[CVE-2026-52985][LOW] netdevsim: zero initialize struct iphdr in dummy sk_buff [ Upstream

[CVE-2026-52985][LOW] netdevsim: zero initialize struct iphdr in dummy sk_buff [ Upstream

[AL-KERNEL]

CVE: CVE-2026-52985
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: netdevsim: zero initialize struct iphdr in dummy sk_buff [ Upstream
Commit: 175556c049eaec14efde8c6475e763b7579b9de7
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=175556c049eaec14efde8c6475e763b7579b9de7
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52985
Analysis date: Wed, 24 Jun 2026 13:50:11 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
`netdevsim used skb_put() instead of skb_put_zero() when building a dummy IPv4 header for devlink trap reporting, which could expose limited uninitialized kernel bytes in a privileged local simulator path.`

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

The original Linux kernel CVE announcement for CVE-2026-52985 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52985

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: LOW
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-2026-52985	LOW	CHECK	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:N';*CWE-457;CWE-908;*CWE-200;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '3.3';DESCR 'netdevsim builds a dummy sk_buff for devlink trap reporting and allocated the IPv4 header with skb_put() without zero initializing the whole struct iphdr. Only selected fields were then written, so remaining header bytes could contain uninitialized kernel memory and trigger KMSAN reports when the skb is processed or reported. For the CVSS the PR:L is used in the paranoid score because a delegated netdevsim or devlink administration context such as CAP_NET_ADMIN in a test or containerized environment may be enough to exercise the path, while the typical base case is PR:H. The issue is not network reachable and requires local control over the netdevsim or devlink test path. Impact is limited confidentiality exposure at most, with no evidence of integrity impact, kernel crash, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	KASAN SIMPLEFIX NETWORK SKB LINUS SYZBOT 	NO	NO	checked

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

ActionableScore=1
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

Conservative signals:

* Confidentiality impact plausible: +1
  Uninitialized bytes in `struct iphdr` could theoretically be exposed through the dummy skb/devlink trap path.
* Requires admin/root/CAP_NET_ADMIN in typical deployments: -2
  `netdevsim` and devlink trap control normally require privileged local administration.
* Rare AND difficult-to-reach subsystem/configuration: -1
  `netdevsim` is a simulator/test driver and is not a normal production data path.

Paranoid adjustment:

* Keep limited confidentiality concern: +1
  Treat the KMSAN uninitialized-value report as a possible limited information exposure, but not as memory corruption.
* Do not add memory corruption, LPE, strong DoS, or network reachability.
  The patch only changes `skb_put()` to `skb_put_zero()` and does not show UAF, OOB write, stale pointer reuse, crash, or privilege escalation.

## 3. Reachability analysis

The bug is locally reachable through the `netdevsim` devlink trap path. In typical deployments, triggering it requires root or CAP_NET_ADMIN-style privileges to create/configure the simulator and related devlink objects. Namespace or container delegation could make this reachable to a less trusted administrative context, but it is still not a normal unprivileged user API. The path is not remote/network-triggerable in the practical sense, despite constructing an skb, because it is a simulator-generated dummy packet rather than packet parsing from an external network peer.

## 4. Severity interpretation

This behaves like a Low-like or ordinary Moderate issue, not an Important-class kernel vulnerability. The realistic impact is limited possible information exposure from uninitialized padding/fields in a dummy IPv4 header. There is no evidence of memory corruption, arbitrary write, reliable kernel crash, UAF, or privilege escalation. The affected subsystem is also uncommon and mostly used for testing.

## 5. One-sentence report phrase

`netdevsim used skb_put() instead of skb_put_zero() when building a dummy IPv4 header for devlink trap reporting, which could expose limited uninitialized kernel bytes in a privileged local simulator path.`

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be auto-closed or handled as low-priority unless the product enables `netdevsim` in a security-sensitive environment with delegated devlink/CAP_NET_ADMIN access.

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

Patch: netdevsim: zero initialize struct iphdr in dummy sk_buff [ Upstream
Commit: 175556c049eaec14efde8c6475e763b7579b9de7
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=175556c049eaec14efde8c6475e763b7579b9de7

Changed files:
  drivers/net/netdevsim/dev.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=175556c049eaec14efde8c6475e763b7579b9de7

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

The original Linux kernel CVE announcement for CVE-2026-52985 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52985

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:L/I:N/A:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
  The Best / paranoid CVSS score: 3.3

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: 0
  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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).