* [CVE-2026-98080][MODERATE 7.0] btrfs: do not force reloc root creation during qgroup_account_snapshot() [ Upstream
@ 2026-10-05 14:09 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-10-05 14:09 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98080
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: btrfs: do not force reloc root creation during qgroup_account_snapshot() [ Upstream
Commit: c4c78768d1a8ceb713693cc5524acbe984c31f3c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c4c78768d1a8ceb713693cc5524acbe984c31f3c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98080
Analysis date: Mon, 05 Oct 2026 10:09:50 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98080 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98080
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-2026-98080 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98080 CHECK WITH IMPACT FROM ORIG NN NONE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:H/A:H';*CWE-672;*CWE-664;CWE-682;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:H/A:H';BEST CVSS score: '6.5';DESCR 'A Btrfs transaction ordering flaw can create a relocation root too late during qgroup snapshot accounting. The relocation root may then reference a metadata extent that has already been dropped after the commit root and current root diverged. This produces inconsistent extent references, can corrupt the extent tree, and can force the filesystem into read only mode. The demonstrated impact is persistent filesystem integrity damage and loss of availability rather than a simple warning or transient process failure. For the CVSS the PR:L value in the paranoid score reflects environments where a restricted local user can create snapshots while an administrator controlled relocation or balance operation is active. Reliable direct control of all required conditions normally requires PR:H, so PR:L represents the highest still defensible multi tenant interpretation. The issue is not network reachable. AC:H applies because exploitation depends on a specific timing and state combination involving enabled qgroups, relocation initialization, transaction commit, and snapshot accounting. Impact is at least local denial of service and filesystem integrity corruption. A limited confidentiality impact is conservatively retained because damaged extent references may require manual analysis to exclude unintended data association, although no direct information disclosure or kernel memory write primitive is demonstrated.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate (with actual score 5) MAYBE DANGER DISK INIT SKIP HARDWARE KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
1. ActionableScore
* Raw conservative score: 4
* Conservative score: 4
* Raw paranoid score: 5
* Paranoid score: 5
* No floor or cap was applied.
* Final recommended bucket: **Actionable Moderate**::
2. Signal breakdown
Conservative signals:
* +1 Weak or indirect corruption candidate. A relocation root receives a reference to a metadata extent that has already been released from the filesystem tree.
* +1 Integrity impact. The stale reference produces inconsistent extent references and confirmed extent-tree corruption.
* +1 Reliable strong DoS. The error forces the affected Btrfs filesystem into read-only mode.
* +1 Important filesystem path. The defect affects Btrfs COW, relocation, delayed references, and extent ownership metadata.
Paranoid-only signal:
* +1 Active-state lifetime and consistency violation. The reloc root is created from an obsolete commit-root view after the referenced tree block was COWed away, and the stale association is subsequently consumed by delayed-reference processing. This is stronger than passive bookkeeping corruption but does not establish a kernel-memory UAF.
Not awarded:
* Real UAF was not awarded. The released object is a filesystem metadata extent, not a demonstrated freed kernel-memory object subsequently dereferenced.
* Local unprivileged trigger was not awarded. A restricted user may be able to initiate snapshot activity, but the demonstrated sequence also includes Btrfs relocation or balance and the complete privilege boundary is unresolved.
* Strong LPE leverage was not awarded. No controlled reclaim, arbitrary write, callback influence, credential modification, or cross-file ownership violation is established.
* Confidentiality was not awarded. No stale-block disclosure or unauthorized read-back path is shown.
* Dirty-Pipe-like ownership or COW bypass was not awarded. The patch shows corruption of Btrfs own metadata, not an authorized write to one object modifying an independently permissioned object.
* Extra Availability was not awarded. The read-only transition is already represented by the strong DoS point.
* No race penalty was applied. The defect depends on transaction ordering and filesystem state, but the evidence does not establish a narrow or externally uncontrollable race.
* No host-admin penalty was applied. The demonstrated balance path is privileged, but it is unresolved whether a less-privileged snapshot creator can supply the triggering operation while an administrator-controlled relocation is already active.
Repeated-release checks:
* No repeated release or refcount operation on the same kernel reference is established.
* No concrete repeated-release point was awarded.
* No paranoid repeated-refcount point was awarded.
* REAL UAF FLOOR 5 was not applied.
3. Reachability analysis
The demonstrated reproducer uses quota-enabled Btrfs, snapshot accounting, transaction commit, and block-group relocation or balance. The visible balance ioctl path is normally administrator-controlled, but snapshot creation may be performed by a different actor depending on mount permissions and deployment policy.
The complete below-host-admin trigger is not established, so HostAdminRequired is UNKNOWN rather than NO. It is also inappropriate to assume that the attacker must personally control every administrative stage when relocation could already be running as a legitimate maintenance operation.
No evidence establishes that the complete sequence is available through attacker-created user or mount namespaces. NamespaceScopedPrivilege is therefore UNKNOWN. No special physical hardware is required. Quotas and relocation are configuration prerequisites, but Btrfs itself is an important production storage subsystem.
The issue is not remotely reachable. It is a local filesystem-control and transaction-ordering problem rather than a packet-triggered path.
4. Primitive and severity interpretation
The exact primitive is creation of an active relocation-tree reference to a metadata extent that has already been removed after the current root and commit root diverged. Later delayed-reference processing treats that obsolete association as valid and corrupts the extent tree.
This is a stale filesystem ownership and lifetime association, not a kernel heap UAF. It is classified as CLASS_B because an obsolete reference escapes into active metadata processing and causes persistent structural corruption. It is not CLASS_A because there is no attacker-directed write, cross-owner COW violation, controlled replacement, or demonstrated privilege-escalation primitive.
The demonstrated consequences are extent-tree corruption and a forced read-only filesystem. Broader data association or privilege-escalation consequences remain speculative. ImportantCandidate is NO because the evidence does not establish Important-grade exploitation leverage. ManualReview is REQUIRED and AutoDowngradeAllowed is NO because automatically treating the issue as a warning-only or ordinary DoS defect would discard the confirmed persistent metadata-integrity impact and the unresolved multi-actor reachability question.
Likely operational severity is Actionable Moderate. An Important rating would require evidence of unprivileged reliable triggering, cross-object ownership corruption, unauthorized data exposure, or another stronger primitive.
5. One-sentence report phrase
A Btrfs transaction-ordering flaw can create a relocation root that references an already released metadata extent, causing persistent extent-tree corruption and forcing the filesystem into read-only mode.
6. Manual review recommendation
MANUAL CHECK REQUIRED
The issue has confirmed persistent filesystem metadata corruption, while the ability of a restricted snapshot creator to trigger it during an administrator-controlled relocation remains unresolved.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: btrfs: do not force reloc root creation during qgroup_account_snapshot() [ Upstream
Commit: c4c78768d1a8ceb713693cc5524acbe984c31f3c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c4c78768d1a8ceb713693cc5524acbe984c31f3c
Changed files:
fs/btrfs/extent-tree.c
fs/btrfs/transaction.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=c4c78768d1a8ceb713693cc5524acbe984c31f3c
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98080 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98080
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:H/A:H
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:H/A:H
The Best / paranoid CVSS score: 6.5
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: 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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