[CVE-2026-53228][MODERATE 7.0] ipv6: sit: reload inner IPv6 header after GSO offloads [ Upstream

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

CVE: CVE-2026-53228
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ipv6: sit: reload inner IPv6 header after GSO offloads [ Upstream
Commit: fddd41445a0537b093e6b3f6232c9933cad1e48b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fddd41445a0537b093e6b3f6232c9933cad1e48b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53228
Analysis date: Thu, 25 Jun 2026 09:31:11 -0400
ActionableScore: 6
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum**:: Paranoid handling reaches Actionable Moderate because this is a real skb lifetime bug in a network tunnel transmit path. Conservative handling remains borderline because triggering depends on SIT tunnel configuration, GSO, cloned skb headers, and a specific offload path.
Manual review required: YES

Summary:
A stale inner IPv6 header pointer in the SIT tunnel transmit path can survive GSO offload handling and later read from freed skb header memory, causing at least DoS risk and limited worst-case confidentiality or integrity concern in configured tunnel deployments.

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

The original Linux kernel CVE announcement for CVE-2026-53228 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53228

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-53228	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';*CWE-416;CWE-825;CWE-362;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:H';BEST CVSS score: '6.4';DESCR 'An IPv6 SIT tunnel transmit path can keep a stale inner IPv6 header pointer across GSO offload handling. iptunnel_handle_offloads can unclone the skb header and pskb_expand_head can move the skb head, so later reads from iph6 may access freed skb header memory. The directly supported primitive is a UAF read of header fields such as hop limit and DS field, with likely impact ranging from kernel crash or warning to limited exposure or corruption of packet metadata. For the CVSS the PR:N reflects the paranoid network forwarding scenario where an attacker does not need local code execution if traffic can be routed into a configured SIT tunnel. The issue is not a generic Internet exposed service by default and usually depends on a configured SIT tunnel, GSO traffic, and skb header cloning conditions. Impact is at least denial of service and in the worst still defensible interpretation may include limited confidentiality or integrity impact from stale kernel memory reads.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	REMOTE READ DANGER UAF NETWORK SKB LINUS IPV6 SYZBOT KPANIC  KPANIC LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS 	NO	NO	checked

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

ActionableScore=6
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 6
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: Paranoid handling reaches Actionable Moderate because this is a real skb lifetime bug in a network tunnel transmit path. Conservative handling remains borderline because triggering depends on SIT tunnel configuration, GSO, cloned skb headers, and a specific offload path.

## 2. Signal breakdown

### Conservative score: 4

* Local unprivileged trigger: +1
  A local user may be able to generate traffic through an already configured SIT tunnel.
* Memory corruption, weak primitive: +1
  The patch describes a stale pointer into an skb header and a possible read from freed skb head memory, but only header fields are read and no write or reclaim primitive is shown.
* Real lifetime corruption: +1
  The issue is a stale pointer after `pskb_expand_head()` may move the skb head.
* Common networking packet-processing path: +1
  The bug is in IPv6 SIT tunnel transmit handling.
* Hard or configuration-dependent trigger: -1
  Requires GSO skb handling, cloned skb header state, and the path where `skb_realloc_headroom()` is not taken.
* Availability impact realistic: +1
  A UAF read in skb handling can plausibly lead to KASAN reports, warnings, or kernel crash depending on allocator state.

### Paranoid score: 6

* Network-triggerable / forwarding-path reachable: +2
  In a configured SIT tunnel or forwarding deployment, an attacker may influence packets entering the tunnel path without local code execution on the target.
* Memory corruption, weak primitive: +1
  The directly supported primitive is stale freed-memory read, not controlled overwrite.
* Real lifetime corruption: +1
  `skb_header_unclone()` and `pskb_expand_head()` can invalidate cached header pointers.
* Reliable kernel crash / strong DoS concern: +1
  syzbot reported the issue and the bug involves freed skb head access in kernel networking code.
* Confidentiality impact plausible: +1
  Limited stale-memory reads may affect header-derived behavior or expose small amounts of freed memory indirectly, but no direct disclosure API is shown.
* Integrity impact plausible: +1
  Stale reads of hop limit or DS field can corrupt packet metadata decisions in the worst defensible interpretation.
* Common networking packet-processing path: +1
  SIT is a packet transmit path in the kernel network stack.
* Hard or unreliable trigger: -1
  Requires specific skb clone and GSO/offload conditions.
* Rare/configuration-dependent exposure: -1
  SIT tunnels are not enabled by default on most general-purpose systems.

## 3. Reachability analysis

The conservative trigger is local traffic generation through an already configured SIT tunnel, so PR:L is the realistic baseline. Namespace or container delegation can matter if an untrusted workload can create or use tunnel devices through delegated network administration, but typical tunnel setup requires elevated privileges.

The paranoid trigger is network-adjacent or forwarding-path based. If the host is a SIT tunnel endpoint or router and external traffic can be routed into the affected transmit path, the attacker may not need local code execution on the target. This is not a generic Internet-exposed service by default. Realistic exploitation depends on SIT being configured, GSO/offload behavior being enabled, and skb header cloning conditions being reachable.

## 4. Severity interpretation

This is not an ordinary resource leak or validation-only bug. It is a real skb lifetime issue with a stale pointer into freed header memory. However, the demonstrated primitive is read-only and limited to IPv6 header fields, with no shown attacker-controlled reclaim, write-after-free, callback corruption, type confusion, or arbitrary write.

Conservatively it is borderline Moderate requiring manual review. Paranoid handling makes it Actionable Moderate because it combines a network packet path, real lifetime corruption, and possible network-adjacent triggering in tunnel deployments. It is not a strong Important by default without evidence of a stronger exploitation primitive.

## 5. One-sentence report phrase

A stale inner IPv6 header pointer in the SIT tunnel transmit path can survive GSO offload handling and later read from freed skb header memory, causing at least DoS risk and limited worst-case confidentiality or integrity concern in configured tunnel deployments.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This should not be auto-closed because it is a real UAF-style stale pointer read in skb networking code, and the practical exposure depends on tunnel configuration and forwarding reachability.

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

Patch: ipv6: sit: reload inner IPv6 header after GSO offloads [ Upstream
Commit: fddd41445a0537b093e6b3f6232c9933cad1e48b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fddd41445a0537b093e6b3f6232c9933cad1e48b

Changed files:
  net/ipv6/sit.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=fddd41445a0537b093e6b3f6232c9933cad1e48b

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

The original Linux kernel CVE announcement for CVE-2026-53228 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53228

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:L/I:N/A:H
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 6.4

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: 4
  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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).