[CVE-2026-74258][MODERATE 7.0] bpf: Guard __get_user acesss with access_ok for uprobe_multi data [ Upstream

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

CVE: CVE-2026-74258
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: bpf: Guard __get_user acesss with access_ok for uprobe_multi data [ Upstream
Commit: c6d51ad36490013ee9df94a372d3bf794bd304d1
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c6d51ad36490013ee9df94a372d3bf794bd304d1
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74258
Analysis date: Sat, 15 Aug 2026 10:31:41 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A missing `access_ok()` check before `__get_user()` in the BPF uprobe_multi attach path may allow a local BPF-capable attacker to read data from unvalidated address ranges, with the main realistic impact being kernel information disclosure rather than memory corruption or direct privilege escalation.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74258 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74258

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-74258	MODERATE	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:N/A:L';*CWE-20;CWE-125;*CWE-200;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:N';BEST CVSS score: '6.1';DESCR 'A missing access_ok check in bpf_uprobe_multi_link_attach allowed uoffsets/uref_ctr_offsets/ucookies to be read with __get_user before validating that the supplied ranges are valid userspace addresses. This is a local BPF tracing interface issue rather than a network reachable bug. For the CVSS the PR:L is used in the paranoid score because BPF and tracing permissions may be delegated to a reduced capability local user, service account, or container root in some deployments. The main plausible impact is confidentiality loss because kernel data may be read through an unchecked user pointer path, especially through uprobe_multi cookies that can later be observed by BPF logic. Integrity impact is not strongly supported by the patch context. Availability impact is possible only as a secondary effect of invalid pointer handling or failed attach attempts. Impact should be reviewed manually because this is an unchecked __get_user pattern in a security sensitive BPF path.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	OOB TRACE BPF SIMPLEFIX IMPROVEONLY LINUS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**

## 2. Signal breakdown

Conservative signals:

* Security-boundary bypass with practical sensitive-object access: +2. Missing `access_ok()` before `__get_user()` may allow a privileged BPF caller to make the kernel read from addresses that were not validated as userspace.
* Confidentiality impact plausible: +1. The most plausible impact is kernel memory disclosure through values copied into uprobe multi offsets or cookies.
* Practical exploit chain strongly implied: +1. The `ucookies` path is especially relevant because copied values may later be observable through BPF uprobe logic.
* Broad/common subsystem exposure: +1. BPF tracing is a common kernel facility, although usually privilege-gated.
* Requires admin/root/CAP_BPF/CAP_PERFMON/CAP_SYS_ADMIN in typical deployments: -2. Unprivileged BPF is commonly disabled, and attaching tracing BPF programs usually requires elevated privileges.

Paranoid adjustments:

* Local reduced-privilege trigger: +1. If BPF tracing permissions are delegated to a service account, container root, or reduced-capability user, the attacker may not be equivalent to full host root.
* Privilege penalty reduced from -2 to -1. In delegated-capability deployments, this can bypass a meaningful capability boundary rather than merely giving full root another way to read memory.

Not counted:

* No generic memory corruption signal. The patch shows unchecked reads through `__get_user()`, not UAF, OOB write, double free, type confusion, or arbitrary write.
* No privilege escalation signal. LPE is not supported by the patch.
* No remote/network trigger. This is a local BPF tracing attach path.
* No strong DoS signal. Availability impact is secondary and not the main primitive.

## 3. Reachability analysis

The bug is reachable through `bpf_uprobe_multi_link_attach()` when a caller supplies `uoffsets`, `uref_ctr_offsets`, or `ucookies` arrays that are later read with `__get_user()`. In typical hardened deployments, this path requires privileged BPF or tracing permissions such as `CAP_BPF`, `CAP_PERFMON`, `CAP_SYS_ADMIN`, or root-controlled configuration, so it is not a normal unprivileged local attack surface.

Namespaces and containers matter. If a container root, service account, or delegated BPF-capable process can attach uprobe multi links without full host-root equivalence, the bug becomes more actionable because it may cross the intended kernel/user address validation boundary. The path is not network reachable and requires local code execution plus access to the BPF tracing interface.

Call-site confidence: medium. The changed code and immediate attach path are visible, but full downstream visibility of how all copied values become observable depends on surrounding BPF uprobe_multi behavior.

## 4. Severity interpretation

This behaves more like an actionable Moderate than an ordinary Moderate because it is an unchecked `__get_user()` pattern in a security-sensitive BPF tracing path. The realistic main concern is confidentiality impact from reading data outside validated userspace ranges. Theoretical escalation beyond information disclosure is not supported by the patch.

In conservative product configurations where BPF is root-only, the issue is lower and should not be treated as Important by default. In delegated BPF capability environments, the same bug deserves manual review because the attacker may be less privileged than full host root while still being able to reach the vulnerable attach path.

## 5. One-sentence report phrase

A missing `access_ok()` check before `__get_user()` in the BPF uprobe_multi attach path may allow a local BPF-capable attacker to read data from unvalidated address ranges, with the main realistic impact being kernel information disclosure rather than memory corruption or direct privilege escalation.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is not a DoS-only or simple validation cleanup. It is an unchecked `__get_user()` issue in BPF tracing code, and the final severity depends heavily on whether the target product permits delegated BPF or tracing access to reduced-privilege users.

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

Patch: bpf: Guard __get_user acesss with access_ok for uprobe_multi data [ Upstream
Commit: c6d51ad36490013ee9df94a372d3bf794bd304d1
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c6d51ad36490013ee9df94a372d3bf794bd304d1

Changed files:
  kernel/trace/bpf_trace.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=c6d51ad36490013ee9df94a372d3bf794bd304d1

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

The original Linux kernel CVE announcement for CVE-2026-74258 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74258

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:H/I:N/A:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:L
  The Best / paranoid CVSS score: 6.1

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: 3
  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: NO
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).