[CVE-2026-64028][LOW] tracing: Avoid NULL return from hist_field_name() on truncation [ Upstream

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

CVE: CVE-2026-64028
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: tracing: Avoid NULL return from hist_field_name() on truncation [ Upstream
Commit: e3f5d42cdc2f167719564693675f1eead81378ea
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e3f5d42cdc2f167719564693675f1eead81378ea
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64028
Analysis date: Sun, 19 Jul 2026 16:51:01 -0400
ActionableScore: 2
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like, auto-close candidate
Manual review required: NO

Summary:
A NULL pointer dereference in tracing histogram trigger handling can be triggered by an oversized fully qualified VAR_REF or EXPR name when tracefs histogram controls are writable, causing a local denial of service without evidence of confidentiality impact, integrity impact, or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-64028 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64028

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: LOW
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-2026-64028	LOW	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:N/I:N/A:H';**CWE-476;*CWE-20;CWE-754;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'A NULL pointer dereference in tracing histogram trigger handling can occur because hist_field_name() may return NULL when a fully qualified VAR_REF/EXPR name is truncated. Callers such as strcat and strcmp expect a valid string and can dereference the NULL return, causing a kernel oops or crash. Typical triggering requires write access to tracefs histogram trigger files, which is usually limited to root or CAP_SYS_ADMIN. For the CVSS the PR:L is used for the paranoid score because some deployments may delegate tracing control to a non-root service account. The issue is not network reachable and the impact is denial of service only, with no supported confidentiality or integrity impact.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like, auto-close candidate (with actual score 1)  SKIP CVE-2026-64028 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 5ec1d1e97de134beed3a5b08235a60fc1c51af96 YES  NO NO unknown 	MAYBE	TRACE SIMPLEFIX IMPROVEONLY LINUS  INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=2
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: **0**
* Paranoid score: **2**
* Final recommended bucket: **Ordinary Moderate / Low-like, auto-close candidate**

## 2. Signal breakdown

Conservative scoring:

* **Reliable kernel crash / strong DoS: +1**
  `hist_field_name()` can return `NULL`, and callers pass it to `strcat()` or `strcmp()`, causing a NULL pointer dereference.
* **Requires admin/root/CAP_SYS_ADMIN in typical deployments: -2**
  Triggering requires write access to tracing histogram trigger controls under tracefs, normally restricted to root or CAP_SYS_ADMIN.
* **No generic memory corruption: +0**
  The primitive is a NULL pointer dereference, not UAF, OOB write, double-free, refcount misuse, or type confusion.
* **No confidentiality or integrity impact: +0**
  No read-back, information leak, write primitive, or security-boundary bypass is shown.
* **Not network reachable: +0**
  This is a local tracing control-plane path.

Paranoid scoring:

* **Local unprivileged trigger: +1**
  Only for deployments that delegate tracefs histogram control to a non-root service account or reduced-capability user.
* **Reliable kernel crash / strong DoS: +1**
  The NULL dereference path is direct once the oversized fully qualified VAR_REF/EXPR name reaches truncation.
* **No LPE or memory-corruption bonus: +0**
  A NULL dereference alone does not support privilege escalation.

## 3. Reachability analysis

The bug can be triggered by a local actor able to configure tracing histogram triggers and supply an oversized histogram variable name that reaches the fully qualified VAR_REF/EXPR path. In normal deployments this requires root or CAP_SYS_ADMIN because tracefs trigger files are not writable by ordinary users. Containers do not usually change this unless tracefs access is deliberately exposed or delegated. The path is not network reachable and is not part of packet processing or a default unprivileged API.

Call-site confidence: **high**. The commit identifies concrete dereference callers, including `strcat()` and `strcmp()`.

## 4. Severity interpretation

This behaves like an **ordinary Moderate / Low-like privileged DoS**, not an Important-class kernel vulnerability. The theoretical impact is a kernel oops or crash, but the patch does not show memory corruption, object lifetime misuse, attacker-controlled reclaim, write-after-free, or a plausible LPE primitive. The paranoid score only accounts for environments where tracing control is delegated to a less privileged local actor.

## 5. One-sentence report phrase

A NULL pointer dereference in tracing histogram trigger handling can be triggered by an oversized fully qualified VAR_REF or EXPR name when tracefs histogram controls are writable, causing a local denial of service without evidence of confidentiality impact, integrity impact, or privilege escalation.

## 6. Manual review recommendation

**NO MANUAL CHECK NEEDED**

Reason: this is a local NULL dereference in a privileged tracing control path, with no network exposure and no supported memory-corruption or privilege-escalation primitive.

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

Patch: tracing: Avoid NULL return from hist_field_name() on truncation [ Upstream
Commit: e3f5d42cdc2f167719564693675f1eead81378ea
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e3f5d42cdc2f167719564693675f1eead81378ea

Changed files:
  kernel/trace/trace_events_hist.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=e3f5d42cdc2f167719564693675f1eead81378ea

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

The original Linux kernel CVE announcement for CVE-2026-64028 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64028

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: 0
  Paranoid ActionableScore: 2

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).