[CVE-2026-93144][IMPORTANT] bpf: Reject writes through untrusted BTF pointers [ Upstream

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

CVE: CVE-2026-93144
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: bpf: Reject writes through untrusted BTF pointers [ Upstream
Commit: 19d5566b84ca1af0256d0d0003e1a081580c3ba3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=19d5566b84ca1af0256d0d0003e1a081580c3ba3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93144
Analysis date: Thu, 17 Sep 2026 15:11:31 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
A BPF verifier policy bypass allowed writes through PTR_UNTRUSTED BTF pointers before the common read-only check, creating a plausible kernel memory modification primitive that requires local BPF program loading and should be manually reviewed for privilege escalation impact.

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

The original Linux kernel CVE announcement for CVE-2026-93144 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93144

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.

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

CVE-2026-93144	IMPORTANT	https://www.kernelcve.org/list/?q=CVE-2026-93144 CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-284;CWE-863;CWE-822;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';BEST CVSS score: '7.8';DESCR 'A BPF verifier access control bypass allowed non-read operations through PTR_UNTRUSTED BTF pointers before the common BTF access path enforced the read-only policy. This can let a crafted BPF program write through an untrusted kernel BTF pointer created by helpers such as bpf_rdonly_cast, which is a plausible kernel memory modification primitive rather than a pure crash condition. For the CVSS the PR:L value is used because a local user context with permission to load BPF programs or a delegated BPF capability is needed. The issue is not directly network reachable and requires local BPF program loading. Impact can include kernel memory corruption, denial of service, and potential privilege escalation depending on the reachable BTF object and program type callback behavior.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6)	YES	BPF SIMPLEFIX LINUS  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHERTHAN5	YES	NO	checked

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

ActionableScore=6
ActionableScoreLower=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

## 1. ActionableScore

* Raw conservative score: 5
* Conservative score: 5
* Raw paranoid score: 6
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

No floor or cap changed the score. The BPF privilege-gating cap is respected: conservative remains 5 and paranoid remains 6 because below-host-admin reachability is not fully established, but a verifier-enforced read-only policy bypass with a plausible kernel write primitive is established.

## 2. Signal breakdown

Positive signals:

* +2: Concrete verifier security-policy bypass. `PTR_UNTRUSTED` BTF pointers are intended to be read-only, but program-type `btf_struct_access` callbacks could validate writes before the common BTF path rejected non-read access.
* +2: Strong corruption primitive candidate. The accepted operation is a BPF write through an untrusted kernel BTF pointer, which is materially stronger than a validation-only warning or crash-only condition.
* +1 conservative: Integrity impact is plausible because the bug permits unauthorized modification of kernel state reachable through BTF pointer access rules.
* +1 paranoid: Strong exploitation-leverage concern. The exact reachable BTF objects and callback-specific write permissions are unresolved, so the accepted write primitive needs manual Important-vs-Moderate review.

Negative or non-awarded signals:

* -0: No host-admin-equivalent penalty is applied because host-admin-only reachability is not positively established.
* -0: No local-unprivileged bonus is awarded because ordinary unprivileged BPF program loading is not established.
* -0: No remote reachability bonus. This requires local BPF program loading and is not packet-triggered.
* -0: No UAF, double-release, RCU lifetime, or repeated refcount signal.
* -0: No controlled reclaim or arbitrary kernel read/write is demonstrated.
* -0: No reliable crash-only DoS point is separately awarded because the patch primarily establishes a write-policy bypass, not a demonstrated crash path.
* -0: No extra LPE point is awarded because privilege escalation is plausible but not demonstrated by the supplied evidence.

## 3. Reachability analysis

The trigger is local BPF verifier input: an attacker must be able to load a crafted BPF program using BTF pointer operations and helpers such as `bpf_rdonly_cast()`.

For BPF/XDP privilege separation:

* Load privilege: unresolved. Modern systems often require `CAP_BPF`, `CAP_SYS_ADMIN`, or equivalent policy permission for relevant BPF program loading.
* Attach privilege: not fully established from the patch. Some program types may require additional capabilities.
* Netdevice privilege: not directly established as required by this patch.
* Namespace privilege: unresolved. The supplied evidence does not prove that the complete load and trigger sequence is available in attacker-created namespaces.
* Root-controlled sysctls: unprivileged BPF may be disabled by default, but the exact evaluated product policy is not supplied.

Therefore:

* HostAdminRequired=UNKNOWN, not YES, because host-admin-only reachability is not proven.
* HostAdminRequired=NO is also not justified because ordinary unprivileged reachability is not proven.
* NamespaceScopedPrivilege=UNKNOWN because no complete namespace-scoped trigger chain is established.

There is no direct network trigger, no special hardware requirement, and no race/timing requirement.

## 4. Primitive and severity interpretation

The exact primitive is a BPF verifier access-control bypass that allows non-read access through `PTR_UNTRUSTED` BTF pointers before the common BTF read-only policy is enforced.

This is not a UAF and not a cleanup/destructor lifetime issue. It is also not merely a generic invalid-input rejection. The patch specifically blocks writes that could previously be approved by program-type callbacks despite the pointer being marked untrusted.

PrimitiveClass=CLASS_A because the verifier is a kernel safety boundary and the bug allows an otherwise forbidden write through a restricted kernel pointer class. The established consequence is unauthorized kernel-state modification potential. The speculative consequence is local privilege escalation depending on which BTF object and write callback paths are reachable, but a complete LPE chain is not demonstrated.

ImportantCandidate=YES because BPF verifier policy bypasses involving kernel write capability are security-sensitive and should not be automatically downgraded from patch wording alone.

AutoDowngradeAllowed=NO because automatic closure would risk missing a meaningful verifier-enforced boundary bypass and kernel write primitive.

Likely operational severity: actionable Moderate at minimum, with Strong Important candidate review needed depending on actual BPF privilege policy and reachable program types.

## 5. One-sentence report phrase

A BPF verifier policy bypass allowed writes through PTR_UNTRUSTED BTF pointers before the common read-only check, creating a plausible kernel memory modification primitive that requires local BPF program loading and should be manually reviewed for privilege escalation impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a BPF verifier boundary bypass with a plausible kernel write primitive, not a pure crash or resource leak, and the reachable BTF object set and program-type callback behavior determine whether the issue becomes Important-class.

## 7. Call-site confidence

Call-site confidence: medium

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

Patch: bpf: Reject writes through untrusted BTF pointers [ Upstream
Commit: 19d5566b84ca1af0256d0d0003e1a081580c3ba3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=19d5566b84ca1af0256d0d0003e1a081580c3ba3

Changed files:
  kernel/bpf/verifier.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=19d5566b84ca1af0256d0d0003e1a081580c3ba3

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

The original Linux kernel CVE announcement for CVE-2026-93144 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93144

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:H/I:H/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

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: 5
  Paranoid ActionableScore: 6

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).