[CVE-2026-53362][IMPORTANT] ipv6: account for fraggap on the paged allocation path [ Upstream

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

CVE: CVE-2026-53362
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: ipv6: account for fraggap on the paged allocation path [ Upstream
Commit: 14200d435af9a9eeb444f529fc2f689a236b7962
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=14200d435af9a9eeb444f529fc2f689a236b7962
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53362
Analysis date: Sat, 04 Jul 2026 08:51:43 -0400
ActionableScore: 10
ActionableScore lower bound: 8
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
An unprivileged local user can trigger an IPv6 __ip6_append_data() accounting bug with UDPv6 MSG_MORE and MSG_SPLICE_PAGES, causing an out-of-bounds write into skb_shared_info with kernel crash and plausible privilege escalation impact.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-53362 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53362

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: IMPORTANT
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-53362	IMPORTANT	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-131;CWE-122;BEST CVSS score: '7.8';DESCR 'An out of bounds write in the IPv6 __ip6_append_data paged allocation path can occur because fraggap is included in datalen but was not included in alloclen and was not subtracted from pagedlen. When MSG_MORE and MSG_SPLICE_PAGES drive the paged path on a UDPv6 socket, the carried fraggap bytes can be copied past the allocated skb linear area into skb_shared_info. For the CVSS the PR:L is selected because a local unprivileged process can trigger the vulnerable path with socket operations, while no remote packet alone is sufficient. The issue is not directly network reachable as an incoming network attack, but it can be reached by local code generating IPv6 UDP traffic. Impact is kernel memory corruption with likely denial of service and a plausible privilege escalation risk, so manual review is required.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 10)	YES	REMOTE DANGER NETWORK SKB IPV6 KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS	YES	NO	guess

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ACTIONABLESCORE ANALYSIS
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ActionableScore=10
ActionableScoreLower=8

## 1. ActionableScore

* Conservative score: 8
* Paranoid score: 10
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. The commit explicitly says an unprivileged user can trigger this through a UDPv6 socket with MSG_MORE and MSG_SPLICE_PAGES.
* Memory corruption, strong corruption primitive: +2. The patch fixes an out-of-bounds write past skb->end into trailing skb_shared_info.
* Memory layout invariant restoration: +1. The fix restores consistency between alloclen, pagedlen, datalen, fraggap, and copy in skb construction.
* Reliable kernel crash / strong DoS: +1. Writing into skb_shared_info is a credible kernel corruption and crash condition.
* Local unprivileged high-control kernel data-plane API: +1. The trigger uses socket plus splice/page based data movement to shape paged skb construction.
* Common networking core path or packet-processing path: +1. __ip6_append_data() is in the IPv6 output path and affects skb construction for UDPv6.
* Integrity impact plausible: +1. The write corrupts kernel skb metadata, not merely a bounds check failure.

Paranoid additional signals:

* Privilege escalation plausible: +2. The corrupted target is skb_shared_info, a high-value skb metadata area. The patch context supports a real OOB write primitive, and local privilege escalation is plausible even if not demonstrated.

No remote-reachable bonus is applied because this is not triggered by an incoming network packet alone.

## 3. Reachability analysis

A local unprivileged process can trigger the affected path by using UDPv6 sockets with MSG_MORE and MSG_SPLICE_PAGES under conditions that select the paged allocation branch. No CAP_NET_ADMIN or root privileges are indicated for the trigger. Containers and user namespaces may preserve reachability if the container can create IPv6 UDP sockets and use the relevant splice path, so treating this as PR:L is appropriate. The path is not directly remotely reachable, but it is in a common IPv6 networking subsystem and can be exercised by local code generating outbound UDPv6 traffic. Call-site confidence: high, because the affected function, arithmetic, trigger flags, and corruption target are all described in the provided patch context.

## 4. Severity interpretation

This behaves closer to an Important-class kernel vulnerability than an ordinary Moderate. The realistic baseline impact is local kernel memory corruption and likely DoS. The theoretical but technically defensible higher impact is local privilege escalation, because the bug writes past the skb linear allocation into skb_shared_info rather than only causing a NULL dereference, warning, or resource leak. There is no evidence for direct remote exploitation, so the score should not be treated as remote Critical, but it should not be auto-closed as a simple local DoS.

## 5. One-sentence report phrase

An unprivileged local user can trigger an IPv6 __ip6_append_data() accounting bug with UDPv6 MSG_MORE and MSG_SPLICE_PAGES, causing an out-of-bounds write into skb_shared_info with kernel crash and plausible privilege escalation impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This has a concrete OOB write into skb_shared_info from an unprivileged local trigger in a common networking path, so it needs manual security review even if no public exploit primitive is demonstrated.

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UPSTREAM PATCH SUMMARY
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Patch: ipv6: account for fraggap on the paged allocation path [ Upstream
Commit: 14200d435af9a9eeb444f529fc2f689a236b7962
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=14200d435af9a9eeb444f529fc2f689a236b7962

Changed files:
  net/ipv6/ip6_output.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=14200d435af9a9eeb444f529fc2f689a236b7962

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

The original Linux kernel CVE announcement for CVE-2026-53362 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53362

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:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

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: 8
  Paranoid ActionableScore: 10

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).