[CVE-2026-46132][MODERATE 7.0] net: rtnetlink: zero ifla_vf_broadcast to avoid stack infoleak in rtnl_fill_vfinfo

[CVE-2026-46132][MODERATE 7.0] net: rtnetlink: zero ifla_vf_broadcast to avoid stack infoleak in rtnl_fill_vfinfo

[AL-KERNEL]

CVE: CVE-2026-46132
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: net: rtnetlink: zero ifla_vf_broadcast to avoid stack infoleak in rtnl_fill_vfinfo
Commit: 0653c0516234c8258975d268a749115fc0f0ff00
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0653c0516234c8258975d268a749115fc0f0ff00
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46132
Analysis date: Thu, 28 May 2026 13:29:52 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: NO

Summary:
An unprivileged local `RTM_GETLINK` request with VF filtering can leak up to 26 bytes of uninitialized kernel stack per VF through `IFLA_VF_BROADCAST`, potentially exposing kernel pointers or transient stack data.

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

The original Linux kernel CVE announcement for CVE-2026-46132 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46132

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: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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

CVE-2026-46132	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:N';*CWE-200;CWE-908;*CWE-457;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '5.5';DESCR 'rtnetlink VF info generation used an uninitialized stack based ifla_vf_broadcast structure and copied only dev addr_len bytes into its 32 byte broadcast field. On typical Ethernet devices this writes 6 bytes and leaves up to 26 bytes of kernel stack residue that can be returned to userspace through RTM_GETLINK with RTEXT_FILTER_VF. For the CVSS the PR:L is used because a local unprivileged process can use AF_NETLINK / NETLINK_ROUTE, but local code execution is still required. The issue is not network reachable and does not provide a write primitive or direct privilege escalation path. Impact is confidentiality only. The base score uses C:L, while the paranoid score uses C:H because the leak is repeatable per VF and may expose kernel pointers or transient sensitive stack data useful for follow on attacks.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5) 	MAYBE	REMOTE KASAN LEAK HARDWARE LINUS  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK	-	-	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

* Local unprivileged trigger: **+1**. Any local unprivileged process can open `AF_NETLINK / NETLINK_ROUTE` and issue `RTM_GETLINK` with `RTEXT_FILTER_VF`.
* Confidentiality impact plausible: **+1**. Up to 26 bytes of uninitialized kernel stack can be returned to userspace per VF per request.
* Broad/default/common subsystem exposure: **+1**. `rtnetlink` is a core networking control-plane interface, although the specific leak requires VF information to be present.
* Local netlink kernel interface: **+1**. The trigger is an unprivileged netlink query path that can be repeated and shaped through request attributes.
* Repeatable stack leak concern, paranoid: **+1**. The leak is repeatable and stack residue may include kernel pointers or transient sensitive data useful for follow-on attacks.
* No memory corruption: **+0**. This is an info leak, not OOB write, UAF, double-free, or heap overwrite.
* No direct LPE primitive: **+0**. The patch does not show direct privilege escalation, but the leak may weaken mitigations such as KASLR.

## 3. Reachability analysis

The bug is locally reachable by an unprivileged process through `NETLINK_ROUTE`. It does not require `CAP_NET_ADMIN` for the described `RTM_GETLINK` query. Containers may matter if they can access netlink link information for devices exposing VF data, but practical leakage depends on SR-IOV or VF information being visible in the namespace. The issue is not remotely network-triggerable by packets. Realistic exploitation requires a system with VF info exposed, then repeated local netlink queries can harvest small stack fragments.

## 4. Severity interpretation

This behaves like an **Actionable Moderate** issue. It is not memory corruption and does not directly provide code execution or privilege escalation. However, it is a repeatable unprivileged kernel stack information leak in a core netlink path, and leaked stack bytes may assist exploitation of other bugs. This should not be treated as Important by itself, but it should not be auto-closed as a harmless functional bug.

## 5. One-sentence report phrase

An unprivileged local `RTM_GETLINK` request with VF filtering can leak up to 26 bytes of uninitialized kernel stack per VF through `IFLA_VF_BROADCAST`, potentially exposing kernel pointers or transient stack data.

## 6. Manual review recommendation

**MANUAL CHECK RECOMMENDED**

Manual review is recommended because this is a repeatable unprivileged kernel stack info leak in `rtnetlink`, although there is no direct memory corruption or standalone privilege-escalation primitive.

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

Patch: net: rtnetlink: zero ifla_vf_broadcast to avoid stack infoleak in rtnl_fill_vfinfo
Commit: 0653c0516234c8258975d268a749115fc0f0ff00
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0653c0516234c8258975d268a749115fc0f0ff00

Commit description:

rtnl_fill_vfinfo() declares struct ifla_vf_broadcast on the stack
without initialisation:

	struct ifla_vf_broadcast vf_broadcast;

The struct contains a single fixed 32-byte field:

	/* include/uapi/linux/if_link.h */
	struct ifla_vf_broadcast {
		__u8 broadcast[32];
	};

The function then copies dev->broadcast into it using dev->addr_len
as the length:

	memcpy(vf_broadcast.broadcast, dev->broadcast, dev->addr_len);

On Ethernet devices (the overwhelming majority of SR-IOV NICs)
dev->addr_len is 6, so only the first 6 bytes of broadcast[] are
written. The remaining 26 bytes retain whatever was previously on
the kernel stack. The full struct is then handed to userspace via:

	nla_put(skb, IFLA_VF_BROADCAST,
		sizeof(vf_broadcast), &vf_broadcast)

leaking up to 26 bytes of uninitialised kernel stack per VF per
RTM_GETLINK request, repeatable.

The other vf_* structs in the same function are explicitly zeroed
for exactly this reason - see the memset() calls for ivi,
vf_vlan_info, node_guid and port_guid a few lines above.
vf_broadcast was simply missed when it was added.

Reachability: any unprivileged local process can open AF_NETLINK /
NETLINK_ROUTE without capabilities and send RTM_GETLINK with an
IFLA_EXT_MASK attribute carrying RTEXT_FILTER_VF. The kernel walks
each VF and emits IFLA_VF_BROADCAST, leaking 26 bytes of stack per
VF per request. Stack residue at this call site can include return
addresses and transient sensitive data; KASAN with stack
instrumentation, or KMSAN, will flag the nla_put() when reproduced.

Zero the on-stack struct before the partial memcpy, matching the
existing pattern used for the other vf_* structs in the same
function.

Fixes: 75345f8 ("ipoib: show VF broadcast address")
Cc: stable@vger.kernel.org
Signed-off-by: Kai Zen <kai.aizen.dev@gmail.com>
Link: https://patch.msgid.link/3c506e8f936e52b57620269b55c348af05d413a2.1777557228.git.kai.aizen.dev@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  include/uapi/linux/if_link.h
  net/core/rtnetlink.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=0653c0516234c8258975d268a749115fc0f0ff00

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

The original Linux kernel CVE announcement for CVE-2026-46132 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46132

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:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
  The Best / paranoid CVSS score: 5.5

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: 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).