[CVE-2026-68140][IMPORTANT] net/iucv: fix use-after-free of a severed iucv_path

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

CVE: CVE-2026-68140
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: net/iucv: fix use-after-free of a severed iucv_path
Commit: 23658b350b4107e8292045c2044983fd426fa15d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=23658b350b4107e8292045c2044983fd426fa15d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68140
Analysis date: Mon, 10 Aug 2026 11:08:06 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
AF_IUCV can retain queued message notifications that reference a freed `iucv_path` after peer sever, allowing a later `recvmsg()` to trigger a kernel use-after-free and likely DoS, with manual review needed for possible higher impact in affected z/VM style deployments.

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

The original Linux kernel CVE announcement for CVE-2026-68140 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68140

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.

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

CVE-2026-68140	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-416;*CWE-672;*CWE-664;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.5';DESCR 'AF_IUCV can use a freed iucv_path because message notifications kept on message_q store a raw path pointer and are not removed when the peer severs the connection. After iucv_sever_path frees the path, a later recvmsg can drain the queued notification through iucv_process_message_q and pass the stale pointer to message_receive, producing a use after free in kernel context. For the CVSS the PR:N is used for the paranoid score because an attacking IUCV peer does not need an account or privileges on the victim system beyond the ability to establish or influence the IUCV connection. The issue is adjacent network reachable in z VM or similar IUCV deployments rather than public Internet reachable. Impact is at least denial of service via kernel crash, and the UAF primitive makes limited or high confidentiality and integrity impact plausible enough for manual review.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	LOCK LEAK UAF  KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	NO	NO	checked

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

ActionableScore=7
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Remote or cross-VM reachable influence: +2
  AF_IUCV is not public Internet reachable, but the triggering peer can influence the connection lifecycle from another IUCV endpoint in z/VM-like deployments.
* Generic memory corruption, UAF: +2
  Queued notifications retain a raw pointer to `iucv_path` after `iucv_path_free()`.
* Real lifetime corruption: +1
  This is a stale pointer after free, later consumed by `recvmsg()` through `iucv_process_message_q()`.
* Reliable kernel crash / strong DoS: +1
  Passing the freed path into `message_receive()` is a credible kernel crash path.
* Rare AND difficult-to-reach subsystem/configuration: -1
  AF_IUCV is mainly relevant on s390 / z/VM style deployments, not broad default networking.

Conservative total: 5

Paranoid additional signals:

* Weak LPE concern: +1
  This is a real kernel UAF, not just a NULL dereference. No reclaim or overwrite primitive is shown, so this is weak rather than strong LPE plausibility.
* Confidentiality impact plausible: +1
  Plausible only under UAF reuse assumptions, not demonstrated.
* Integrity impact plausible: +1
  Plausible only under UAF reuse assumptions, not demonstrated.

Paranoid total before keeping grounded: 8, reduced to 7 because the patch does not show attacker-controlled reclaim, overwrite, callback control, or type confusion.

## 3. Reachability analysis

The bug can be influenced by an AF_IUCV peer that severs a connection after message notifications have been queued. A later local `recvmsg()` on the victim socket can drain the stale queued notification and pass the freed `iucv_path` into the receive path.

This is not ordinary Internet remote exposure. It is best treated as adjacent or cross-VM reachable in environments where AF_IUCV is used, such as s390 / z/VM communication setups. No local account on the victim is necessarily required for the peer-side influence, so PR:N is defensible for the paranoid CVSS interpretation. In deployments without AF_IUCV exposure or without untrusted IUCV peers, practical reachability is much lower.

Namespaces and containers are unlikely to be the primary exposure reducer here. The more important gating factor is whether AF_IUCV is available and whether untrusted peers can connect or sever paths.

Call-site confidence: high. The commit explicitly describes the stale pointer path from `message_q` through `iucv_process_message_q()` to `message_receive()` after `iucv_path_free()`.

## 4. Severity interpretation

This is stronger than an ordinary Moderate because it is a concrete kernel use-after-free in a communication subsystem, with peer-influenced lifetime ordering and a credible crash path.

Realistic demonstrated impact is DoS through kernel crash. Privilege escalation is not proven because the patch does not show attacker-controlled reclaim, object replacement, write-after-free, callback dispatch, or refcount takeover. However, because the stale pointer is passed back into kernel receive handling, the UAF class is serious enough to avoid auto-closure and warrants manual review.

Overall, this is an Actionable Moderate at minimum and a Strong Important candidate under paranoid triage.

## 5. One-sentence report phrase

AF_IUCV can retain queued message notifications that reference a freed `iucv_path` after peer sever, allowing a later `recvmsg()` to trigger a kernel use-after-free and likely DoS, with manual review needed for possible higher impact in affected z/VM style deployments.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a real stale-pointer UAF in kernel context with adjacent peer influence. Even though practical LPE is not demonstrated, the lifetime primitive is concrete and should not be auto-closed.

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

Patch: net/iucv: fix use-after-free of a severed iucv_path
Commit: 23658b350b4107e8292045c2044983fd426fa15d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=23658b350b4107e8292045c2044983fd426fa15d

Commit description:

af_iucv queues not-yet-received message notifications on iucv->message_q,
each holding a raw pointer to the connection's iucv_path.  When the peer
severs the connection, iucv_sever_path() frees that path with
iucv_path_free() but leaves the notifications queued.  A later recvmsg()
drains message_q via iucv_process_message_q() and hands the stale path to
message_receive() -- a use-after-free of the freed iucv_path.

Drop the queued notifications when the path is severed; once the path is
gone they can no longer be received.  This also frees the notifications
leaked when a socket is closed with messages still queued.

Fixes: f0703c8 ("[AF_IUCV]: postpone receival of iucv-packets")
Closes: https://sashiko.dev/#/patchset/20260705-b4-disp-fc79c0dc-v1-1-d2cdcb57afa9@proton.me?part=1
Cc: stable@vger.kernel.org
Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
Link: https://patch.msgid.link/20260707-b4-disp-783fedbb-v1-1-463b9dbda2ea@proton.me
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/iucv/af_iucv.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=23658b350b4107e8292045c2044983fd426fa15d

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

The original Linux kernel CVE announcement for CVE-2026-68140 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68140

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:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.5

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: 5
  Paranoid ActionableScore: 7

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).