrity impact cannot be ruled out without manual review.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended. Not a Strong Important candidate by default (with actual score 3) YES SIMPLEFIX INCREASED_TO_MODERATE7_FROM_MODERATE_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 YES NO checked
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ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=4
ActionableScoreLower=2
## 1. ActionableScore
* Conservative score: 2
* Paranoid score: 4
* Final recommended bucket: **Borderline manual review recommended. Not a Strong Important candidate by default**::
## 2. Signal breakdown
Conservative signals:
* Firmware-mediated external influence: +1
Thunderbolt or USB4 topology and DisplayPort bandwidth group state can be influenced by attached hardware, firmware, docks, or display tunneling behavior, but this is not remotely network reachable.
* Constrained kernel buffer overwrite / weak OOB corruption candidate: +1
`group_reserved[MAX_GROUPS]` is a one-element out-of-bounds stack array access when Group ID equals `MAX_GROUPS`. The affected value appears to be bandwidth accounting metadata, not an attacker-chosen arbitrary payload.
* Physical-only or rare hardware-only condition: -2
Practical triggering normally requires physical Thunderbolt or USB4 DisplayPort tunneling hardware and a specific group ID state.
* Effective conservative result: 2
This is above ordinary correctness because it is an OOB stack access in kernel code, but the trigger and control appear highly constrained.
Paranoid additional signals:
* Privileged kernel/device-management memory corruption path: +1
The corruption occurs inside Thunderbolt bandwidth management, a trusted kernel device-management path.
* Integrity/availability concern from corrupted stack accounting state: +1
The final group reservation is not accounted correctly, and adjacent stack state could theoretically be affected. This remains constrained and hardware-dependent.
* Effective paranoid result: 4
Manual review is justified, but there is not enough evidence for Actionable Moderate or Important classification.
## 3. Reachability analysis
A realistic attacker would need influence over Thunderbolt or USB4 DisplayPort tunneling state, most plausibly through a physically attached device, dock, display chain, or firmware-mediated topology behavior. No network reachability is indicated. No local Linux account is necessarily required for a physical attacker, so PR:N is defensible in CVSS terms, but the ActionableScore is reduced because the condition is physical and hardware-specific.
Namespaces and containers do not materially help trigger this issue because the relevant path is hardware and kernel device-management driven, not a normal namespaced syscall or netlink data-plane API. The affected subsystem is common on some laptops and workstations, but the exact DisplayPort bandwidth group condition is narrow.
## 4. Severity interpretation
This behaves like a constrained physical or firmware-mediated kernel OOB access rather than a typical local privilege escalation bug. Theoretical memory corruption exists because the array is on the stack and Group ID `MAX_GROUPS` indexes one element past the end. Realistic exploitation evidence is weak because the overwritten or read value appears to be kernel-derived bandwidth accounting data, the target is not attacker-selected, and no reclaim, callback, type confusion, arbitrary write, or information leak primitive is shown.
Overall this should not be auto-dismissed as pure bookkeeping, but it is also not a Strong Important candidate based on the supplied patch alone.
## 5. One-sentence report phrase
A Thunderbolt DisplayPort bandwidth accounting bug can access one element past a stack array when Group ID equals MAX_GROUPS, requiring physical or firmware-mediated Thunderbolt or USB4 conditions and mainly raising constrained kernel memory corruption and DoS concerns.
## 6. Manual review recommendation
MANUAL CHECK REQUIRED
Reason: the patch fixes a concrete one-element out-of-bounds stack access in kernel code. The practical exploitability is likely low and physical-only, but memory corruption is present, so manual review is appropriate before autoclosing.
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: thunderbolt: Fix bandwidth group reservation indexing
Commit: 0bfb67ba366cd68d1d0ad935760577bae1d5df27
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0bfb67ba366cd68d1d0ad935760577bae1d5df27
Commit description:
Valid bandwidth group IDs range from 1 through MAX_GROUPS, while Group
ID 0 is reserved. tb_consumed_dp_bandwidth() uses the Group ID directly
to index its local group_reserved[] array.
The array currently has MAX_GROUPS entries, so its valid indices are 0
through MAX_GROUPS - 1. Group ID MAX_GROUPS therefore accesses one
element past the end, and the final group's reserved bandwidth is not
included when the array is summed.
Give group_reserved[] MAX_GROUPS + 1 entries so direct Group ID
indexing covers the reserved ID 0 and valid IDs 1 through MAX_GROUPS.
Fixes: 52a4490 ("thunderbolt: Reserve released DisplayPort bandwidth for a group for 10 seconds")
Cc: [email protected]
Signed-off-by: Xu Rao <[email protected]>
Signed-off-by: Mika Westerberg <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
drivers/thunderbolt/tb.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=0bfb67ba366cd68d1d0ad935760577bae1d5df27
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-80736 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80736
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:P/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
The Best / paranoid CVSS vector: AV:P/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
The Best / paranoid CVSS score: 6.4
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: 2
Paranoid ActionableScore: 4
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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