[CVE-2026-53035][MODERATE REGULAR] bpf, sockmap: Fix af_unix iter deadlock [ Upstream

[CVE-2026-53035][MODERATE REGULAR] bpf, sockmap: Fix af_unix iter deadlock [ Upstream

[AL-KERNEL]

CVE: CVE-2026-53035
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: bpf, sockmap: Fix af_unix iter deadlock [ Upstream
Commit: bd3592129f24243713673a07225cf1f15a9bb835
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bd3592129f24243713673a07225cf1f15a9bb835
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53035
Analysis date: Fri, 26 Jun 2026 15:25:58 -0400
ActionableScore: 4
ActionableScore lower bound: 1
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
A local BPF iterator over AF_UNIX sockets can deadlock the kernel when an iterator program updates a sockmap while the same socket lock is already held, causing a local denial of service without evidence of memory corruption or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-53035 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53035

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 REGULAR
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-2026-53035	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:N/I:N/A:H';CWE-667;*CWE-833;**CWE-400;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'The AF_UNIX BPF iterator can deadlock because bpf_iter_unix_seq_show may run an iterator program while lock_sock_fast has taken the fast path and still holds the socket spinlock. If the iterator program updates a sockmap, sock_map_update_elem tries to take the same AF_UNIX socket lock again and can spin forever. For the CVSS the PR:L is used in the paranoid score because delegated BPF or network administration capability may be available to a non-root local service account, although typical systems require higher privileges to load this iterator program. The issue is not network reachable and is triggered through local BPF iterator and sockmap operations. Impact is denial of service due to a kernel deadlock or soft lockup, with no concrete evidence of information disclosure or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 3) 	MAYBE	REMOTE LOCK DEADLOCK NULLPTR BPF HARDWARE TEST  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=4
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 4
* Final recommended bucket: **Borderline, manual review recommended**::

## 2. Signal breakdown

Conservative signals:

* Reliable kernel crash / strong DoS: +1
  The patch fixes a recursive locking scenario where `bpf_iter_unix_seq_show()` can run a BPF iterator program while the AF_UNIX socket spinlock is already held, and `sock_map_update_elem()` then tries to acquire the same lock again.
* Local unprivileged high-control kernel data-plane API: +1
  BPF plus sockmap is a high-control kernel API, but in typical deployments loading and running this iterator program requires elevated BPF related privileges.
* Requires admin/root/CAP_* in typical deployments: -2
  Practical triggering normally requires capability-gated BPF iterator and sockmap operations, commonly CAP_BPF, CAP_NET_ADMIN, CAP_PERFMON, or CAP_SYS_ADMIN depending on kernel and distro policy.
* Availability impact realistic: +1
  The impact is a persistent local deadlock or soft lockup condition, not just a benign warning.

Paranoid signals:

* Reliable kernel crash / strong DoS: +1
* Availability impact realistic: +1
* Local high-control kernel data-plane API: +1
* Broad/common subsystem exposure: +1
  AF_UNIX, BPF, and sockmap infrastructure are common kernel facilities, even if this exact iterator path is not default-exposed to all users.
* No full privilege penalty in paranoid interpretation: +0
  If BPF or network administration capability is delegated to a non-root service account, container manager, or reduced-capability root context, this is not equivalent to full host root.

Not counted:

* Remote reachable: +0
  No network packet path directly triggers the issue.
* Generic memory corruption: +0
  The patch shows recursive locking and deadlock, not UAF, double-free, OOB write, type confusion, or arbitrary write.
* Privilege escalation plausible: +0
  No credible LPE primitive is visible from the diff or commit context.
* Confidentiality or integrity impact: +0
  No information leak, object overwrite, policy bypass, or sensitive object access primitive is shown.

## 3. Reachability analysis

The bug is locally triggered through BPF iterator execution over AF_UNIX sockets combined with a sockmap update from the iterator program. In typical production kernels, this requires privileged BPF functionality and likely CAP_BPF plus related capabilities, or CAP_SYS_ADMIN on older configurations.

Namespaces and containers may matter if a container or service is delegated BPF or network administration capabilities. In that case the practical privilege level can be closer to PR:L than PR:H, because the attacker may not have full host-root authority but can still exercise the vulnerable BPF and sockmap paths.

The affected path is not remotely reachable by ordinary network traffic. It is also not a default unprivileged interface on most hardened distributions. Realistic exploitation is a local DoS by a user or service with enough BPF capability to load and run the iterator program.

## 4. Severity interpretation

This behaves more like a borderline Moderate local DoS than an Important-class vulnerability. The conservative interpretation is low because the trigger is capability-gated and the demonstrated impact is deadlock only.

The paranoid interpretation reaches manual-review territory because BPF and sockmap are high-control kernel interfaces, and delegated BPF capabilities can exist in real service or containerized environments. However, there is no evidence of memory corruption, privilege escalation, information disclosure, or cross-boundary object access. The realistic impact remains availability loss through a local kernel deadlock or soft lockup.

## 5. One-sentence report phrase

A local BPF iterator over AF_UNIX sockets can deadlock the kernel when an iterator program updates a sockmap while the same socket lock is already held, causing a local denial of service without evidence of memory corruption or privilege escalation.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because the issue is BPF reachable and can cause a persistent kernel deadlock, and because delegated BPF capability environments may reduce the practical privilege requirement. It does not currently look like an Important-class issue because the patch supports DoS only and does not show a memory corruption or privilege escalation primitive.

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

Patch: bpf, sockmap: Fix af_unix iter deadlock [ Upstream
Commit: bd3592129f24243713673a07225cf1f15a9bb835
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bd3592129f24243713673a07225cf1f15a9bb835

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=bd3592129f24243713673a07225cf1f15a9bb835

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

The original Linux kernel CVE announcement for CVE-2026-53035 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53035

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:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  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: 1
  Paranoid ActionableScore: 4

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 REGULAR

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).