[CVE-2026-46323][IMPORTANT] net: gro: don't merge zcopy skbs [ Upstream

[CVE-2026-46323][IMPORTANT] net: gro: don't merge zcopy skbs [ Upstream

[AL-KERNEL]

CVE: CVE-2026-46323
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: net: gro: don't merge zcopy skbs [ Upstream
Commit: 1f9c828556416fbe3f49386708ce999fc4d4da06
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1f9c828556416fbe3f49386708ce999fc4d4da06
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46323
Analysis date: Tue, 09 Jun 2026 09:13:42 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
`skb_gro_receive() could merge zerocopy skbs with managed fragment references without taking normal page references, leaving GRO skbs pointing to pages whose lifetime is controlled elsewhere and creating a UAF risk in the networking stack.`

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

The original Linux kernel CVE announcement for CVE-2026-46323 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46323

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: IMPORTANT
Manual review required: YES

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

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

CVE-2026-46323	IMPORTANT	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-911;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'skb_gro_receive() could merge zero copy skbs and append frags that are protected by SKBFL_MANAGED_FRAG_REFS without taking normal page references. This can leave the destination GRO skb pointing at pages whose lifetime is managed elsewhere, creating a use after free condition when the original owner releases them. For the CVSS the PR:L is used because reliable triggering appears to require a local process or a local virtual networking path that can create zero copy skb traffic entering GRO, rather than only remote packet delivery. The issue is not treated as directly network reachable from the patch alone, but it is in the network stack and may be exposed in container or virtualization environments. Impact is at least denial of service via kernel crash and in the paranoid case may include confidentiality or integrity impact due to UAF based memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	REMOTE UAF SKB KPANIC 	YES	NO	checked

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

ActionableScore=7
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: **6**
* Paranoid score: **7**
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* **Local unprivileged trigger: +1**
  Reliable triggering appears to require a local process or local virtual networking path capable of producing zerocopy skb traffic that enters GRO.

* **Generic memory corruption, strong corruption primitive: +2**
  The commit explicitly states that appending managed zerocopy fragments without fixing page refcounts can lead to UAF.

* **Real lifetime corruption: +1**
  This is a page lifetime and reference ownership bug involving `SKBFL_MANAGED_FRAG_REFS`.

* **Reliable kernel crash / strong DoS: +1**
  A stale skb frag page reference can plausibly lead to kernel crash when the original owner releases the page.

* **Common networking core path or packet-processing path: +1**
  The bug is in `skb_gro_receive()`, a central GRO packet aggregation path.

* **Hard or special triggering conditions: -1**
  Triggering requires zerocopy skb involvement and GRO merging with managed frag references. This is not a generic remote packet parsing bug.

Conservative total: **6**

Paranoid additional signal:

* **Weak LPE concern: +1**
  UAF in skb fragment lifetime handling may create a memory corruption surface beyond DoS, although no attacker-controlled reclaim, callback overwrite, or object replacement primitive is demonstrated by the patch.

Paranoid total: **7**

## 3. Reachability analysis

The affected path is in the networking GRO receive path, but the patch does not prove that an arbitrary remote packet can directly create the required zerocopy skb state. The more defensible trigger model is local or local-adjacent: a local process, container workload, virtual networking path, or special skb producer creates zerocopy skbs with managed fragment references that later reach GRO merging.

Namespaces and containers may matter because virtual networking and packet injection paths can be exposed to less trusted workloads. This supports **PR:L** in practical triage rather than **PR:H**. The issue should not be treated as directly **AV:N** based only on this patch, but it is still more important than a driver-local crash because it affects core skb lifetime semantics.

## 4. Severity interpretation

This is not an ordinary Moderate cleanup. It is an actionable memory lifetime bug in a central networking path. The realistic impact is likely kernel crash or unstable memory access under specific zerocopy plus GRO conditions. The theoretical impact is higher because the stale skb fragment reference can become a UAF primitive, but the patch does not demonstrate controlled reclaim, arbitrary write, type confusion, or callback control.

Therefore the conservative result is **Actionable Moderate**, and the paranoid result is a **Strong Important candidate** requiring human review.

## 5. One-sentence report phrase

`skb_gro_receive() could merge zerocopy skbs with managed fragment references without taking normal page references, leaving GRO skbs pointing to pages whose lifetime is controlled elsewhere and creating a UAF risk in the networking stack.`

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: this is an explicit UAF candidate in core networking skb fragment lifetime handling. Even though direct remote reachability is not proven, the combination of managed page references, zerocopy skb state, and GRO merging is security-sensitive and should not be auto-closed.

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

Patch: net: gro: don't merge zcopy skbs [ Upstream
Commit: 1f9c828556416fbe3f49386708ce999fc4d4da06
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1f9c828556416fbe3f49386708ce999fc4d4da06

Changed files:
  net/core/gro.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=1f9c828556416fbe3f49386708ce999fc4d4da06

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

The original Linux kernel CVE announcement for CVE-2026-46323 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46323

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:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 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: 6
  Paranoid ActionableScore: 7

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).