[CVE-2026-98934][LOW] ipv6: sr: use skb_get_hash_net() in seg6_make_flowlabel() [ Upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-98934
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: ipv6: sr: use skb_get_hash_net() in seg6_make_flowlabel() [ Upstream
Commit: 4ab37e4f4a33c64d9e565dc8c4c3ed774f05c0e3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4ab37e4f4a33c64d9e565dc8c4c3ed774f05c0e3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98934
Analysis date: Mon, 26 Oct 2026 15:43:21 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
A delegated network administrator can trigger a flow-dissector warning through a specially configured TIPC/seg6 path, with a conditional crash only under panic-on-warning policy.

======================================================================
ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-98934 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98934

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-2026-98934	LOW	https://www.kernelcve.org/list/?q=CVE-2026-98934 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT LOW AEGIS_AS=0 LEGACY=LOW RESULT=SAME (final reconciliation agrees; DECISION: both 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:N/I:N/A:H';*CWE-20;**CWE-476;CWE-754;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'seg6_make_flowlabel could call the flow dissector lacking a network namespace when an internally generated skb has neither skb dev nor skb sk. The demonstrated path requires a TIPC UDP bearer, an IPv4 route using seg6 encapsulation, and net ipv6 seg6_flowlabel set to 1. The direct effect is a kernel warning and failure to obtain the intended packet hash, with no evidence of UAF, OOB access, information disclosure, or an arbitrary write. Availability impact is normally limited, although systems configured with panic_on_warn may turn the warning into a kernel crash. For the CVSS the PR:L value reflects that reliable triggering requires a local actor able to configure the TIPC bearer and Segment Routing route through delegated network administration privileges. Ordinary remote packet reachability alone does not establish a trigger. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 4.7 and the production ActionableScore returned 0 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. No severity changing production threshold or specialist override was recorded. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. The independent weaker Aegis shadow evaluated CVSS 0.0 and ActionableScore 0 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was LOW. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0)	MAYBE	REMOTE BPF NETWORK SKB HARDWARE IPV6 SYZBOT 	-	-	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=0
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 0.
* Conservative score: 0; no floor or cap applied.
* Raw paranoid score: 0 (+1 conditional kernel crash under `panic_on_warn`, -1 positively evidenced delegated network-administration privilege).
* Paranoid score: 0; no floor or cap applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* Paranoid +1: the demonstrated `WARN` can become a host crash where `panic_on_warn` is enabled.
* Paranoid -1: reliable triggering requires delegated network-management authority to configure the TIPC bearer, Segment Routing route, and flow-label setting.
* No UAF, OOB access, write, stale lifetime, shared-backing modification, or corrupted structured-state consumption is shown.
* No extra availability point: the conditional panic is the same warning event.
* No remote-reachability point: ordinary network traffic cannot establish the required control-plane configuration.
* No authorization bypass: the patch supplies the missing network-namespace context to flow dissection; it does not restore an access-control decision.
* NEW52/B5-R and NEW53/B3-PENDING do not apply.

3. Reachability analysis

The grounded trigger is a local, delegated network administrator configuring a TIPC UDP bearer, IPv4 route with seg6 encapsulation, and `net.ipv6.seg6_flowlabel=1`. The supplied evidence supports below-host-admin delegated access, hence `HostAdminRequired=NO` and `RequiresHostUID0=NO`. It does not establish that every required operation is available in attacker-created user/net namespaces, so namespace-scoped privilege remains unknown. No race, special hardware, or remote packet-only trigger is shown.

4. Primitive and severity reading

The defect passes no usable `struct net` source to `__skb_flow_dissect()` when both `skb->dev` and `skb->sk` are absent. The shown result is a warning and failed hash acquisition, classified as CLASS_C invalid-state/DoS behavior. There is no active-state corruption, downstream privileged consumer, or trust-boundary corruption chain. Stronger effects are limited to a configuration-dependent panic; no non-crash exploitation leverage is evidenced. Auto-downgrade is therefore allowed.

5. One-sentence report phrase

A delegated network administrator can trigger a flow-dissector warning through a specially configured TIPC/seg6 path, with a conditional crash only under panic-on-warning policy.

6. Manual review advice

NO MANUAL CHECK NEEDED

No memory-corruption, authorization, ownership, or cross-boundary primitive remains unresolved.

7. Call-site confidence

Call-site confidence: high

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: ipv6: sr: use skb_get_hash_net() in seg6_make_flowlabel() [ Upstream
Commit: 4ab37e4f4a33c64d9e565dc8c4c3ed774f05c0e3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4ab37e4f4a33c64d9e565dc8c4c3ed774f05c0e3

Changed files:
  net/core/flow_dissector.c
  include/linux/skbuff.h
  net/ipv6/seg6_iptunnel.c
  net/core/lwtunnel.c
  include/net/dst.h
  net/ipv4/ip_output.c
  net/ipv4/ip_tunnel_core.c
  net/ipv4/udp_tunnel_core.c
  net/tipc/udp_media.c
  net/tipc/bearer.c
  net/netlink/genetlink.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=4ab37e4f4a33c64d9e565dc8c4c3ed774f05c0e3

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-98934 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98934

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:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: unknown
  Paranoid ActionableScore: 0

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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).