[CVE-2026-74753][MODERATE 7.0] perf: Reject exited events as group leaders [ Upstream

[CVE-2026-74753][MODERATE 7.0] perf: Reject exited events as group leaders [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74753
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: perf: Reject exited events as group leaders [ Upstream
Commit: 7a03413f31c196ab3894f988cdce0bb47b4fec42
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7a03413f31c196ab3894f988cdce0bb47b4fec42
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74753
Analysis date: Wed, 26 Aug 2026 13:55:44 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A local perf_event_open lifetime bug can allow an EXIT state remove_on_exec event to be reused as a group leader, leaving a sibling with a dangling group_leader pointer to a freed perf_event and creating a UAF candidate with crash impact and possible higher risk.

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

The original Linux kernel CVE announcement for CVE-2026-74753 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74753

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-2026-74753	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A use-after-free candidate exists in perf event grouping because an event moved to EXIT by remove_on_exec could still be accepted as a group leader while its file descriptor remains open. A new sibling can then keep a group_leader pointer to a freed perf_event after the leader is closed, which can lead to kernel memory corruption or crash. For the CVSS the PR:L is used because triggering requires local code execution and permission to create perf events through perf_event_open, but it does not necessarily require full administrative privileges on systems where perf is available to users. The issue is not network reachable and is triggered through a local kernel syscall interface. Impact is at least local denial of service via kernel crash and in the paranoid case may include confidentiality and integrity impact due to the dangling kernel pointer and possible use-after-free.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)  SKIP CVE-2026-74753 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	DANGER INIT UAF HARDWARE LINUS TEST  INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	-	-	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

Conservative score: 4
Paranoid score: 5
Final recommended bucket: **Actionable Moderate at minimum**

## 2. Signal breakdown

Triggered signals:

- Local unprivileged trigger: +1
  The path is reachable through `perf_event_open()` by a local process when perf access is allowed by system policy.

- Memory corruption, weak/indirect corruption candidate: +1
  The patch describes a sibling retaining `group_leader` pointing to a freed `perf_event`. This is a UAF candidate, but no controlled reclaim, overwrite, callback control, or arbitrary write primitive is shown.

- Real lifetime corruption: +1
  The bug is a stale pointer after the group leader is detached, closed, and freed.

- Reliable kernel crash / strong DoS: +1
  A dangling pointer in perf core can realistically lead to kernel crash or corrupted perf state.

- Broad/default/common subsystem: +1 in paranoid score
  perf is a common kernel subsystem, although practical reachability depends on `perf_event_paranoid` and distribution policy.

Subtracted signals:

- Hard or unreliable race / special timing required: -1 in conservative score
  The issue depends on an exec/remove_on_exec lifetime window and group attachment timing.

## 3. Reachability analysis

The bug is local, not network reachable. An attacker needs local code execution and the ability to call `perf_event_open()` with a still-open remove-on-exec event used as a group leader. On systems where unprivileged perf is restricted by `perf_event_paranoid`, practical reachability may require elevated permissions or a more permissive configuration. Containers and delegated environments matter because a reduced-capability service or container context with perf access may still be meaningfully less privileged than full host root.

Call-site confidence: high. The patch is in `SYSCALL_DEFINE5(perf_event_open)` and explicitly revalidates `group_leader->state` under `ctx::mutex`, so the relevant attachment path is visible.

## 4. Severity interpretation

This is not an ordinary DoS-only cleanup. The commit explicitly describes a retained pointer to a freed `perf_event`, which makes it a real lifetime bug and a UAF candidate in a core kernel subsystem. However, the provided patch does not demonstrate attacker-controlled reclaim, controlled overwrite, callback dispatch, refcount takeover, or arbitrary read/write. Therefore the conservative interpretation is borderline/manual-review Moderate, while the paranoid interpretation is Actionable Moderate at minimum rather than a fully confirmed Important.

## 5. One-sentence report phrase

A local perf_event_open lifetime bug can allow an EXIT state remove_on_exec event to be reused as a group leader, leaving a sibling with a dangling group_leader pointer to a freed perf_event and creating a UAF candidate with crash impact and possible higher risk.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.
YES REQUIRES MANUAL CHECK.

Reason: the bug is a kernel lifetime/UAF candidate in perf core. Even though no strong exploitation primitive is demonstrated, the freed `perf_event` pointer surviving in a sibling object is enough to require manual security review rather than autoclosing as ordinary Moderate.

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

Patch: perf: Reject exited events as group leaders [ Upstream
Commit: 7a03413f31c196ab3894f988cdce0bb47b4fec42
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7a03413f31c196ab3894f988cdce0bb47b4fec42

Changed files:
  kernel/events/core.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=7a03413f31c196ab3894f988cdce0bb47b4fec42

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

The original Linux kernel CVE announcement for CVE-2026-74753 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74753

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:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

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: 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).