[CVE-2026-97936][MODERATE 7.0] tracing: Fix memory corruption from the histogram stacktrace modifier

[CVE-2026-97936][MODERATE 7.0] tracing: Fix memory corruption from the histogram stacktrace modifier

[AL-KERNEL]

CVE: CVE-2026-97936
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: tracing: Fix memory corruption from the histogram stacktrace modifier
Commit: e183b84968d4a6ea476d806ea97668405aa56880
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e183b84968d4a6ea476d806ea97668405aa56880
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97936
Analysis date: Sat, 26 Sep 2026 09:41:13 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-97936 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97936

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-2026-97936	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-97936 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-121;CWE-125;*CWE-20;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:H/A:H';BEST CVSS score: '7.8';DESCR 'A tracing histogram field with the stacktrace modifier can be accepted even when the resolved field does not contain stacktrace data. The kernel then interprets ordinary event data as an offset and entry count and performs an unbounded memcpy into a 31 entry stack array. This produces an out of bounds read followed by a stack buffer overwrite and can corrupt unrelated kernel state or crash the system. For the CVSS the PR:L value in the paranoid score applies when an untrusted local account has delegated write access to tracefs histogram triggers or a tracing instance. Standard systems that restrict this interface to root are closer to PR:H. The issue is not directly network reachable. Impact is at least a local denial of service via kernel memory corruption and in the worst case may allow confidentiality loss integrity compromise or privilege escalation. The confirmed stack overwrite and attacker influenced copy length make manual security review necessary even though reliable privilege escalation is not demonstrated.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)  SKIP CVE-2026-97936 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	KASAN OOB NULLPTR TRACE LINUS  KPANIC INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4	-	-	checked

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

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

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 5
* Raw paranoid score: 3
* Paranoid score: 5
* Applied conservative floor: 3 -> 5 because an attacker-influenced kernel stack overwrite is directly established.
* Applied paranoid floor: 3 -> 5 for the same concrete strong-corruption primitive. No speculative leverage points were added.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Positive signals:

* +2 Strong corruption primitive. An ordinary event field is semantically reinterpreted as a stacktrace descriptor. Its data supplies an offset and unbounded entry count to a `memcpy()` into a fixed 31-entry kernel stack array.
* +1 Reliable kernel crash / strong DoS. The reproducer corrupts unrelated stack state and crashes in timer/rbtree processing. KASAN independently detects the invalid copy.

No double-counting:

* Strong semantic reinterpretation was not separately scored because it is the direct mechanism producing the already-counted OOB write.
* Weak or strong LPE leverage was not separately awarded. The destination is a fixed stack array, but reliable payload shaping, control-flow takeover, and directed kernel writes are not demonstrated.
* No extra Availability point was awarded for the same kernel crash.
* Confidentiality was not awarded because no user-visible disclosure path is established.
* Controlled reclaim, arbitrary kernel read/write, callback control, and demonstrated privilege escalation are absent.
* Remote reachability is not established.
* No privilege penalty was applied because host-admin-only access is not intrinsic to the vulnerable operation and the supplied evidence does not resolve actual tracefs delegation.
* No race penalty applies. The demonstrated trigger is a deterministic configuration and event sequence.

3. Reachability analysis

The attacker must be able to write a histogram trigger under tracefs and then generate the selected event. Default tracefs permissions generally restrict this to host administrators, but tracing instances or relevant files can be delegated to a service account or another local principal. The supplied material does not establish which deployment model applies, so `HostAdminRequired=UNKNOWN` and no privilege bonus or penalty is used.

The operation is controlled by tracefs file permissions rather than an attacker-created user or network namespace. The complete trigger is therefore not inherently namespace-capability scoped. Below-host-admin reachability would normally require prior administrative delegation of the tracing interface.

No special hardware, network exposure, race, or unusual boot mode is required. Kernel tracing and histogram support must be available, and the attacker must have write access to the relevant trigger file.

