[CVE-2026-90159][MODERATE REGULAR] bpf: Disallow bpf_{g,s}etsockopt() in cgroup UNIX getname hooks [ Upstream

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

CVE: CVE-2026-90159
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: bpf: Disallow bpf_{g,s}etsockopt() in cgroup UNIX getname hooks [ Upstream
Commit: 61769b9c882a964af3a6ebd9a8e43615f8713234
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=61769b9c882a964af3a6ebd9a8e43615f8713234
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90159
Analysis date: Thu, 17 Sep 2026 23:37:22 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-90159 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90159

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: NO

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

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

CVE-2026-90159	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-90159 CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-667;CWE-362;CWE-754;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'The cgroup UNIX getpeername and getsockname hooks allowed BPF programs to call bpf_setsockopt or bpf_getsockopt even though these hooks run without holding the socket lock expected by the helpers. A locally attached BPF program can therefore call a helper in an invalid locking context and trigger the sock_owned_by_me warning. On systems configured with panic_on_warn this can cause a kernel panic and denial of service. Without that configuration the confirmed result is a kernel warning and possible log or service disruption. For the CVSS the PR:L value is used for the paranoid score because delegated cgroup BPF administration, container root, or a restricted service account may be sufficient even when full host root access is unavailable. The normal deployment usually requires elevated BPF or network capabilities, so the base score uses PR:H. The issue is not directly network reachable because an attacker must first load and attach a BPF program to an affected cgroup UNIX getname hook. No concrete UAF, OOB access, information leak, or arbitrary write primitive is demonstrated, so confidentiality and integrity remain unaffected in both scores.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)  SKIP CVE-2026-90159 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	REMOTE BPF  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

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

ActionableScore=1
ActionableScoreLower=0
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 0.
* Conservative score: 0.
* Raw paranoid score: 1.
* Paranoid score: 1.
* No floor or cap changed either score.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

Conservative signals:

* +0 WARN or invalid locking context. The established result is `sock_owned_by_me()` warning when a BPF helper is invoked without the expected socket lock.
* +0 crash. The patch does not establish a fatal fault under the normal WARN continuation behavior.
* +0 privilege penalty. The complete BPF load and attachment privilege boundary is unresolved, so host-admin privilege is not assumed.
* +0 timing penalty. No narrow or unreliable race is required to trigger the warning.

Paranoid signals:

* +1 reliable kernel crash or strong DoS. A deliberate warning can panic the kernel when `panic_on_warn` is enabled, although this is configuration-dependent.

Important non-awarded signals:

* No UAF, stale lifetime use, double release, refcount mutation, OOB access, arbitrary write, controlled reclaim, or information disclosure is established.
* No weak or strong corruption point is awarded merely because `bpf_setsockopt()` can modify socket state without the expected lock. The supplied evidence establishes the lock-contract violation and warning, but not a concrete corrupted field or useful concurrent mutation.
* No additional availability point is awarded because a panic caused by the warning is the same DoS consequence.
* No local-unprivileged point is awarded because ordinary-user ability to complete BPF program loading and cgroup attachment is not established.
* No remote-reachability point is awarded. UNIX socket operations do not remove the prerequisite of a locally loaded and attached BPF program.
* No race penalty is applied merely because missing locking could permit concurrency.
* No BPF UAF floor applies because there is no UAF.

Arithmetic:

* Conservative: 0 = 0.
* Paranoid: +1 conditional fatal warning = 1.

3. Reachability analysis

The attacker must load a BPF program that calls `bpf_setsockopt()` or `bpf_getsockopt()`, attach it to `BPF_CGROUP_UNIX_GETPEERNAME` or `BPF_CGROUP_UNIX_GETSOCKNAME`, and trigger the corresponding UNIX socket name operation.

The supplied patch does not resolve the complete capability chain for program loading, cgroup attachment, and trigger execution. BPF loading commonly requires BPF-related capabilities or privileged policy, but that does not positively establish host-admin equivalence for every affected deployment. Therefore `HostAdminRequired=UNKNOWN`.

The presence of cgroups and UNIX sockets does not establish that all operations can be completed with attacker-obtainable namespace capabilities. Therefore `NamespaceScopedPrivilege=UNKNOWN`. A delegated BPF management service could expose the path below full host administration, but such delegation is not established here.

There is no direct network trigger. No special hardware is required. The warning appears deterministic once an eligible program is attached and invokes the helper, so no hard-race penalty applies. Fatal impact additionally depends on `panic_on_warn` or equivalent warning-to-panic policy.

4. Primitive and severity interpretation

The exact established primitive is invocation of full-socket BPF option helpers from hooks that do not hold the socket lock expected by those helpers. The demonstrated consequence is a lock-ownership warning.

This is not an active-object UAF, fixed stale-storage access, repeated release, or authorization bypass. No first lifetime-ending operation or second lifetime mutation exists. The issue is therefore `CLASS_C`, representing invalid-state and possible DoS behavior rather than an independently useful corruption primitive.

A kernel panic is technically defensible on systems configured to panic on warnings. Broader socket-state corruption is speculative because the supplied context does not identify a concrete unsafe mutation, stale object, corrupted target, or subsequent exploitation sink.

`ImportantCandidate=NO` because no Important-preserving primitive or meaningful unresolved lifetime corruption is established. `AutoDowngradeAllowed=YES` because the confirmed behavior is warning or configuration-dependent DoS, with no unresolved UAF, controlled corruption, or security-boundary bypass. Operationally this is an ordinary Moderate issue, potentially more disruptive on hosts using `panic_on_warn`.

5. One-sentence report phrase

The cgroup UNIX getname hooks allowed BPF socket option helpers to run without their required socket lock, causing a kernel warning and a possible local denial of service when warnings are configured as fatal.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Review the concrete `_bpf_setsockopt()` option paths to confirm that unlocked execution cannot mutate socket state in a way that produces corruption beyond the documented warning.

7. Call-site confidence

Call-site confidence: medium

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

Patch: bpf: Disallow bpf_{g,s}etsockopt() in cgroup UNIX getname hooks [ Upstream
Commit: 61769b9c882a964af3a6ebd9a8e43615f8713234
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=61769b9c882a964af3a6ebd9a8e43615f8713234

Changed files:
  net/core/filter.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=61769b9c882a964af3a6ebd9a8e43615f8713234

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

The original Linux kernel CVE announcement for CVE-2026-90159 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90159

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:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: 0
  Paranoid ActionableScore: 1

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).