[CVE-2026-68420][MODERATE 7.0] xfrm: reject optional IPTFS templates in outbound policies [ Upstream

[CVE-2026-68420][MODERATE 7.0] xfrm: reject optional IPTFS templates in outbound policies [ Upstream

[AL-KERNEL]

CVE: CVE-2026-68420
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: xfrm: reject optional IPTFS templates in outbound policies [ Upstream
Commit: d7fc6f351c478586980a521d63b0214d9c055e78
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d7fc6f351c478586980a521d63b0214d9c055e78
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68420
Analysis date: Mon, 10 Aug 2026 20:30:06 -0400
ActionableScore: 5
ActionableScore lower bound: 2
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
An optional IPTFS template in an outbound XFRM policy can drive the outbound resolution path into a stack out-of-bounds read in `xfrm_state_find()`, causing at least local DoS and requiring manual review because namespace-delegated CAP_NET_ADMIN may reduce the practical privilege barrier.

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

The original Linux kernel CVE announcement for CVE-2026-68420 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68420

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-2026-68420	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H';CWE-125;*CWE-20;*CWE-787;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.1';DESCR 'An outbound XFRM policy can accept an optional IPTFS template even though IPTFS should follow the same restriction as tunnel mode. This invalid policy state can drive xfrm_tmpl_resolve_one into xfrm_state_find and trigger a stack out of bounds read in __xfrm6_addr_hash when outbound traffic is resolved. For the CVSS the PR:L is used for the paranoid score because reliable triggering requires local ability to install XFRM policies, but this capability may be delegated to container root, reduced capability root, or a network management service account rather than full host root. The issue is not directly network reachable because packets alone do not create the malformed policy. Impact is at least local denial of service via KASAN warning or kernel crash. In the worst still defensible case, the concrete out of bounds read may justify limited confidentiality impact, but the patch context does not support arbitrary write or confirmed privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)  SKIP CVE-2026-68420 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: d1716d5a44c37e5743bf6ea4e5cdbdab37727f27 YES  NO NO unknown 	MAYBE	READ KASAN OOB KERNEL_PANIC_PLUS_UAF HARDWARE LINUS SYZBOT  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**

## 2. Signal breakdown

Conservative signals:

* Weak or indirect corruption candidate: +1. The bug is a concrete stack out-of-bounds read in `__xfrm6_addr_hash()` reached from `xfrm_state_find()`.
* Reliable kernel crash or strong DoS: +1. The provided syzbot trace shows a KASAN stack out-of-bounds report from a normal outbound traffic path after the malformed policy is installed.
* Requires CAP_NET_ADMIN in typical deployments: -1. Installing XFRM policies normally requires CAP_NET_ADMIN, but this is not always equivalent to full host root because it may be delegated to container root or network management services.

Paranoid additional signals:

* Local unprivileged trigger in some configurations: +1. If unprivileged user namespaces allow creating a network namespace with CAP_NET_ADMIN, a local unprivileged user may be able to install the malformed XFRM policy in that namespace.
* Confidentiality impact plausible: +1. The primitive is a stack out-of-bounds read, so limited confidentiality concern is defensible, although no direct user-visible disclosure path is shown.
* Common networking packet-processing path: +1. XFRM/IPsec outbound resolution is a kernel networking path and should not be treated as a rare unreachable subsystem once policy setup is possible.

No strong LPE bonus is applied. The patch shows read-only stack OOB access, not UAF reclaim, arbitrary write, callback control, type confusion, or refcount takeover.

## 3. Reachability analysis

The malformed state is created through XFRM policy configuration, so the direct trigger normally requires CAP_NET_ADMIN. After the policy exists, ordinary outbound traffic can reach `xfrm_tmpl_resolve_one()` and `xfrm_state_find()`. The issue is not directly remote reachable because network packets alone do not create the invalid optional IPTFS outbound policy.

Namespaces matter. On systems where untrusted users can create user and network namespaces and gain CAP_NET_ADMIN inside that namespace, the practical privilege requirement may drop from host-admin to local user. Call-site confidence is high because the report includes the failing call chain and the patch changes the validation gate that prevents that path.

## 4. Severity interpretation

This is more than an ordinary validation cleanup because a concrete stack out-of-bounds read is demonstrated in a kernel networking path. Realistic impact is primarily local DoS or KASAN/Oops style failure after privileged or namespace-delegated policy setup. Theoretical confidentiality impact is limited and based on the OOB read class, but the patch does not support integrity impact or privilege escalation.

Overall this is not a Strong Important candidate on the provided evidence, but it is an Actionable Moderate at minimum and should not be auto-closed without manual review.

## 5. One-sentence report phrase

An optional IPTFS template in an outbound XFRM policy can drive the outbound resolution path into a stack out-of-bounds read in `xfrm_state_find()`, causing at least local DoS and requiring manual review because namespace-delegated CAP_NET_ADMIN may reduce the practical privilege barrier.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: concrete stack out-of-bounds read in a kernel networking subsystem, with possible namespace-dependent reachability and limited confidentiality concern, even though no strong LPE primitive is shown.

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

Patch: xfrm: reject optional IPTFS templates in outbound policies [ Upstream
Commit: d7fc6f351c478586980a521d63b0214d9c055e78
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d7fc6f351c478586980a521d63b0214d9c055e78

Changed files:
  net/xfrm/xfrm_user.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=d7fc6f351c478586980a521d63b0214d9c055e78

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

The original Linux kernel CVE announcement for CVE-2026-68420 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68420

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:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS score: 6.1

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: 2
  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: NO
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).