[CVE-2023-53186][IMPORTANT] skbuff: Fix a race between coalescing and releasing SKBs [ Upstream

[CVE-2023-53186][IMPORTANT] skbuff: Fix a race between coalescing and releasing SKBs [ Upstream

[AL-KERNEL]

CVE: CVE-2023-53186
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: skbuff: Fix a race between coalescing and releasing SKBs [ Upstream
Commit: 906a6689bb0191ad2a44131a3377006aa098af59
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=906a6689bb0191ad2a44131a3377006aa098af59
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2023-53186
Analysis date: Mon, 06 Jul 2026 14:27:02 -0400
ActionableScore: 8
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate
Manual review required: YES

Summary:
A race between SKB coalescing and cloned page_pool SKB release can corrupt page reference counts, leading to UAF or double-free and a remotely influenced kernel crash on affected networking configurations.

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

The original Linux kernel CVE announcement for CVE-2023-53186 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2023-53186

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
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CVE-2023-53186	IMPORTANT	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';CWE-362;*CWE-416;CWE-415;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '8.1';DESCR 'A race in skb_try_coalesce() can occur when a cloned SKB backed by page_pool pages is coalesced while another clone is released. The release path can clear fragment state before the coalescing path takes the expected page reference, leaving inconsistent page refcounts and later causing use-after-free or double-free when the merged SKB is released. For the CVSS the PR:N is used because the paranoid interpretation treats the bug as reachable by packet traffic on a configured NIC path without credentials on the victim. The issue is network reachable only under specific page_pool, cloning, and coalescing conditions, so AC:H is used. Impact is at least denial of service via kernel crash, and worst case may allow confidentiality or integrity impact because the primitive is race driven UAF or double-free in core networking memory management. YES REQUIRES MANUAL CHECK';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate (with actual score 7)	YES	REMOTE DANGER RACE UAF SKB HARDWARE LINUS CVEOUTDATED KPANIC 	YES	YES	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=8
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: 6
* Paranoid score: 8
* Final recommended bucket: **Strong Important candidate**::

## 2. Signal breakdown

Conservative score signals:

* Remote reachable / network-triggerable: +2. The affected code is in core SKB networking receive/coalescing logic and can plausibly be influenced by packet traffic on affected NIC/page_pool paths.
* Generic memory corruption, strong primitive: +2. The commit explicitly describes use-after-free and double-free outcomes.
* Real lifetime corruption: +1. The bug is caused by incorrect page reference lifetime handling when a cloned SKB is released during coalescing.
* Reliable kernel crash / strong DoS: +1. The reported failure is bad page state with negative refcount and crash in the RX softirq path.
* Common networking core path: +1. The affected function is in `net/core/skbuff.c`.
* Hard race / special timing required: -1. Triggering requires a race between coalescing and release of another SKB clone.
* Configuration-dependent exposure: -1. Practical exposure depends on page_pool fragment recycling, cloned SKBs, suitable driver behavior, and coalescing conditions.

Paranoid additions:

* Weak to strong LPE concern: +1. UAF/double-free in SKB/page_pool memory management may be security relevant beyond DoS, although no reliable reclaim or controlled overwrite primitive is demonstrated.
* Confidentiality impact plausible: +1. Kernel memory lifetime corruption may theoretically expose data depending on allocator reuse.
* Integrity impact plausible: +1. Double-free/UAF can corrupt kernel memory state in worst-case layouts.

## 3. Reachability analysis

A remote sender may influence this path through packet traffic, but only on systems where the NIC driver and network stack use page_pool fragment recycling and where SKB cloning plus coalescing happen in the required timing window. No credentials are required for the remote packet source in the paranoid interpretation. Containers do not materially change the remote trigger, but local container workloads may increase traffic patterns that exercise the path. This is not universally reachable on all hosts because it depends on driver, page_pool, and timing conditions.

## 4. Severity interpretation

This behaves as an actionable Moderate conservatively and a Strong Important candidate in paranoid triage. The demonstrated impact is a race-driven refcount/lifetime bug causing UAF or double-free and kernel crash. Practical exploitation beyond DoS is not demonstrated, but the primitive is serious because it affects core networking memory management and may be remotely influenced under realistic high-performance NIC configurations.

## 5. One-sentence report phrase

A race between SKB coalescing and cloned page_pool SKB release can corrupt page reference counts, leading to UAF or double-free and a remotely influenced kernel crash on affected networking configurations.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: explicit UAF/double-free in a core networking path with plausible packet influence should not be auto-closed, even though exploitation requires page_pool, SKB cloning, coalescing, and a difficult timing window.

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

Patch: skbuff: Fix a race between coalescing and releasing SKBs [ Upstream
Commit: 906a6689bb0191ad2a44131a3377006aa098af59
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=906a6689bb0191ad2a44131a3377006aa098af59

Changed files:
  net/core/skbuff.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=906a6689bb0191ad2a44131a3377006aa098af59

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

The original Linux kernel CVE announcement for CVE-2023-53186 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2023-53186

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:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 8.1

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: 6
  Paranoid ActionableScore: 8

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).