[CVE-2026-53033][IMPORTANT] bpf, sockmap: Take state lock for af_unix iter [ Upstream

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

CVE: CVE-2026-53033
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: bpf, sockmap: Take state lock for af_unix iter [ Upstream
Commit: c6f4015eac2e3cbc3cb7a17539e10bbb5c2049c3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c6f4015eac2e3cbc3cb7a17539e10bbb5c2049c3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53033
Analysis date: Thu, 25 Jun 2026 10:58:33 -0400
ActionableScore: 8
ActionableScore lower bound: 7
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race between the AF_UNIX BPF iterator sockmap update path and concurrent socket close can leave a stale peer socket pointer and cause a slab use-after-free write in kernel socket memory, allowing at least local DoS and plausibly privilege escalation in capability-delegated BPF environments.

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

The original Linux kernel CVE announcement for CVE-2026-53033 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53033

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-2026-53033	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-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in the af_unix BPF iterator and sockmap update path can leave unix_stream_bpf_update_proto using a stale peer socket pointer while another task closes the paired UNIX socket. The stale pointer can be passed to sock_hold after unix_release_sock has dropped the peer reference, producing a slab use-after-free with a kernel write to freed socket memory. For the CVSS the PR:L value is used because triggering requires a local process with access to BPF iterator and sockmap operations, but not necessarily full root in deployments that delegate BPF or network capabilities. The issue is not directly network reachable and requires local code execution. Impact is at least a local denial of service via kernel crash and in the paranoid case may allow confidentiality and integrity impact due to kernel memory corruption, so C:H/I:H/A:H is defensible for manual-review sensitivity.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8) 	MAYBE	REMOTE NULLPTR BPF RACE UAF HARDWARE TEST  KPANIC INCREASED_TO_MODERATE7_FROM_MODERATE_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	-	-	checked

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

ActionableScore=8
ActionableScoreLower=7

## 1. ActionableScore

* Conservative score: **7**
* Paranoid score: **8**
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* **Memory corruption, Strong corruption primitive: +2**
  KASAN confirms a real slab-use-after-free in `unix_stream_bpf_update_proto()`.

* **Real lifetime corruption: +1**
  The bug is a stale `peer` socket pointer after `unix_release_sock()` clears `unix_peer(sk)` and drops the reference.

* **Weak to strong LPE concern: +1 conservative, +2 paranoid**
  Conservative view: UAF write is shown, but no reclaim/control primitive is demonstrated. Paranoid view: UAF on `struct sock` with a write via `sock_hold()` is security-relevant enough to treat privilege escalation as plausible.

* **Reliable kernel crash / strong DoS: +1**
  The report includes a concrete KASAN UAF trace and kernel memory write after free.

* **Local high-control kernel data-plane API: +1**
  Trigger path involves BPF iterator plus sockmap update, a high-control local kernel API surface.

* **Confidentiality impact plausible: +1 paranoid-sensitive**
  UAF on socket objects may allow object reuse or stale object interaction in a worst-case analysis, although no direct leak is demonstrated.

* **Integrity impact plausible: +1 paranoid-sensitive**
  The observed operation writes to freed kernel socket memory, so integrity impact is plausible beyond a pure crash.

* **Hard or unreliable race / timing window: -1**
  The bug requires overlap between BPF iterator sockmap update and concurrent UNIX socket close.

* **Requires privileged or delegated BPF capability in typical deployments: -1 conservative**
  BPF iterator and sockmap operations are commonly restricted, but delegated BPF or container/service capability models can reduce this below full host-root.

## 3. Reachability analysis

The bug is locally reachable by a process that can run a BPF iterator program and update a sockmap while another task closes the paired UNIX socket. It is not directly network reachable. Typical production systems restrict this path through BPF-related capabilities or sysctls, but containerized or delegated-capability environments may expose it to non-root service accounts or reduced-capability root. The race is timing-dependent, but the KASAN trace shows the lifetime violation is real and reachable in testing.

## 4. Severity interpretation

This behaves above ordinary Moderate because it is not just a warning or NULL dereference. It is a confirmed UAF with a kernel write to freed socket memory. Realistic exploitation evidence currently supports at least local DoS, while privilege escalation remains plausible but not demonstrated. Because the affected surface is BPF plus sockmap and the object is a kernel socket, this should be treated as an Important candidate or at minimum an actionable Moderate requiring manual review.

## 5. One-sentence report phrase

A race between the AF_UNIX BPF iterator sockmap update path and concurrent socket close can leave a stale peer socket pointer and cause a slab use-after-free write in kernel socket memory, allowing at least local DoS and plausibly privilege escalation in capability-delegated BPF environments.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: confirmed UAF, kernel write to freed memory, BPF/sockmap trigger surface, and plausible LPE concern despite race complexity and typical capability restrictions.

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

Patch: bpf, sockmap: Take state lock for af_unix iter [ Upstream
Commit: c6f4015eac2e3cbc3cb7a17539e10bbb5c2049c3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c6f4015eac2e3cbc3cb7a17539e10bbb5c2049c3

Changed files:
  net/unix/af_unix.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=c6f4015eac2e3cbc3cb7a17539e10bbb5c2049c3

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

The original Linux kernel CVE announcement for CVE-2026-53033 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53033

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: 7
  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).