[CVE-2026-98802][MODERATE 7.0] seg6: ensure packet data is writable before modifying SRH and IPv6 DA [ Upstream

[CVE-2026-98802][MODERATE 7.0] seg6: ensure packet data is writable before modifying SRH and IPv6 DA [ Upstream

[AL-KERNEL]

CVE: CVE-2026-98802
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: seg6: ensure packet data is writable before modifying SRH and IPv6 DA [ Upstream
Commit: e9141fdb7a2ead48cfcd60c681aba91d3014255b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e9141fdb7a2ead48cfcd60c681aba91d3014255b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98802
Analysis date: Sat, 24 Oct 2026 11:39:10 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
A remote SRv6 packet can cause seg6local to modify shared skb header bytes, allowing an AF_PACKET clone consumer to observe altered rather than original ingress metadata.

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

The original Linux kernel CVE announcement for CVE-2026-98802 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98802

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-2026-98802	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98802 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 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:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N';CWE-362;*CWE-664;BEST CVSS score: '5.3';DESCR 'IPv6 SRv6 seg6local processing could modify the SRH Segments Left field and IPv6 destination address while the skb data remained shared with a clone queued to an AF_PACKET socket. A remote sender can supply the packet when a reachable SRv6 local SID and affected End behavior are configured. The concrete impact is low integrity loss because a packet capture or another clone consumer can observe modified metadata instead of the original ingress packet. There is no evidence of an out of bounds access, use after free, arbitrary write, information disclosure, or kernel crash. For the CVSS the PR:N value is selected because the sender needs only packet reachability and does not need a local account or privileges on the target. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 5.3 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. No severity changing production threshold or specialist override was recorded. 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. The independent weaker Aegis shadow evaluated CVSS 3.7 and ActionableScore 2 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 READ OOB DANGER NOMEMCHK NETWORK SKB HARDWARE LINUS IPV6 KPANIC PACKET 	-	-	checked

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

ActionableScore=5
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 5.
* Conservative score: 5; no floor or cap applied.
* Raw paranoid score: 5.
* Paranoid score: 5; no additional speculative impact scored.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

* +2 remote reachability: supplied call-path evidence supports a remote sender reaching an already configured SRv6 local SID without trigger-time local privilege.
* +1 constrained shared-state write: `segments_left` and the IPv6 destination address are modified while packet storage remains shared with an AF_PACKET clone.
* +1 integrity impact: the clone consumer can receive packet metadata different from the original ingress packet.
* +1 practical chain: remote packet → AF_PACKET clone → seg6local modification of shared bytes → packet socket reads modified clone.
* No OOB, UAF, arbitrary target, kernel-memory overwrite, crash, disclosure, or LPE is shown.
* No extra common-network-path point: the affected seg6local behavior requires prior SRv6 configuration.
* B5-R does not apply: there is no retry-accumulated heap OOB write.
* B3-PENDING does not apply: shared skb storage is proven, but file/page-cache/shared-backing storage is not.
* No authorization signal applies.

3. Reachability analysis

The triggering actor can be a remote sender after an administrator has configured a reachable SRv6 local SID and affected End behavior. That prior setup does not make each later packet trigger host-admin-only, so `HostAdminRequired=NO`. AF_PACKET creation normally requires CAP_NET_RAW, but that privilege belongs to the affected clone consumer, not the remote sender. Namespace scope and whether the consumer is a host capture service or delegated namespace endpoint are unresolved. No race, unusual hardware, or retry sequence is required.

4. Primitive and severity reading

The exact primitive is a bounded in-skb write through shared packet storage without first obtaining private writable data. The changed active fields are SRH Segments Left and IPv6 destination address; the demonstrated later consumer is the queued AF_PACKET clone.

This is CLASS_B shared-state/ownership corruption, not kernel-memory OOB corruption. The shown effect is packet-observation integrity loss. A protected-file overwrite, routing-policy bypass, namespace escape, or host compromise is not shown.

ImportantCandidate is retained because attacker-influenced active packet state is consumed across a remote-to-local privileged/delegated packet-interface boundary whose broader consumers remain unresolved. Auto-downgrade is therefore disallowed pending review, without asserting Important severity as proven.

5. One-sentence report phrase

A remote SRv6 packet can cause seg6local to modify shared skb header bytes, allowing an AF_PACKET clone consumer to observe altered rather than original ingress metadata.

6. Manual review advice

MANUAL CHECK REQUIRED

Review downstream clone consumers and namespace/delegated AF_PACKET boundaries; only bounded packet-integrity impact is currently proven.

7. Call-site confidence

Call-site confidence: high

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

Patch: seg6: ensure packet data is writable before modifying SRH and IPv6 DA [ Upstream
Commit: e9141fdb7a2ead48cfcd60c681aba91d3014255b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e9141fdb7a2ead48cfcd60c681aba91d3014255b

Changed files:
  net/ipv6/seg6_local.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=e9141fdb7a2ead48cfcd60c681aba91d3014255b

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

The original Linux kernel CVE announcement for CVE-2026-98802 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98802

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: Not available
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
  The Best / paranoid CVSS score: 5.3

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