4. Primitive and severity interpretation

The exact primitive is an attacker-influenced OOB read followed by an unbounded overwrite of a fixed-size kernel stack array. A non-stacktrace field is consumed as though it were a `__data_loc` stacktrace. The resulting offset selects a location in the event record, and the value found there becomes the copy count without source or destination bounds checking.

This is not a UAF, stale-object case, cleanup-only fault, or repeated refcount mutation. It is `CLASS_A` because the patch and reproducer directly establish an attacker-influenced kernel stack overwrite.

The demonstrated consequence is kernel memory corruption and crash. Privilege escalation remains possible in principle because adjacent live stack state is overwritten, but reliable payload control, return-address control, or another stable exploitation mechanism is not established. The issue is therefore an Important candidate requiring exploitation-leverage review rather than a demonstrated LPE.

`AutoDowngradeAllowed=NO` because automatic Moderate closure would discard a concrete strong corruption primitive. The likely operational severity is Actionable Moderate at minimum, with Important classification dependent mainly on actual tracefs delegation and the degree of control over copied event data.

5. One-sentence report phrase

A malformed tracing histogram stacktrace modifier can reinterpret ordinary event data as an unbounded copy descriptor and overwrite a fixed kernel stack array, causing confirmed memory corruption and a kernel crash with unresolved privilege escalation potential.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Review tracefs delegation, affected compiler stack layouts, controllability of the selected event record, and whether the overwrite can reliably influence control data or other security-sensitive stack state.

7. Call-site confidence

Call-site confidence: high

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

Patch: tracing: Fix memory corruption from the histogram stacktrace modifier
Commit: e183b84968d4a6ea476d806ea97668405aa56880
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e183b84968d4a6ea476d806ea97668405aa56880

Commit description:

parse_field() sets HIST_FIELD_FL_STACKTRACE from the ".stacktrace"
modifier before it looks the field name up, and nothing afterwards
checks that the name resolved to a field which holds a stacktrace.
create_hist_field() picks HIST_FIELD_FN_STACK on the strength of the
field pointer alone, which reads a __data_loc word from the record and
follows its low 16 bits as an offset into the same record.
event_hist_trigger() takes the first word there as an entry count and
copies that many longs into a 31 entry array:

	n_entries = *stack;
	memcpy(entries, ++stack, n_entries * sizeof(unsigned long));

Neither end of that copy is bounded, and the count is whatever the event
holds at the offset, so any field will do:

  # cd /sys/kernel/tracing/events/sched/sched_process_fork
  # echo 'hist:keys=parent_pid.stacktrace' > trigger
  # (true)

  BUG: kernel NULL pointer dereference, address: 0000000000000008
  RIP: 0010:rb_insert_color+0x18/0x130
   timerqueue_linked_add+0x7e/0xd0
   enqueue_hrtimer+0x39/0xb0
   __hrtimer_run_queues+0x10f/0x1f0
   </IRQ>
  RIP: 0010:memcpy+0xc/0x30
   event_hist_trigger+0x165/0x690

The timer interrupt landed on the rbtree the copy had already run over.
No debug options are needed for this; KASAN reports the same write as an
out-of-bounds read of 13835058055416381440 bytes.

Documentation/trace/histogram.rst already states the rule, "must be a
long[] type", so enforce it once the name has been resolved. Names which
resolve to no field at all, "hitcount.stacktrace" and the common_*
pseudo-fields, are refused for the same reason: they hold no stacktrace
to read.

Cc: stable@vger.kernel.org
Fixes: cc5fc8b ("tracing/histogram: Add stacktrace type")
Link: https://patch.msgid.link/20260907155045.692664-2-donggeunyoo.kernel@gmail.com
Signed-off-by: Donggeun Yoo <donggeunyoo.kernel@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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=e183b84968d4a6ea476d806ea97668405aa56880

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

The original Linux kernel CVE announcement for CVE-2026-97936 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97936

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:L/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: unknown
  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).