[CVE-2026-64004][MODERATE REGULAR] net/iucv: fix locking in .getsockopt [ Upstream

[CVE-2026-64004][MODERATE REGULAR] net/iucv: fix locking in .getsockopt [ Upstream

[AL-KERNEL]

CVE: CVE-2026-64004
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net/iucv: fix locking in .getsockopt [ Upstream
Commit: 884eb247b74d86db97e3a37f0d6fc8e1e83590dd
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=884eb247b74d86db97e3a37f0d6fc8e1e83590dd
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64004
Analysis date: Sun, 19 Jul 2026 19:35:19 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A local AF_IUCV HIPER socket user can race `recvmsg()` with `getsockopt(SO_MSGSIZE)` so that `iucv->hs_dev` is set to NULL before it is dereferenced, causing a kernel NULL pointer dereference and local denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-64004 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64004

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-2026-64004	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-362;CWE-667;**CWE-476;BEST CVSS score: '4.7';DESCR 'A race in AF_IUCV HIPER socket handling can allow getsockopt(SO_MSGSIZE) to dereference iucv hs_dev after a concurrent recvmsg close path has set it to NULL. This produces a NULL pointer dereference and kernel oops, resulting in local denial of service. For the CVSS the PR:L because a local user or local process must be able to use an AF_IUCV HIPER socket and race recvmsg with getsockopt on the affected socket. The issue is not directly network reachable because the trigger is a local socket API race rather than packet processing from a remote peer. Impact is denial of service only based on the available patch context, with no supported evidence of information disclosure, arbitrary write, UAF exploitation, or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	LOCK DANGER NULLPTR SIMPLEFIX  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=2
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. Any local AF_IUCV HIPER user may race `recvmsg()` with `getsockopt(SO_MSGSIZE)`.
* Reliable kernel crash / strong DoS: +1. The described failure is a NULL pointer dereference oops in kernel context.
* Hard or unreliable race / special timing required: -1. The trigger depends on winning a race between socket close handling and `getsockopt()`.
* Rare AND difficult-to-reach subsystem/configuration: -1. AF_IUCV HIPER is s390-specific and not a broad default Linux networking path.

Paranoid interpretation:

* Uses +1 local trigger and +1 crash.
* Does not subtract the rarity/timing penalties as strongly, because the commit says any AF_IUCV HIPER user can potentially crash the kernel.
* No memory corruption, UAF, LPE, confidentiality, or integrity signals are awarded.

No generic memory corruption signal applies. The patch and commit describe a NULL pointer dereference after `hs_dev` is set to NULL, not stale freed-object reuse, UAF reclaim, overwrite, type confusion, callback control, or refcount abuse.

## 3. Reachability analysis

The bug is locally triggerable by a process that can create and use an AF_IUCV HIPER socket and call `recvmsg()` and `getsockopt(SO_MSGSIZE)` concurrently on the affected socket. It is not directly network reachable, because the trigger is a local socket API race rather than packet parsing from a remote peer.

Namespaces do not obviously make this broadly reachable. The affected subsystem is architecture and configuration specific, mainly relevant to s390 IUCV/HIPER environments. There is no evidence that ordinary remote traffic can trigger the bug without a local process using the socket API.

Call-site confidence: high. The patch directly changes `iucv_sock_getsockopt()` and the commit explicitly identifies the racing `recvmsg()` path and the NULL dereference target.

## 4. Severity interpretation

This behaves like an ordinary Moderate / Low-like kernel DoS issue, not an Important-class vulnerability. The theoretical impact is a kernel crash through a race-triggered NULL pointer dereference. The realistic exploitation evidence supports local denial of service only.

There is no supported privilege escalation path. The patch does not show UAF reuse, attacker-controlled reclaim, write-after-free, arbitrary write, type confusion, callback dispatch, information disclosure, or sensitive-object access. Therefore the issue should not be elevated to Actionable Moderate or Important based on the provided evidence.

## 5. One-sentence report phrase

A local AF_IUCV HIPER socket user can race `recvmsg()` with `getsockopt(SO_MSGSIZE)` so that `iucv->hs_dev` is set to NULL before it is dereferenced, causing a kernel NULL pointer dereference and local denial of service.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

This is recommended only because it is a kernel race in a socket subsystem. However, the currently supported primitive is a NULL pointer dereference DoS only, so it does not require urgent Important-class handling.

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

Patch: net/iucv: fix locking in .getsockopt [ Upstream
Commit: 884eb247b74d86db97e3a37f0d6fc8e1e83590dd
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=884eb247b74d86db97e3a37f0d6fc8e1e83590dd

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=884eb247b74d86db97e3a37f0d6fc8e1e83590dd

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

The original Linux kernel CVE announcement for CVE-2026-64004 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64004

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: 1
  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).