* [CVE-2026-98096][MODERATE 7.0] ipv6: sr: restore network header before routing and forwarding [ Upstream
@ 2026-09-25 14:11 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-25 14:11 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98096
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ipv6: sr: restore network header before routing and forwarding [ Upstream
Commit: ce4c8beedc19aceeab0e7bdc6f34394fb158c47c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ce4c8beedc19aceeab0e7bdc6f34394fb158c47c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98096
Analysis date: Fri, 25 Sep 2026 10:11:20 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98096 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98096
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-2026-98096 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98096 CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';CWE-195;*CWE-787;CWE-125;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '8.1';DESCR 'An IPv6 Segment Routing packet can leave skb_network_offset negative when another extension header such as Hop by Hop options appears before the SRH. During forwarding or redirection, downstream handlers can convert this negative offset to a large unsigned length and use it in memcpy or buffer processing, resulting in an OOB access or buffer overflow in the kernel. A remote attacker may trigger the issue by sending a crafted IPv6 SRH packet to a reachable SRv6 enabled forwarding node, although the required header layout and forwarding path make exploitation configuration dependent. For the CVSS the PR:N value is used because no account or local execution on the target is required once the vulnerable SRv6 packet processing path is network reachable. Impact is at least remote denial of service through a kernel crash. In the worst defensible case, the kernel buffer overflow may permit confidentiality and integrity impact or code execution, although a reliable arbitrary write primitive is not established and manual review is required.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6) SKIP CVE-2026-98096 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE REMOTE OOB BPF NETWORK SKB IPV6 KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHERTHAN5 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=6
ActionableScoreLower=5
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
1. ActionableScore
* Raw conservative score: 5
* Conservative score: 5
* Raw paranoid score: 6
* Paranoid score: 6
* No floor or cap was applied.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
Conservative signals:
* +1 Constrained kernel buffer overwrite. The commit directly establishes that a negative network offset can become an unsigned length and trigger OOB memcpy or buffer overflow. Exact destination, payload control, and overwrite extent are not visible.
* +2 Remote reachability. A crafted IPv6 packet can directly enter the vulnerable processing path on a network-reachable SRv6 forwarding endpoint without attacker credentials or local execution.
* +1 Reliable kernel crash or strong DoS. Passing a very large unsigned length into downstream copying or buffer processing can realistically fault or corrupt the kernel.
* +1 Common networking packet-processing path. The corrupted offset reaches IPv6 routing, forwarding, flow dissection, traffic-control redirection, fragmentation, or neighbour output.
* Total: 5.
Paranoid difference:
* +2 Strong corruption interpretation replaces the conservative +1 overwrite signal. The packet controls the extension-header arrangement that produces the negative offset, and the commit explicitly identifies OOB memcpy or buffer overflow rather than only an invalid read.
* The resulting paranoid total is 6.
* No separate Strong LPE bonus was awarded because controlled destination selection, controlled overwrite contents, callback influence, or arbitrary kernel write is not established.
* No additional Availability point was awarded because it would duplicate the same crash consequence.
* Confidentiality was not awarded because no disclosure path is shown.
* Integrity was not separately awarded because the known buffer overflow is already represented by the corruption primitive and its security-useful target is unresolved.
* Controlled reclaim, UAF, type confusion, privilege escalation, and code execution are not demonstrated.
* No race or timing penalty applies.
* No rarity penalty was applied. SRv6 forwarding requires prior configuration, but the supplied evidence does not establish that deployed SRv6 endpoints are both rare and difficult for network attackers to reach.
3. Reachability analysis
The evaluated attacker is a remote unauthenticated network peer capable of sending a crafted IPv6 packet containing an extension header before an SRH with `segments_left` greater than zero. The vulnerable node must already have the applicable SRv6 processing and forwarding or redirection path configured.
That configuration is prior administrative deployment setup, but the attacker does not need host-admin privilege to send the triggering packet once the endpoint is exposed. Therefore, `HostAdminRequired=NO`. No namespace capability is part of the remote trigger, so `NamespaceScopedPrivilege=NO`.
The strongest consequence requires the packet to continue through `ip6_forward`, `act_mirred`, `sch_fragment`, neighbour output, or another handler that interprets the negative offset as an unsigned length. No special hardware, local process, attacker-controlled namespace, or timing race is required.
4. Primitive and severity interpretation
The exact primitive is a signed-to-unsigned length conversion caused by an incorrectly restored SKB data position. The resulting large length reaches downstream memory-copy or buffer-processing operations and can cause an OOB access or buffer overflow.
This is not a UAF, stale-object issue, cleanup-only failure, or repeated refcount mutation. It is active packet-processing corruption involving an attacker-influenced SKB.
The conservative interpretation is a constrained kernel overwrite because the supplied diff does not expose the destination buffer, copy direction, payload source, or overwrite extent. The paranoid interpretation treats it as a stronger attacker-influenced OOB write because crafted packet layout determines the invalid offset and the commit explicitly confirms buffer-overflow sinks.
`PrimitiveClass=CLASS_B` is selected because real kernel memory corruption is established, but a directed or security-useful overwrite sufficient for Class A is not. The demonstrated consequence is remote kernel crash or corruption. Code execution and privilege escalation remain technically possible concerns, not established consequences.
`ImportantCandidate=YES` and `ManualReview=REQUIRED` follow from the network-reachable kernel buffer overflow and unresolved downstream overwrite properties. `AutoDowngradeAllowed=NO` because automatically treating it as ordinary DoS could discard a meaningful corruption primitive whose destination and attacker control require source-level review.
5. One-sentence report phrase
A crafted IPv6 SRH packet can preserve a negative SKB network offset that downstream forwarding handlers reinterpret as a large unsigned copy length, causing a remotely triggerable kernel OOB access or buffer overflow on configured SRv6 nodes.
6. Manual review recommendation
MANUAL CHECK REQUIRED
Review the downstream `sch_fragment`, neighbour-output, and `act_mirred` call paths to determine the copy direction, destination allocation, attacker control over copied bytes and length, and whether the overflow can modify active kernel objects rather than only causing an immediate fault.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: ipv6: sr: restore network header before routing and forwarding [ Upstream
Commit: ce4c8beedc19aceeab0e7bdc6f34394fb158c47c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ce4c8beedc19aceeab0e7bdc6f34394fb158c47c
Changed files:
net/ipv6/exthdrs.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=ce4c8beedc19aceeab0e7bdc6f34394fb158c47c
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98096 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98096
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:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
The Best / paranoid CVSS score: 8.1
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: 5
Paranoid ActionableScore: 6
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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