[CVE-2026-53110][MODERATE 7.0] s390/bpf: Zero-extend bpf prog return values and kfunc arguments [ Upstream

[CVE-2026-53110][MODERATE 7.0] s390/bpf: Zero-extend bpf prog return values and kfunc arguments [ Upstream

[AL-KERNEL]

CVE: CVE-2026-53110
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: s390/bpf: Zero-extend bpf prog return values and kfunc arguments [ Upstream
Commit: edc90a12073b9a530064a99945c183dde120cb99
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=edc90a12073b9a530064a99945c183dde120cb99
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53110
Analysis date: Wed, 24 Jun 2026 13:46:22 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A s390 BPF JIT ABI mismatch caused unsigned BPF trampoline return values and kfunc arguments to be sign-extended instead of zero-extended, allowing local BPF-capable users to pass incorrect kernel-side values with possible integrity or availability impact.

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

The original Linux kernel CVE announcement for CVE-2026-53110 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53110

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 7.0
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-2026-53110	MODERATE	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:L/I:L/A:H';CWE-681;CWE-704;CWE-682;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '5.8';DESCR 'A s390 BPF JIT ABI mismatch can occur because unsigned BPF trampoline return values and kfunc arguments were sign extended instead of zero extended. Values of 1, 2, or 4 byte unsigned types with the top bit set may therefore reach kernel kfuncs or trampoline return handling with incorrect upper register bits. This is not directly network reachable and requires local ability to load or attach a relevant BPF program on s390. For the CVSS the PR:L is used because the practical trigger requires a local user or service account with BPF related permissions rather than remote packet reachability. Impact is primarily incorrect kernel side semantics with possible integrity impact or denial of service if the wrong value is used as a size, index, flag, or return code. For the paranoid score, the highest still defensible interpretation is C:L/I:L/A:H because the bug affects BPF JIT and kfunc call semantics, but the patch does not show a direct UAF, OOB write, or arbitrary write primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	INIT BPF HARDWARE LINUS  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK	YES	NO	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: **4**
* Paranoid score: **5**
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* **Local BPF-capable trigger: +1**
  Trigger requires local ability to load or attach a relevant BPF program using the s390 BPF JIT trampoline or kfunc path. This is not remotely reachable.
* **Local high-control kernel data-plane API: +1**
  BPF is a high-control kernel interface, and this bug affects generated JIT trampoline code and kfunc argument passing.
* **Weak or indirect corruption candidate: +1**
  The primitive is not UAF, OOB write, double-free, or arbitrary write. However, unsigned 1, 2, or 4 byte values may reach kernel kfuncs or trampoline return handling with incorrect upper bits.
* **Integrity impact plausible: +1**
  Wrongly sign-extended unsigned values may affect kernel-side decisions if used as flags, return codes, indexes, or sizes.
* **Availability impact plausible: +1**
  A bad argument value may plausibly trigger incorrect behavior or crash in sensitive kfunc paths, although the patch does not demonstrate a reliable crash.
* **s390-specific exposure: -1**
  The issue is architecture-specific to s390 BPF JIT behavior, reducing broad deployment exposure compared with generic BPF core bugs.

Paranoid delta:

* **Paranoid semantic impact elevation: +1**
  Because this is in BPF JIT trampoline and kfunc ABI handling, incorrect values can cross a sensitive kernel boundary. This justifies Actionable Moderate handling, but not Important-class scoring without a concrete memory corruption primitive.

Not applied:

* **Remote reachable: +0**
  No network-triggerable path is shown.
* **Strong LPE plausibility: +0**
  No attacker-controlled reclaim, arbitrary write, callback overwrite, type confusion, or refcount takeover is shown.
* **Strong generic memory corruption: +0**
  The patch fixes sign vs zero extension, not a direct memory lifetime or bounds violation.

## 3. Reachability analysis

The bug is reachable by a local actor that can load or attach BPF programs exercising s390 BPF trampolines or kfunc calls. In typical hardened deployments, BPF loading requires capabilities such as CAP_BPF, CAP_PERFMON, or CAP_SYS_ADMIN, or a privileged service that manages BPF programs. If unprivileged BPF is enabled or BPF access is delegated to containers or service accounts, the practical privilege requirement becomes lower.

The path is not network reachable by itself. It is also not a generic multi-architecture BPF bug because the incorrect ABI handling is specific to s390 JIT code generation.

## 4. Severity interpretation

This behaves more like an **Actionable Moderate** than an ordinary Moderate because the affected code is BPF JIT trampoline and kfunc ABI handling, where incorrect argument or return-value extension may influence kernel-side semantics. However, the patch does not show a direct UAF, OOB write, arbitrary write, function-pointer overwrite, or demonstrated privilege-escalation primitive.

Theoretical risk includes incorrect kernel decisions or crashes if malformed unsigned values are interpreted as signed-extended values in sensitive kfunc paths. Realistic exploitation evidence is limited, so this should not be treated as a Strong Important candidate without additional proof.

## 5. One-sentence report phrase

A s390 BPF JIT ABI mismatch caused unsigned BPF trampoline return values and kfunc arguments to be sign-extended instead of zero-extended, allowing local BPF-capable users to pass incorrect kernel-side values with possible integrity or availability impact.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: BPF JIT and kfunc ABI bugs are security-sensitive and may produce non-obvious kernel-side semantic corruption, but the available patch does not prove a concrete memory corruption or LPE primitive. Manual review should verify whether any affected kfunc or trampoline return path can turn the wrong upper bits into a stronger primitive.

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

Patch: s390/bpf: Zero-extend bpf prog return values and kfunc arguments [ Upstream
Commit: edc90a12073b9a530064a99945c183dde120cb99
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=edc90a12073b9a530064a99945c183dde120cb99

Changed files:
  arch/s390/net/bpf_jit_comp.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=edc90a12073b9a530064a99945c183dde120cb99

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

The original Linux kernel CVE announcement for CVE-2026-53110 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53110

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:N/I:L/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 4
  Paranoid ActionableScore: 5

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).