* [CVE-2026-98625][MODERATE 7.0] netfilter: flowtable: publish HW_DEAD after worker is done [ Upstream
@ 2026-10-24 10:00 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-24 10:00 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98625
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: netfilter: flowtable: publish HW_DEAD after worker is done [ Upstream
Commit: f92e8f39726ba68a7c42c6b7566be687c8161579
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f92e8f39726ba68a7c42c6b7566be687c8161579
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98625
Analysis date: Sat, 24 Oct 2026 06:00:56 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
A race allows an RCU-freed flow object to receive a later atomic bit write from its destroy worker, creating a concrete but constrained post-free corruption primitive.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98625 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98625
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-2026-98625 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98625 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 LEGACY=MODERATE_KPANIC RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.5';DESCR 'A race in netfilter flowtable hardware offload can free a flow while its destroy worker is still using it. The worker holds neither an RCU read lock nor a flow reference, so garbage collection can schedule and complete RCU freeing after HW_DEAD is published but before the worker clears HW_PENDING. The later atomic bit clear becomes a constrained write to freed and potentially reallocated slab memory, making kernel crash the direct impact and broader memory corruption a plausible worst case. For the CVSS the PR:N value is used because an attacker may drive ordinary traffic through an already configured hardware flowtable without holding local privileges, although configuration of the vulnerable offload path still requires an administrator. Attack complexity is high because exploitation depends on worker preemption, concurrent garbage collection, RCU timing, and useful slab reuse. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 7.5 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE_KPANIC to IMPORTANT because the CVSS score, vector or bug class threshold rule was applied. KP and FD specialist checks stage IMPORTANT to MODERATE_KPANIC because KP specialist did not establish a qualifying panic. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were INCREASED_TO_HIGH_BASED_ON_GUESSCVSS and DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP. The independent weaker Aegis shadow evaluated CVSS 2.5 and ActionableScore 4 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE REMOTE NETFILTER UAF LINUS KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 2.
* Conservative score: 5. Manual-review safety floor raises 2 -> 5 for a concrete post-free atomic write with unresolved exploit leverage.
* Raw paranoid score: 3.
* Paranoid score: 5. The same safety floor raises 3 -> 5.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
* +2: Real UAF. `HW_DEAD` permits GC and RCU freeing while the unreferenced worker still holds `offload->flow`.
* +1: Reliable kernel crash/strong DoS is plausible when the worker resumes and accesses freed slab storage.
* -1: The race is specifically timing-sensitive: worker preemption, concurrent GC, RCU completion, and resumption must align.
* Paranoid +1: `clear_bit(NF_FLOW_HW_PENDING, ...)` is an actual write-like atomic mutation at a potentially reallocated slab address, not merely a stale read.
* No remote-reachability bonus: ordinary traffic through an already configured flowtable is plausible, but the supplied patch does not establish the complete packet-to-destroy/GC trigger chain.
* No Class A leverage: controlled reclaim, selected replacement object, arbitrary target/payload, callback control, disclosure, and LPE are not shown.
* No extra availability point: it would duplicate the same crash.
* NEW52/B5-R does not apply: there is no retry-accumulated index or heap OOB sequence.
* B4 does not apply: no authorization decision changes from DENY to ALLOW.
3. Reachability analysis
The supplied summary grounds a plausible adjacent traffic actor after an administrator configures hardware flowtable offload. Prior privileged setup therefore appears necessary, but the patch does not resolve whether traffic alone can reliably initiate flow destruction and the required GC sequence. Consequently, effective host-admin and namespace privilege requirements remain unknown. No special hardware rarity penalty is applied, and the demonstrated race difficulty is already counted once.
4. Primitive and severity reading
This is an active flow-object lifetime violation, not fixed stale storage. Publishing `HW_DEAD` before the worker's final access allows RCU freeing; the later `clear_bit()` then performs a constrained write through the dangling pointer. That is CLASS_B post-lifetime corruption. A later consumer of any reallocated/corrupted object is not shown, so arbitrary corruption or integrity impact is speculative. ImportantCandidate is YES because a concrete post-free write remains with materially unresolved leverage; AutoDowngradeAllowed is NO for the same reason.
5. One-sentence report phrase
A race allows an RCU-freed flow object to receive a later atomic bit write from its destroy worker, creating a concrete but constrained post-free corruption primitive.
6. Manual review advice
MANUAL CHECK REQUIRED
Confirm packet-only reachability, slab reuse behavior, and whether the cleared bit can corrupt subsequently allocated active state.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: netfilter: flowtable: publish HW_DEAD after worker is done [ Upstream
Commit: f92e8f39726ba68a7c42c6b7566be687c8161579
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f92e8f39726ba68a7c42c6b7566be687c8161579
Changed files:
net/netfilter/nf_flow_table_offload.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=f92e8f39726ba68a7c42c6b7566be687c8161579
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98625 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98625
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:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
The Best / paranoid CVSS score: 7.5
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: unknown
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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