[CVE-2026-74288][MODERATE REGULAR] net: fib_rules: Don't dump dying fib_rule in fib_rules_dump(). [ Upstream

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

CVE: CVE-2026-74288
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net: fib_rules: Don't dump dying fib_rule in fib_rules_dump(). [ Upstream
Commit: 0f929b59f4cd0e05bb1ecefe12b77e85911d4be2
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0f929b59f4cd0e05bb1ecefe12b77e85911d4be2
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74288
Analysis date: Sun, 16 Aug 2026 06:21:18 -0400
ActionableScore: 4
ActionableScore lower bound: 1
Actionable bucket: Borderline manual review recommended / Actionable Moderate candidate in paranoid interpretation
Manual review required: YES

Summary:
`fib_rules_dump() could pass a dying RCU protected fib_rule to FIB notifier callbacks, causing refcount misuse and a possible weak UAF candidate under a local control-plane race, with typical triggering requiring network administration privileges.`

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

The original Linux kernel CVE announcement for CVE-2026-74288 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74288

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 REGULAR
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-2026-74288	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:L/I:L/A:H';CWE-362;*CWE-416;CWE-911;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'fib_rules_dump can expose a dying fib_rule to a FIB notifier while walking the rules list under RCU. A notifier callback such as rocker_router_fib_event may then try to take a reference with fib_rule_get() after the object refcount has reached zero, which is a refcount lifetime violation and a possible use-after-free candidate. For the CVSS the PR:L value is used for the paranoid score because a reduced capability root, container root, service account, or delegated CAP_NET_ADMIN context may be enough in some deployments to manipulate rules or related network objects. The issue is not directly network reachable and requires a local control plane race rather than packet traffic. Impact is at least denial of service via warning or kernel crash, and in worst case may allow limited confidentiality or integrity impact due to memory lifetime corruption and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / Actionable Moderate candidate in paranoid interpretation (with actual score 3)	YES	REMOTE SIMPLEFIX  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=4
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 4
* Final recommended bucket: **Borderline manual review recommended / Actionable Moderate candidate in paranoid interpretation**::

## 2. Signal breakdown

Paranoid score signals:

* Weak/indirect corruption candidate: +1
  `fib_rules_dump()` can expose a dying `fib_rule` to notifier callbacks while walking the RCU list. This is a refcount lifetime violation, but no controlled reclaim, overwrite, type confusion, or attacker-controlled replacement is shown.

* Real lifetime corruption: +1
  The patch changes plain `refcount_inc()` behavior to `refcount_inc_not_zero()` through `fib_rule_get_safe()`, which directly indicates a dying-object/refcount lifetime issue.

* Weak LPE concern: +1
  This is not a strong LPE primitive, but notifier callback use of an object whose refcount reached zero is enough to keep a weak manual-review concern.

* Broad/default/common subsystem: +1
  FIB rules are part of core networking infrastructure, though the affected path is control-plane notifier dumping rather than packet RX/TX.

* Hard or unreliable race / special timing required: -1
  The issue requires overlap between rule teardown and FIB notifier dump.

* Privilege penalty: 0 in paranoid interpretation
  Typical triggering likely needs `CAP_NET_ADMIN` or equivalent control over network rule/device state, but delegated netadmin, container root, or service contexts may reduce the practical privilege barrier.

Conservative score signals:

* Weak/indirect corruption candidate: +1
* Real lifetime corruption: +1
* Hard race: -1
* Requires CAP_NET_ADMIN or privileged network control in typical deployments: -2
* Broad networking subsystem: +1

Net conservative result: 1.

## 3. Reachability analysis

The issue is not directly network reachable and is not triggered by ordinary packet traffic. A realistic trigger requires local control-plane activity involving FIB rules and notifier registration or device paths such as `rocker_router_fib_event()`. In typical deployments this requires administrative networking privileges, usually `CAP_NET_ADMIN` or root-level device management. Namespaces and containers matter because delegated `CAP_NET_ADMIN`, container root, or a service account managing network configuration may make the practical privilege requirement closer to PR:L than PR:H. The path is in core networking code, but the vulnerable operation is a narrow RCU/refcount race during dumping of rules to notifiers.

Call-site confidence: high. The affected call site in `fib_rules_dump()` and the notifier call are visible in the patch.

## 4. Severity interpretation

This behaves more like a borderline manual-review Moderate than a clear Important issue. The theoretical concern is memory lifetime corruption because a dying `fib_rule` can be handed to a notifier callback and referenced after its refcount reached zero. The realistic evidence is weaker: the commit describes a refcount warning and fixes it by skipping zero-refcount rules, but it does not show attacker-controlled reclaim, write-after-free, object replacement, type confusion, or arbitrary read/write. Therefore the conservative interpretation is low priority, while the paranoid interpretation justifies manual review because refcount lifetime bugs in core networking callbacks can be underestimated.

## 5. One-sentence report phrase

`fib_rules_dump() could pass a dying RCU protected fib_rule to FIB notifier callbacks, causing refcount misuse and a possible weak UAF candidate under a local control-plane race, with typical triggering requiring network administration privileges.`

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED.

Reason: this is not a strong Important candidate from the patch alone, but it is a real refcount/RCU lifetime issue in core networking notifier code, and the practical privilege boundary may be lower in delegated `CAP_NET_ADMIN` or containerized environments.

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

Patch: net: fib_rules: Don't dump dying fib_rule in fib_rules_dump(). [ Upstream
Commit: 0f929b59f4cd0e05bb1ecefe12b77e85911d4be2
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0f929b59f4cd0e05bb1ecefe12b77e85911d4be2

Changed files:
  include/net/fib_rules.h
  net/core/fib_rules.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=0f929b59f4cd0e05bb1ecefe12b77e85911d4be2

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

The original Linux kernel CVE announcement for CVE-2026-74288 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74288

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:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 1
  Paranoid ActionableScore: 4

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 REGULAR

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).