[CVE-2026-74726][MODERATE REGULAR] bonding: alb: re-check primary_is_promisc under RTNL in bond_alb_monitor [ Upstream

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

CVE: CVE-2026-74726
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: bonding: alb: re-check primary_is_promisc under RTNL in bond_alb_monitor [ Upstream
Commit: f7668762bf5fd6db9397de5c0514407489d9d815
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f7668762bf5fd6db9397de5c0514407489d9d815
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74726
Analysis date: Sat, 22 Aug 2026 16:26:53 -0400
ActionableScore: 4
ActionableScore lower bound: 2
Actionable bucket: Borderline manual review recommended / Actionable Moderate in delegated CAP_NET_ADMIN deployments
Manual review required: YES

Summary:
A race in `bond_alb_monitor()` can use stale `primary_is_promisc` state after RTNL acquisition, causing either a NULL dereference kernel panic or an incorrect promiscuity counter decrement that may leave a bonding slave pinned in promiscuous mode.

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

The original Linux kernel CVE announcement for CVE-2026-74726 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74726

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-2026-74726	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	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-476;CWE-667;CWE-682;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:L/A:H';BEST CVSS score: '5.8';DESCR 'A race in bond_alb_monitor can occur because primary_is_promisc is checked before RTNL is acquired while the active slave can change under RTNL. If the slave is removed without failover, curr_active_slave can become NULL and the monitor can dereference it, causing a kernel panic. If failover occurs, the stale dev_set_promiscuity(-1) can be applied to the new slave and corrupt the promiscuity counter state, potentially pinning the device in IFF_PROMISC. For the CVSS the PR:L is used in the paranoid score because delegated CAP_NET_ADMIN, container root, or a network management service account may be sufficient in some deployments, although typical host level bonding control is closer to PR:H. The issue is not directly network reachable and is triggered through local network control plane operations rather than packet traffic. Impact is at least denial of service via kernel crash and may include limited confidentiality or integrity impact due to incorrect promiscuous mode state.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / Actionable Moderate in delegated CAP_NET_ADMIN deployments (with actual score 3)	YES	KASAN OOB NULLPTR NETWORK  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 4
* Final recommended bucket: **Borderline manual review recommended / Actionable Moderate in delegated CAP_NET_ADMIN deployments**::

## 2. Signal breakdown

Conservative signals:

* Reliable kernel crash / strong DoS: +1. The commit shows a NULL dereference in `bond_alb_monitor()` leading to kernel panic.
* Weak/indirect corruption candidate: +1. The stale `dev_set_promiscuity(-1)` can underflow the new slave promiscuity counter and pin `IFF_PROMISC`, but this is state corruption, not a strong memory corruption primitive.
* Availability impact realistic: +1. The demonstrated failure is host kernel panic.
* Requires CAP_NET_ADMIN in typical deployments: -2. Reliable triggering normally requires bonding device control, slave removal, or link management.
* Hard or unreliable race / special timing required: -1. The bug depends on a window between RCU observation and RTNL commit.

Paranoid additional interpretation:

* Local unprivileged trigger: +1. In deployments with unprivileged user namespaces and delegated network namespace administration, a non host root actor may obtain enough network control to exercise bonding paths.
* Confidentiality impact plausible: +1. Incorrectly pinned promiscuous mode may expose additional traffic to the host or namespace context.
* Integrity impact plausible: +1. The promiscuity counter state can be corrupted for the active slave.
* Privilege penalty reduced: the full -2 admin penalty is not applied in the paranoid score because container root, delegated CAP_NET_ADMIN, or service accounts may not be equivalent to full host root.

Not awarded:

* No remote/network-triggerable score. This is network control plane logic, not packet-triggered.
* No strong memory corruption score. The patch supports NULL dereference and counter state corruption, not UAF, OOB write, arbitrary write, type confusion, or attacker-controlled reclaim.
* No privilege escalation score. LPE is not supported by the patch context.

## 3. Reachability analysis

The realistic trigger is local control of a bonding interface in ALB mode, especially operations that remove or change the active slave while `bond_alb_monitor()` is running. In normal host deployments this requires CAP_NET_ADMIN or equivalent administrative network management rights. Namespace behavior matters because some systems allow unprivileged users to create user and network namespaces and gain CAP_NET_ADMIN inside that namespace, but bonding device creation and module availability may still be restricted by distribution policy. The affected path is not directly reachable from incoming packets and ALB bonding is configuration-dependent rather than universally enabled.

Call-site confidence: high. The relevant workqueue function, stale decision window, dereference, and fixed commit point are present in the supplied patch and commit message.

## 4. Severity interpretation

This behaves more like a borderline or actionable Moderate issue than an Important-class vulnerability. The demonstrated impact is a reliable kernel crash under a race plus persistent network interface state corruption. Theoretical confidentiality or integrity impact exists through incorrect promiscuous mode, but there is no evidence of a strong kernel memory corruption primitive or practical privilege escalation path. The main reason not to auto-close is the combination of race, kernel panic, and possible namespace-delegated CAP_NET_ADMIN exposure.

## 5. One-sentence report phrase

A race in `bond_alb_monitor()` can use stale `primary_is_promisc` state after RTNL acquisition, causing either a NULL dereference kernel panic or an incorrect promiscuity counter decrement that may leave a bonding slave pinned in promiscuous mode.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because the issue is a race in networking control plane code with demonstrated kernel panic and secondary interface state corruption, and the practical privilege requirement depends on namespace and CAP_NET_ADMIN delegation policy.

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

Patch: bonding: alb: re-check primary_is_promisc under RTNL in bond_alb_monitor [ Upstream
Commit: f7668762bf5fd6db9397de5c0514407489d9d815
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f7668762bf5fd6db9397de5c0514407489d9d815

Changed files:
  drivers/net/bonding/bond_alb.c
  kernel/workqueue.c
  kernel/kthread.c
  arch/x86/kernel/process.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=f7668762bf5fd6db9397de5c0514407489d9d815

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

The original Linux kernel CVE announcement for CVE-2026-74726 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74726

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:L/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: 2
  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).