[CVE-2026-74391][MODERATE 7.0] tracing: Bound synthetic-field strings with seq_buf [ Upstream

[CVE-2026-74391][MODERATE 7.0] tracing: Bound synthetic-field strings with seq_buf [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74391
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: tracing: Bound synthetic-field strings with seq_buf [ Upstream
Commit: 0c584c27f6649a93ec12061cc779a4bd8f7c1434
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0c584c27f6649a93ec12061cc779a4bd8f7c1434
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74391
Analysis date: Sat, 15 Aug 2026 05:38:05 -0400
ActionableScore: 8
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A kernel heap out-of-bounds write in tracing synthetic field handling can be triggered through oversized hist trigger strings, causing at least local DoS and potentially privilege escalation when tracing access is delegated.

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

The original Linux kernel CVE announcement for CVE-2026-74391 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74391

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-2026-74391	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:H/A:H';*CWE-787;CWE-122;CWE-120;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H';BEST CVSS score: '7.8';DESCR 'Tracing synthetic field helpers build synthetic variable names and generated hist commands in fixed MAX_FILTER_STR_VAL heap buffers. The old code used raw strcat on attacker influenced field names, key lists, and saved filters, so an overlong configuration can write past the end of the staging buffer in kernel memory. This is a local tracefs control plane issue rather than a packet or remote network path. In typical deployments only administrators can configure hist triggers through tracefs. For the CVSS the PR:L is used for the paranoid score because some systems may delegate tracing access to non root users, service accounts, or container root with tracing related capabilities. Impact is at least denial of service via kernel memory corruption and may include privilege escalation if the heap overflow can be shaped reliably.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 6)	YES	INIT TRACE  KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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

ActionableScore=8
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 8
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Memory corruption, strong corruption primitive: +2
  Raw `strcat()` appends attacker-influenced tracing strings into fixed `MAX_FILTER_STR_VAL` heap buffers, creating a kernel heap OOB write risk.
* Reliable kernel crash / strong DoS: +1
  Heap overflow in kernel tracing configuration can realistically crash the kernel.
* Weak LPE concern: +1
  The overflow is attacker-influenced, but no concrete reclaim, target object, or exploit primitive is shown in the patch.
* Requires admin/root/CAP_* in typical deployments: -2
  Hist trigger configuration through tracefs is normally restricted to root or privileged tracing administrators.
* Confidentiality impact plausible: +1
  Heap corruption can plausibly affect adjacent kernel objects, though no info leak primitive is demonstrated.
* Integrity impact plausible: +1
  Kernel heap overwrite can plausibly corrupt kernel state.

Conservative total: 4.

Paranoid signals:

* Local low-privilege trigger: +1
  Some systems delegate tracing access to non-root users, tracing groups, service accounts, or container-root-like roles.
* Privilege escalation plausible: +2
  A controllable heap overflow in kernel memory is a classic LPE-relevant primitive if heap layout can be shaped.
* Memory corruption, strong corruption primitive: +2
  This is an OOB heap write, not merely validation or DoS-only behavior.
* Reliable kernel crash / strong DoS: +1
  Even without LPE, a kernel crash is realistic.
* Confidentiality impact plausible: +1
  Kernel heap corruption can plausibly expose or influence sensitive kernel data.
* Integrity impact plausible: +1
  Kernel heap corruption can plausibly modify kernel control or data objects.

Paranoid total: 8.

## 3. Reachability analysis

The bug is local and reachable through tracing hist trigger configuration, not through a remote network path. In default hardened deployments, access to tracefs histogram trigger configuration is usually root-only or requires administrative capabilities, so the conservative score applies a privilege penalty. However, practical deployments sometimes delegate tracing access to non-root diagnostic users, service accounts, or partially privileged container/root contexts, which makes PR:L plausible for triage. The affected tracing subsystem is commonly built and deployed, but the vulnerable path requires explicit tracing configuration activity.

Call-site confidence: high. The patch directly shows both vulnerable string construction sites and the bounded replacement behavior.

## 4. Severity interpretation

This is not an ordinary Moderate resource leak or warning-only issue. The patch fixes unbounded string concatenation into fixed-size kernel heap buffers, which is a concrete OOB write primitive. Realistic exploitation as LPE is not demonstrated by the patch, but the bug class and attacker-influenced payload justify manual review and a high paranoid score. Conservative handling is borderline because the typical trigger requires privileged tracing access, but delegated tracing deployments make this an actionable issue.

## 5. One-sentence report phrase

A kernel heap out-of-bounds write in tracing synthetic field handling can be triggered through oversized hist trigger strings, causing at least local DoS and potentially privilege escalation when tracing access is delegated.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.
YES REQUIRES MANUAL CHECK because this is attacker-influenced kernel heap memory corruption in a configurable tracing path, with plausible LPE relevance under delegated tracing access.

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

Patch: tracing: Bound synthetic-field strings with seq_buf [ Upstream
Commit: 0c584c27f6649a93ec12061cc779a4bd8f7c1434
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0c584c27f6649a93ec12061cc779a4bd8f7c1434

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=0c584c27f6649a93ec12061cc779a4bd8f7c1434

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

The original Linux kernel CVE announcement for CVE-2026-74391 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74391

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: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: 4
  Paranoid ActionableScore: 8

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).