[CVE-2026-98417][MODERATE REGULAR] net: xfrm: reject unrepresentable espintcp transport headers

[CVE-2026-98417][MODERATE REGULAR] net: xfrm: reject unrepresentable espintcp transport headers

[AL-KERNEL]

CVE: CVE-2026-98417
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net: xfrm: reject unrepresentable espintcp transport headers
Commit: d37a5b87577c4b4c1a1dcb000a9dff1df2cf886b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d37a5b87577c4b4c1a1dcb000a9dff1df2cf886b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98417
Analysis date: Wed, 14 Oct 2026 23:12:54 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-98417 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98417

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: NO

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

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-98417	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98417 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE AEGIS_AS=2 LEGACY=MODERATE RESULT=SAME (legacy and Aegis reconciliation agree; DECISION: both MODERATE)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L';CWE-197;CWE-681;*CWE-20;Other CVSS 'AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '3.7';DESCR 'ESP-in-TCP can pass an skb whose transport header offset is no longer representable after the TCP stream parser trims the encapsulation envelope. The unchecked reset can truncate this offset and leave the skb with an incorrect transport header, which reaches an skb warning path and can disrupt XFRM packet processing. For the CVSS the PR:N value is used in the paranoid score because a reachable ESP-in-TCP endpoint might process the malformed stream before meaningful peer authorization, although reliable triggering may instead require access to an established IPsec context. The attack is network reachable but requires a specially arranged packet and skb layout, so AC:H is appropriate. The demonstrated impact is limited availability degradation through warnings and rejected or incorrectly processed packets. There is no concrete UAF, OOB write, information leak, or arbitrary write primitive in the supplied code. Automated impact decision path. The original SimpleNet classifier selected IMPORTANT. The primary LLM estimated paranoid CVSS 3.7 and the production ActionableScore returned 1 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage IMPORTANT to MODERATE_KPANIC because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE_KPANIC to MODERATE because the ActionableScore threshold rule was applied. 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 LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS and DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4. The independent weaker Aegis shadow evaluated CVSS 0.0 and ActionableScore 2 with primitive class CLASS_C and manual review NO. Its independently reconciled impact was MODERATE. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	MAYBE	REMOTE SIMPLEFIX ERRORPATH NETWORK SKB LINUS PACKET  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

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

ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

Positive signals:

* +1 Weak or indirect invalid-state candidate. `skb_reset_transport_header()` truncates an unrepresentable offset, leaving an incorrect transport-header value that reaches later skb processing and its warning path.

Negative or non-awarded signals:

* No negative points were applied.
* Direct remote-reachability +2 was not awarded because ESP-in-TCP requires an already configured XFRM and TCP encapsulation context. The supplied evidence does not establish reachability by an arbitrary unauthenticated Internet host.
* Reliable kernel crash or strong DoS +1 was not awarded. The demonstrated result is an skb warning and packet-processing error, not panic or host-wide failure.
* No UAF, heap OOB write, arbitrary write, controlled reclaim, disclosure, or authorization bypass is established.
* Strong semantic reinterpretation was not awarded. The truncated offset is incorrect active metadata, but no independently useful operation, pointer, descriptor, or ownership primitive is demonstrated.
* B5-R does not apply because there is no confirmed retry-accumulated heap OOB write.
* B3-PENDING does not apply because no shared or file-backed storage write is present.
* B4-PENDING does not apply because no DENY-to-ALLOW authorization decision changes.
* No confidentiality or integrity point was awarded.
* No extra availability point was awarded for the same warning behavior.

Arithmetic:

* Conservative: +1 = 1.
* Paranoid: +1 = 1. Stronger impact would require unsupported evidence of downstream memory access or host-wide DoS.

3. Reachability analysis

A remote ESP-in-TCP peer can influence packets entering this path after the victim has configured the required XFRM and ESP-in-TCP state. Such a peer is below victim host-administrator privilege, so `HostAdminRequired=NO` and `RequiresHostUID0=NO`.

The complete path is not shown to be available to an arbitrary unauthenticated network host. Prior privileged setup of the XFRM policy, security association, and encapsulated transport is expected. The supplied context does not resolve whether that setup can be completed entirely inside attacker-created user and network namespaces, so `NamespaceScopedPrivilege=UNKNOWN`.

There is no special hardware or race prerequisite. Triggering requires an skb layout where trimming the TCP envelope leaves a transport-header offset that exceeds its representable range. This may require specially arranged stream and skb conditions, but the evidence does not establish a narrow timing race.

4. Primitive and severity interpretation

The exact primitive is truncation of an unrepresentable skb transport-header offset, followed by consumption of incorrect header metadata. It is an invalid-state networking bug, not a lifetime violation or confirmed memory-corruption primitive.

There is no stale storage, active-object UAF, repeated release, refcount mutation, or cleanup lifetime defect. The demonstrated consequence is the skb warning path and rejection or disruption of the affected packet. A kernel crash, OOB access, information disclosure, privilege escalation, or useful corruption of adjacent state remains speculative and is not scored.

`PrimitiveClass=CLASS_C` is appropriate because the established behavior is warning and invalid-state handling without an independently useful corruption primitive. `ImportantCandidate=NO` follows from the absence of memory corruption, ownership violation, authorization bypass, or strong DoS. `AutoDowngradeAllowed=YES` because no unresolved Important-preserving primitive is established.

Likely operational severity is Low to ordinary Moderate, depending on how exposed the configured ESP-in-TCP endpoint is and whether repeated malformed traffic causes meaningful log or processing pressure.

5. One-sentence report phrase

An ESP-in-TCP packet can produce an unrepresentable transport-header offset that is truncated into invalid skb metadata and reaches a warning path, but the supplied evidence establishes neither memory corruption nor host-wide denial of service.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm whether an unauthenticated peer can reach `handle_esp()` and whether any downstream path consumes the truncated header before the warning or validation path terminates processing.

7. Call-site confidence

Call-site confidence: medium

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

Patch: net: xfrm: reject unrepresentable espintcp transport headers
Commit: d37a5b87577c4b4c1a1dcb000a9dff1df2cf886b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d37a5b87577c4b4c1a1dcb000a9dff1df2cf886b

Commit description:

ESP-in-TCP can hand xfrm packets whose transport header offset no longer
fits after the stream parser trims the TCP envelope. The plain transport
header reset truncates that offset and triggers the skb warning path.

Use the careful transport-header helper and drop the skb through the
existing XFRM error path when the offset cannot be represented.

Fixes: e27cca9 ("xfrm: add espintcp (RFC 8229)")
Cc: stable@vger.kernel.org
Reported-by: Vega <vega@nebusec.ai>
Assisted-by: Codex:GPT-5.4
Signed-off-by: Wyatt Feng <wf.kernel.dev@gmail.com>
Signed-off-by: Ren Wei <weir@nebusec.ai>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/xfrm/espintcp.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=d37a5b87577c4b4c1a1dcb000a9dff1df2cf886b

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

The original Linux kernel CVE announcement for CVE-2026-98417 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98417

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:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS score: 3.7

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: 1

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