[CVE-2026-72019][MODERATE 7.0] macsec: don't read an unset MAC header in macsec_encrypt()

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

CVE: CVE-2026-72019
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: macsec: don't read an unset MAC header in macsec_encrypt()
Commit: dc9ffa1905e72f026d080880a2e4cfc42aa91000
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dc9ffa1905e72f026d080880a2e4cfc42aa91000
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72019
Analysis date: Sat, 15 Aug 2026 02:55:59 -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 MACsec TX path heap over-read by sending AF_PACKET SOCK_RAW traffic with PACKET_QDISC_BYPASS, causing 12 bytes of kernel heap data to be emitted in outer MAC address fields and making this an actionable information disclosure issue.

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

The original Linux kernel CVE announcement for CVE-2026-72019 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72019

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-2026-72019	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	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:L';CWE-125;CWE-126;*CWE-200;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:L';BEST CVSS score: '6.1';DESCR 'macsec_encrypt can read an unset skb MAC header when an AF_PACKET SOCK_RAW transmit path with PACKET_QDISC_BYPASS reaches the MACsec ndo_start_xmit path. The wrong header helper can make eth_hdr(skb) point outside the valid packet data, causing a 12-byte heap over-read whose bytes are copied into the outer source and destination MAC fields and emitted on the wire. For the CVSS the PR:L is selected because triggering requires a local process with AF_PACKET SOCK_RAW capability such as CAP_NET_RAW, not full administrator control in all deployments. The issue is not directly network reachable by a remote host, but leaked bytes may be observable on the adjacent network segment where MACsec traffic is sent. Impact is primarily confidentiality loss from kernel heap disclosure, with possible denial of service on debug or sanitizer builds. For the paranoid score, the highest still-defensible interpretation is C:H/I:N/A:L because repeated frames may disclose more heap data, while no write primitive or privilege escalation path is shown.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	READ KASAN OOB SIMPLEFIX NETWORK SKB QDISC PACKET  DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	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. Triggering requires a local process able to use AF_PACKET SOCK_RAW and PACKET_QDISC_BYPASS, typically CAP_NET_RAW or delegated equivalent, not full host root.
* Confidentiality impact plausible: +1. The bug causes a 12-byte kernel heap over-read and the bytes are copied into transmitted outer MAC address fields.
* Packet-processing path exposure: +1. The bug is in the MACsec TX path and affects skb header handling during packet transmission.
* Manual-review information disclosure relevance: +1. The over-read is not only detected by KASAN, it is emitted on the wire, making it a real disclosure primitive.

Paranoid additional signal:

* Availability impact in hardened/debug configurations: +1. KASAN reports slab-out-of-bounds and CONFIG_DEBUG_NET detects unset MAC header use. This is not a strong production DoS by itself, but it can become crash-relevant with panic_on_warn or sanitizer/debug deployments.

Not counted:

* No remote trigger: +0. A remote host cannot directly invoke this path.
* No strong memory corruption: +0. This is a read-only OOB, not OOB write, UAF, double-free, type confusion, or arbitrary write.
* No LPE signal: +0. The patch does not show attacker-controlled overwrite, reclaim, callback control, or privilege escalation primitive.
* No CAP_SYS_ADMIN/CAP_NET_ADMIN penalty: 0. Triggering packet transmission is closer to CAP_NET_RAW/delegated packet access than full administrative control, although MACsec deployment itself is configuration-dependent.
* Rare configuration penalty not applied strongly. MACsec is not default everywhere, but this is still a normal networking data path once configured.

## 3. Reachability analysis

The realistic trigger is local: a process sends through an existing MACsec device using AF_PACKET SOCK_RAW with PACKET_QDISC_BYPASS so the skb reaches macsec_encrypt() with skb->mac_header unset. This usually requires CAP_NET_RAW or an equivalent delegated capability. It is not directly network-reachable because incoming packets from a remote host do not cause the vulnerable transmit-side AF_PACKET path.

Namespaces and containers may matter if CAP_NET_RAW is delegated or if a container can access the relevant MACsec interface. In normal locked-down deployments this is less exposed, but reduced-capability service accounts or containers with raw packet access should not be treated as full host root.

## 4. Severity interpretation

This behaves more like an actionable Moderate than an Important memory-corruption issue. The demonstrated primitive is a limited OOB read of 12 bytes, but the important detail is that the bytes are transmitted on the wire, so confidentiality impact is plausible rather than purely theoretical.

There is no evidence of integrity impact or privilege escalation. The paranoid score is elevated only because repeated triggering may disclose more heap bytes and hardened/debug kernels may convert the warning/OOB read into a crash-relevant condition.

## 5. One-sentence report phrase

A local CAP_NET_RAW capable process can trigger a MACsec TX path heap over-read by sending AF_PACKET SOCK_RAW traffic with PACKET_QDISC_BYPASS, causing 12 bytes of kernel heap data to be emitted in outer MAC address fields and making this an actionable information disclosure issue.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a kernel heap out-of-bounds read with user-triggerable disclosure on the wire. It is not merely a warning or local crash, and exposure depends on MACsec deployment plus CAP_NET_RAW delegation, which should be verified manually.

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

Patch: macsec: don't read an unset MAC header in macsec_encrypt()
Commit: dc9ffa1905e72f026d080880a2e4cfc42aa91000
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dc9ffa1905e72f026d080880a2e4cfc42aa91000

Commit description:

macsec_encrypt() reads the Ethernet header via eth_hdr(skb)
(skb->head + skb->mac_header) to memmove() the 12 source/destination MAC
bytes forward and make room for the SecTAG.

On the AF_PACKET SOCK_RAW + PACKET_QDISC_BYPASS transmit path the skb
reaches the macsec ndo_start_xmit() with the MAC header unset, so
eth_hdr(skb) resolves to skb->head + (u16)~0 and the read is out of
bounds: a 12-byte heap over-read that is also emitted on the wire as the
frame's outer source/destination MAC. KASAN reports a slab-out-of-bounds
read in macsec_start_xmit() on 6.0; on current mainline a CONFIG_DEBUG_NET
build flags it as an unset mac header in skb_mac_header().

On the TX path the L2 header is at skb->data, so use skb_eth_hdr(), added
by commit 96cc4b6 ("macvlan: do not assume mac_header is set in
macvlan_broadcast()") for exactly this purpose.

Fixes: c09440f ("macsec: introduce IEEE 802.1AE driver")
Cc: stable@vger.kernel.org
Signed-off-by: Daehyeon Ko <4ncienth@gmail.com>
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Link: https://patch.msgid.link/20260703083634.2035145-1-4ncienth@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/net/macsec.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=dc9ffa1905e72f026d080880a2e4cfc42aa91000

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

The original Linux kernel CVE announcement for CVE-2026-72019 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72019

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: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:L
  The Best / paranoid CVSS score: 6.1

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: NO
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).