[CVE-2026-52942][MODERATE 7.0] netfilter: nf_log: validate MAC header was set before dumping it [ Upstream

[CVE-2026-52942][MODERATE 7.0] netfilter: nf_log: validate MAC header was set before dumping it [ Upstream

[AL-KERNEL]

CVE: CVE-2026-52942
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: netfilter: nf_log: validate MAC header was set before dumping it [ Upstream
Commit: d704ee9c7bc68a161684c51a7ac05b446dcf38d4
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d704ee9c7bc68a161684c51a7ac05b446dcf38d4
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52942
Analysis date: Wed, 24 Jun 2026 04:01:45 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A local CAP_NET_RAW capable process can trigger a netfilter nf_log out-of-bounds read through AF_PACKET with PACKET_QDISC_BYPASS when netdev logging is configured, leaking kernel memory bytes into logs and potentially causing a kernel crash.

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

The original Linux kernel CVE announcement for CVE-2026-52942 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52942

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 7.0
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-2026-52942	MODERATE	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:H/I:N/A:H';CWE-125;*CWE-200;*CWE-20;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:L';BEST CVSS score: '7.1';DESCR 'An out of bounds read in the netfilter nf_log MAC header dump path occurs because dump_mac_header() can use skb_mac_header() when the skb MAC header was never set. A local process can reach this path through AF_PACKET with PACKET_QDISC_BYPASS when a netdev logging rule logs the packet, causing bytes outside the skb buffer to be copied into the kernel log and potentially causing a kernel crash on hardened or debug builds. For the CVSS the PR:L value is used because reliable triggering requires local code execution with packet socket capability such as CAP_NET_RAW or an equivalent delegated network context, not full administrator privileges. The issue is not remotely reachable by ordinary network traffic because the unset MAC header state is created by the local packet transmit path. Impact is primarily local information disclosure through kernel logs and possible denial of service, with no supported write primitive or direct privilege escalation shown by the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	REMOTE READ KASAN OOB NETFILTER SKB TEST QDISC PACKET  KPANIC INCREASED_TO_MODERATE7_FROM_MODERATE_BASED_ON_GUESSCVSS	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**

## 2. Signal breakdown

Conservative signals:

* Local low-privilege trigger: +1
  The described trigger uses AF_PACKET with PACKET_QDISC_BYPASS. This usually requires CAP_NET_RAW or an equivalent delegated packet-socket capability, but not full host root.

* Confidentiality impact plausible: +1
  The bug reads bytes out of bounds from kernel memory and writes them into the kernel log via nf_log. This is a real disclosure sink, although practical attacker access to logs depends on dmesg and journal permissions.

* Availability impact realistic: +1
  KASAN reports a slab-out-of-bounds read in dump_mac_header(). On hardened, debug, or unlucky production layouts, this can become a kernel crash or panic-like DoS.

* Common packet-processing path: +1
  The affected code is in netfilter logging on the packet path. The exact trigger requires a netdev logging rule, but the subsystem is security-sensitive and commonly deployed.

Paranoid additional signal:

* Reliable kernel crash / strong DoS concern: +1
  The provided trace shows a concrete KASAN OOB read from the exploit task. If panic_on_oops, panic_on_warn, KASAN, or hardened memory checking is enabled, the DoS impact becomes more reliable.

Not counted:

* No remote reachable signal. Ordinary remote packets do not create the unset skb MAC header state in this path.
* No generic strong memory corruption signal. This is an OOB read, not an OOB write, UAF, double-free, or type confusion.
* No privilege escalation signal. The patch context does not show attacker-controlled write, reclaim, callback control, or object replacement.

## 3. Reachability analysis

A local process can trigger the vulnerable path by sending through AF_PACKET with PACKET_QDISC_BYPASS, provided packet logging through the netdev logger is active. In typical deployments, AF_PACKET requires CAP_NET_RAW, so this is best treated as PR:L rather than PR:N. If the attacker also needs to create the nftables or netfilter logging rule, CAP_NET_ADMIN would be required, lowering practical exposure. However, if such logging is already configured by the administrator, a lower-privileged local process with packet-socket capability may be sufficient.

Namespaces and containers matter. Container root or a service with CAP_NET_RAW in a network namespace may be able to generate the packet condition, but the vulnerable logging path must exist in that namespace or on a reachable configured netdev hook. This is not directly reachable from the network because the malformed skb state is created by a local transmit path that bypasses normal MAC header setup.

## 4. Severity interpretation

This behaves more like an actionable Moderate than an ordinary low-risk Moderate. The realistic primitive is an out-of-bounds kernel read with disclosure into logs and possible DoS, not arbitrary memory corruption. The theoretical risk is higher than a simple warning or validation bug because the OOB read is concrete and demonstrated by KASAN, but the patch does not support treating it as LPE or Important-class memory corruption.

The main reason not to auto-close is that the bug combines netfilter packet-path reachability, local packet-socket control, and a real kernel memory disclosure sink. The main reason not to classify it as Strong Important is the lack of write primitive, UAF, object lifetime control, or direct remote reachability.

## 5. One-sentence report phrase

A local CAP_NET_RAW capable process can trigger a netfilter nf_log out-of-bounds read through AF_PACKET with PACKET_QDISC_BYPASS when netdev logging is configured, leaking kernel memory bytes into logs and potentially causing a kernel crash.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Manual review is required because this is a concrete kernel OOB read with a disclosure sink into kernel logs and a demonstrated KASAN failure. It should not be treated as pure DoS, but current evidence does not justify LPE or strong memory-corruption classification.

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

Patch: netfilter: nf_log: validate MAC header was set before dumping it [ Upstream
Commit: d704ee9c7bc68a161684c51a7ac05b446dcf38d4
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d704ee9c7bc68a161684c51a7ac05b446dcf38d4

Changed files:
  net/netfilter/nf_log_syslog.c
  mm/kasan/report.c
  net/netfilter/nf_log.c
  net/netfilter/nft_log.c
  net/netfilter/nf_tables_core.c
  net/netfilter/nft_chain_filter.c
  net/netfilter/core.c
  net/packet/af_packet.c
  net/socket.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=d704ee9c7bc68a161684c51a7ac05b446dcf38d4

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

The original Linux kernel CVE announcement for CVE-2026-52942 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52942

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:H/PR:L/UI:N/S:U/C:L/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
  The Best / paranoid CVSS score: 7.1

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: 4
  Paranoid ActionableScore: 5

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).