[CVE-2026-98241][MODERATE REGULAR] ipv6: xfrm: use full sockets in local error paths

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

CVE: CVE-2026-98241
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ipv6: xfrm: use full sockets in local error paths
Commit: b1a88633c36d2cbc3831382f3846754d344276fd
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b1a88633c36d2cbc3831382f3846754d344276fd
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98241
Analysis date: Fri, 09 Oct 2026 13:09:07 -0400
ActionableScore: 2
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-2026-98241 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98241

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-2026-98241	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98241 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE RESULT=DIFF (independent Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:H';CWE-125;CWE-843;CWE-704;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.5';DESCR 'An out of bounds read can occur in the IPv6 XFRM local error path because xfrm6_local_rxpmtu() and xfrm6_local_error() can treat a TCP_NEW_SYN_RECV request socket as a full IPv6 socket. A remote client can create this state by initiating a TCP connection, while an IPv6 XFRM tunnel route with a lower MTU can direct the SYN ACK into the affected PMTU or local error path. Access through inet_sk() or IPv6 socket state can then read beyond the request socket allocation and may cause a kernel crash. For the CVSS the PR:N value is used because the attacker only needs network access to an exposed IPv6 TCP listener and does not require an authenticated account or local execution on the target. AC:H is used because exploitation depends on a specific XFRM tunnel, rerouting, MTU, and socket ownership state. Impact is at least remote denial of service through a kernel fault. The paranoid score allows limited confidentiality impact from the out of bounds read, but no write primitive, UAF, or supported privilege escalation path is established.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	MAYBE	REMOTE SIMPLEFIX ERRORPATH NETWORK SKB LINUS IPV6  DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN5 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

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

ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Weak or indirect corruption candidate. A `TCP_NEW_SYN_RECV` request socket is incorrectly interpreted as a full inet or IPv6 socket, producing a confirmed heap or slab out-of-bounds read.
* +1 Reliable kernel crash or strong DoS concern. Reading beyond the `request_sock` allocation can reach invalid memory and cause a kernel fault.
* +0 Remote-reachability bonus withheld. Remote TCP traffic can initiate the vulnerable sequence, but the path also depends on a previously configured IPv6 XFRM tunnel route, rerouting, and a lower MTU.
* +0 Confidentiality. No path copying the out-of-bounds bytes to userspace, the network, or another attacker-visible output is established.
* +0 Integrity. The patch establishes reads only. No OOB write, subsequent write, or security-sensitive state modification is shown.
* +0 Strong or weak LPE leverage. There is no UAF, controlled reclaim, attacker-controlled replacement, arbitrary write, callback influence, or privilege-escalation chain.
* +0 Extra availability. The possible kernel crash is already counted once.
* +0 B5-R preservation. B5-R does not apply because there is no heap OOB write, retry-accumulated offset, or later consumption of state corrupted by such a write.
* No negative privilege, race, rarity, or hardware penalties were applied.

3. Reachability analysis

A remote peer can create the relevant `TCP_NEW_SYN_RECV` request socket by initiating an IPv6 TCP connection. The vulnerable callback path additionally requires the target to have an IPv6 XFRM tunnel route whose rerouting and lower MTU cause local PMTU or error handling for the SYN-ACK.

The remote attacker does not need authentication, local execution, or host-administrator privilege once that target configuration exists. Therefore `HostAdminRequired=NO`. The XFRM configuration is prior privileged setup performed by a separate administrator, not a privilege exercised by the remote attacker.

No namespace capability is required by the described attacker, and no namespace-based construction of the complete XFRM path is established. There is no race. The trigger depends on configuration and routing state rather than a narrow timing window. No special hardware is required.

4. Primitive and severity interpretation

The exact primitive is a type confusion followed by a read beyond the allocated `request_sock`. The object remains live, but it is consumed under the wrong socket type. This is not a UAF, stale post-lifetime access, repeated release, refcount mutation, or write primitive.

The demonstrated consequence is an invalid kernel read with possible Oops or panic. Limited confidentiality is theoretically conceivable only if another path exposes the incorrectly read bytes, but no such disclosure path is supplied. Integrity impact and privilege escalation are unsupported.

This is `CLASS_C` because the established behavior is an OOB read and potential crash without an independently useful corruption primitive. `ImportantCandidate=NO` because no write, lifetime corruption, authorization bypass, or attacker-useful semantic reinterpretation is established. `AutoDowngradeAllowed=YES` because the unresolved evidence does not preserve an Important-class primitive.

Likely operational severity is ordinary Moderate for systems using the affected IPv6 XFRM configuration, with remote DoS potential but substantial environmental prerequisites.

5. One-sentence report phrase

A remote IPv6 peer may trigger an out-of-bounds kernel read and possible host crash when an XFRM PMTU error path misinterprets a TCP request socket as a full IPv6 socket, but no write, disclosure, UAF, or privilege-escalation primitive is established.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm whether the affected product deploys reachable IPv6 TCP listeners behind XFRM tunnel routes with the required lower-MTU rerouting and whether downstream error handling exposes any misread data.

7. Call-site confidence

Call-site confidence: high

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

Patch: ipv6: xfrm: use full sockets in local error paths
Commit: b1a88633c36d2cbc3831382f3846754d344276fd
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b1a88633c36d2cbc3831382f3846754d344276fd

Commit description:

xfrm6_local_rxpmtu() and xfrm6_local_error() dereference skb->sk as if it
always pointed at a full IPv6 socket.

That is not guaranteed. TCP SYN-ACK skbs can be owned by a
TCP_NEW_SYN_RECV request_sock while the output path itself is driven by the
full listener. If rerouting selects an IPv6 XFRM tunnel route with a lower
MTU, the local PMTU/error handling path can reach these callbacks with that
mini-socket still attached to the skb.

The callbacks then miscast the request socket as a full inet/IPv6 socket and
can read beyond the request_sock allocation when they access inet_sock or
ipv6_pinfo state.

Resolve the owner with skb_to_full_sk() in both callbacks and bail out when
no full socket is attached. This matches the surrounding XFRM IPv6 PMTU/error
logic, which already reasons about full sockets with skb_to_full_sk().

Fixes: dd76785 ("xfrm6: Don't call icmpv6_send on local error")
Cc: stable@vger.kernel.org
Reported-by: Vega <vega@nebusec.ai>
Signed-off-by: Zhiling Zou <zhilinz@nebusec.ai>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/ipv6/xfrm6_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=b1a88633c36d2cbc3831382f3846754d344276fd

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

The original Linux kernel CVE announcement for CVE-2026-98241 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98241

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:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS score: 6.5

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: 2

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).