* [CVE-2026-98852][MODERATE REGULAR] net: extend IPv6 exthdr detection of tunneled packets [ Upstream
@ 2026-10-19 5:50 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-19 5:50 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98852
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net: extend IPv6 exthdr detection of tunneled packets [ Upstream
Commit: 44ba9dc568c878b699d05e7cf699572dc9df4b59
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=44ba9dc568c878b699d05e7cf699572dc9df4b59
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98852
Analysis date: Mon, 19 Oct 2026 01:50:43 -0400
ActionableScore: 3
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES
Summary:
Incorrect IPv6 extension header detection for tunneled GSO packets can cause unsafe inner header access and incorrect checksum fallback, resulting in warnings and packet loss, while remote or guest-to-host exploitation is not established.
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ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98852 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98852
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.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-98852 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98852 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE RESULT=DIFF (final Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-20;CWE-125;CWE-754;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.8';DESCR 'IPv6 extension header detection for tunneled GSO packets can inspect the wrong header or directly dereference an inner header that may not be safely accessible in the linear skb data. The confirmed effect is an incorrect checksum offload decision that can send a GSO skb to skb_checksum_help, produce a warning, and drop the packet. This can disrupt IPv6 tunnel traffic when extension headers, encapsulation, GSO, and checksum offload are used together. For the CVSS the PR:L reflects that reliable local triggering normally requires control of tunnel or virtual network configuration such as CAP_NET_ADMIN rather than full host administration. The issue is not proven to be reachable through ordinary remote packets because GSO and checksum metadata are internal skb state. An adjacent guest or virtual network trigger remains plausible when a backend accepts attacker influenced segmentation metadata, but this boundary is not established by the supplied patch. Impact is primarily denial of service or loss of network availability. The unsafe direct header read is an invalid read candidate, but there is no supported OOB write, UAF, information disclosure, or privilege escalation primitive. Automated impact decision path. The original SimpleNet classifier selected MODERATE. The primary LLM estimated paranoid CVSS 4.8 and the production ActionableScore returned 3 with recommendation Borderline / manual review recommended. 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. Exact triggered rule markers were V41_INHERITED_KPANIC_PROMOTION_BLOCKED and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 2.5 and ActionableScore 1 with primitive class CLASS_C and manual review RECOMMENDED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3) MAYBE REMOTE OOB SKB HARDWARE TEST IPV6 PACKET V41_INHERITED_KPANIC_PROMOTION_BLOCKED MANUAL_REVIEW_REQUIRED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=3
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw conservative score: 3
* Conservative score: 3
* Raw paranoid score: 3
* Paranoid score: 3
* No floor or cap was applied.
* Final recommended bucket: **Borderline / manual review recommended**::
2. Signal breakdown
Positive signals:
* +1 Common networking core packet-processing path. The affected helpers in `net/core/dev.c` participate in feature selection and checksum-offload handling, although the vulnerable combination is limited to tunneled IPv6 GSO traffic.
* +1 Weak invalid-read concern. Direct `inner_ip_hdr(skb)->version` access does not safely handle a non-linear, truncated, or otherwise inaccessible inner header. The replacement with `skb_header_pointer()` establishes a missing safe-access check, but no disclosure or write is shown.
* +1 Availability impact. Incorrect extension-header detection can direct a GSO packet to `skb_checksum_help()`, produce a warning, and drop the packet, disrupting affected tunnel traffic.
Non-awarded signals:
* No remote-reachability bonus. Ordinary network packets do not directly control internal GSO, header-offset, or checksum metadata.
* No local-unprivileged bonus. A complete below-host-admin trigger through virtio, TUN, a namespace, or another delegated interface is not established.
* No reliable-kernel-crash bonus. The demonstrated result is a warning and packet drop, not a host panic.
* No confidentiality or integrity bonus. The unsafe read is not copied to an attacker-visible destination and no kernel or packet-data overwrite is established.
* No V32 checksum-metadata corruption signal. The patch does not establish attacker-controlled `csum_start` or `csum_offset` causing a checksum write into a security-relevant header field.
* No V33 active-state candidate. No attacker-influenced write corrupting active structured state and no privileged downstream consumer of such corrupted state are identified.
* No B5-R retry-accumulated OOB write. There is no accumulating retry index, confirmed heap OOB write, or later consumption of corrupted descriptors.
* No B3-PENDING shared-backing write. The patch contains no demonstrated write to file-backed, shared, or COW storage.
* No authorization signal. There is no DENY-to-ALLOW decision or omitted capability check.
3. Reachability analysis
The confirmed path involves locally generated or forwarded tunneled IPv6 GSO packets combined with checksum-offload feature selection. Creating IPv6 tunnel devices generally involves network-administration control, but the supplied evidence does not prove that host-admin-equivalent privilege is required for the complete trigger. It also does not prove that every required operation works in an attacker-created user and network namespace.
The reference to virtio shows that encapsulated packets may exist without `skb->encapsulation`, but it does not establish that a malicious guest can independently control all relevant host-side SKB offsets, GSO type, checksum state, and tunnel processing. A guest or delegated TUN endpoint is therefore an unresolved possible boundary, not an established adjacent or guest-to-host attack path.
No special physical hardware is required, but suitable IPv6 tunneling, GSO, and checksum-offload behavior must be present. This is a deterministic state combination rather than a race.
4. Primitive and severity interpretation
The exact primitive is incorrect IPv6 extension-header classification plus a potentially unsafe direct read of an inner IPv6 header. The confirmed operational consequence is incorrect checksum fallback, a warning, and packet loss.
This is not a UAF, OOB write, lifetime violation, authorization bypass, or confirmed active-state corruption. The unsafe access can be treated as a limited invalid-read candidate, but the patch does not establish disclosure, useful control-flow influence, or a reliable host crash. The SKB remains an active packet object, but no attacker-influenced corruption of its structured state is demonstrated.
`PrimitiveClass=CLASS_C` is appropriate because the evidence supports invalid-state processing and availability degradation without an independently useful corruption primitive. `ImportantCandidate=NO` follows from the absence of a concrete cross-boundary write, protected-state modification, or strong crash primitive. `AutoDowngradeAllowed=YES` is appropriate, although manual review is still recommended to resolve virtio or delegated-interface reachability and the maximum consequence of the unsafe header read.
5. One-sentence report phrase
Incorrect IPv6 extension header detection for tunneled GSO packets can cause unsafe inner header access and incorrect checksum fallback, resulting in warnings and packet loss, while remote or guest-to-host exploitation is not established.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Confirm whether a guest-controlled virtio or delegated TUN path can supply the complete GSO and header-offset state, and determine whether the unsafe direct inner-header access can produce a host-wide fault rather than only packet loss.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: net: extend IPv6 exthdr detection of tunneled packets [ Upstream
Commit: 44ba9dc568c878b699d05e7cf699572dc9df4b59
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=44ba9dc568c878b699d05e7cf699572dc9df4b59
Changed files:
net/core/dev.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=44ba9dc568c878b699d05e7cf699572dc9df4b59
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98852 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98852
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:L/PR:L/UI:N/S:U/C:N/I:N/A:L
The Best / paranoid CVSS vector: AV:A/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 4.8
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: 3
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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