[CVE-2026-74512][MODERATE 7.0] audit: fix potential use-after-free in audit_del_rule()

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

CVE: CVE-2026-74512
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: audit: fix potential use-after-free in audit_del_rule()
Commit: 45bf3df5b32e5a49953e7ceabc55f7dd85380e46
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=45bf3df5b32e5a49953e7ceabc55f7dd85380e46
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74512
Analysis date: Sat, 15 Aug 2026 17:59:51 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in `audit_del_rule()` can free executable audit-rule resources before existing RCU audit-filter readers finish, creating a local use-after-free window that can crash the kernel and may warrant manual review for possible privilege-escalation impact.

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

The original Linux kernel CVE announcement for CVE-2026-74512 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74512

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
======================================================================

CVE-2026-74512	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-672;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'audit rule deletion can create a use after free window because audit_del_rule() may destroy rule exe related resources before the rule is removed from RCU visible filter lists and before existing RCU readers finish. Concurrent audit_filter() or audit_filter_rules() readers can still dereference e rule exe while the underlying fsnotify mark or related object has already been released. For the CVSS the PR:L is used in the paranoid score because a local actor may be able to influence audit activity and race timing in environments with delegated audit management, container root, or a privileged audit management service. The issue is not network reachable and requires local interaction with the audit subsystem. Impact is at least local denial of service via kernel crash and in the worst case may allow confidentiality or integrity impact due to kernel use after free, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 4)	YES	UAF LINUS  INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: **3**
* Paranoid score: **5**
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

**Conservative signals:**

* **Memory corruption, weak/indirect corruption candidate: +1**
  The patch fixes a real UAF window, but no reclaim, overwrite, callback control, type confusion, or arbitrary write primitive is shown.

* **Real lifetime corruption: +1**
  `e->rule.exe` / related fsnotify mark lifetime can end before RCU readers in `audit_filter()` / `audit_filter_rules()` stop using it.

* **Reliable kernel crash / strong DoS: +1**
  A stale dereference in audit filtering can plausibly crash the kernel.

* **Hard or unreliable race / special timing required: -1**
  Triggering requires overlap between audit rule deletion and concurrent audit filtering readers.

* **Privileged audit rule deletion required in typical deployments: -1**
  Deleting audit rules normally requires `CAP_AUDIT_CONTROL` or equivalent privileged audit management. I use `-1`, not full `-2`, because this is a capability-separated security domain rather than necessarily full host root.

* **Broad/default/common subsystem exposure: +1**
  Linux audit is a core security subsystem on many server and enterprise systems, although executable-based audit rules are configuration-dependent.

Conservative total: **3**

**Paranoid additional signals:**

* **Local actor influence on race activity: +1**
  Even if rule deletion is privileged, local users can often generate audit events and increase reader-side activity while a privileged audit management process changes rules.

* **Weak LPE concern due to kernel UAF: +1**
  The primitive is not demonstrated as exploitable, but it is a real RCU lifetime UAF in a privileged kernel security subsystem. This supports manual review sensitivity, not a claim of proven LPE.

Paranoid total before cap: **5**
Race-UAF downgrade cap respected: **paranoid score capped at 5**

## 3. Reachability analysis

The direct delete path is local and normally privileged because audit rule management requires `CAP_AUDIT_CONTROL` or an audit management service. The reader side is easier to stimulate because ordinary local activity can generate audit events, so a reduced-privilege user may help shape timing if a privileged component is concurrently deleting rules.

This is not network reachable by itself. Containers and namespaces matter mainly if audit management is delegated, exposed through a service, or performed by a reduced-capability root process. In ordinary deployments, a fully unprivileged user probably cannot trigger the full bug alone.

Call-site confidence: **medium-high**. The patch and commit explicitly name `audit_filter()` and `audit_filter_rules()` as concurrent RCU readers, but the full reader code is not included in the supplied diff.

## 4. Severity interpretation

This is not an ordinary cleanup bug. It is a real RCU lifetime ordering issue that can create a use-after-free window in the audit subsystem.

Realistic demonstrated impact is closer to **local DoS / Actionable Moderate**, because the patch does not show attacker-controlled reclaim, overwrite, callback dispatch, or type confusion. The paranoid interpretation reaches **ActionableScore 5** because kernel UAFs in security-sensitive subsystems can be underestimated and should not be auto-closed without manual review.

## 5. One-sentence report phrase

A race in `audit_del_rule()` can free executable audit-rule resources before existing RCU audit-filter readers finish, creating a local use-after-free window that can crash the kernel and may warrant manual review for possible privilege-escalation impact.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: this is a real kernel UAF / RCU lifetime bug in the audit security subsystem. No strong exploitation primitive is demonstrated, but the bug class and subsystem make auto-closure unsafe.

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

Patch: audit: fix potential use-after-free in audit_del_rule()
Commit: 45bf3df5b32e5a49953e7ceabc55f7dd85380e46
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=45bf3df5b32e5a49953e7ceabc55f7dd85380e46

Commit description:

`audit_del_rule()` destroys `e->rule.exe` via `audit_remove_mark_rule()`
before unlinking the rule from RCU-visible filter lists and waiting for a
grace period. Concurrent readers in `audit_filter()` and
`audit_filter_rules()` still dereference `e->rule.exe`, while the fsnotify
mark can be freed on an independent lifetime path. This creates a
use-after-free window during rule deletion.

Fix this by unlinking the rule from the RCU-visible lists and invoking
`synchronize_rcu()` before calling `audit_remove_mark_rule()` (and other
rule removal helpers). This ensures that all existing RCU readers have
exited the critical section before any underlying resources are destroyed.

Cc: stable@vger.kernel.org
Fixes: 34d99af ("audit: implement audit by executable")
Reported-by: Vega <vega@nebusec.ai>
Assisted-by: Codex:gpt-5.4
Signed-off-by: Luxiao Xu <rakukuip@gmail.com>
Signed-off-by: Ren Wei <enjou1224z@gmail.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  kernel/auditfilter.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=45bf3df5b32e5a49953e7ceabc55f7dd85380e46

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

The original Linux kernel CVE announcement for CVE-2026-74512 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74512

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:H/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: 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).