[CVE-2026-74398][MODERATE 7.0] ipv6: addrconf: bail out of dad_failure when state is no longer POSTDAD [ Upstream

[CVE-2026-74398][MODERATE 7.0] ipv6: addrconf: bail out of dad_failure when state is no longer POSTDAD [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74398
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ipv6: addrconf: bail out of dad_failure when state is no longer POSTDAD [ Upstream
Commit: 47b05836705b63dab93d9ac7c69a3a507375ef80
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=47b05836705b63dab93d9ac7c69a3a507375ef80
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74398
Analysis date: Sun, 16 Aug 2026 00:33:18 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
IPv6 addrconf DAD failure handling can race with concurrent IPv6 address deletion, allowing a stale DEAD address state to be overwritten and causing a second ipv6_del_addr call on a poisoned list entry, resulting in a kernel crash and requiring manual review due to network-adjacent trigger potential.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74398 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74398

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-2026-74398	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';CWE-362;CWE-667;*CWE-672;*CWE-416;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.4';DESCR 'IPv6 addrconf DAD failure handling can race with concurrent IPv6 address deletion. addrconf_dad_failure can move an address to POSTDAD and then temporarily release ifp lock, while another path can run ipv6_del_addr, mark the address DEAD, and remove the ifp list entry. The DAD failure path can then overwrite DEAD with ERRDAD and schedule dad_work, causing ipv6_del_addr to run again on an already poisoned list entry and crash the kernel. For the CVSS the PR:N is used for the paranoid score because a network adjacent attacker may trigger DAD failure with ICMPv6 Neighbor Discovery traffic without credentials if the target interface is reachable on the same L2 segment. The issue is not Internet routable in the normal case and exploitation usually requires access to the same local link plus a timing race with address removal. Impact is at least denial of service via kernel crash. In the worst defensible case it may have limited confidentiality or integrity impact because the bug involves a race and stale list state in kernel memory, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	REMOTE OOB LOCK DANGER NETWORK HARDWARE IPV6 KPANIC 	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

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

## 2. Signal breakdown

Conservative signals:

* Weak/indirect corruption candidate: +1
  The bug can cause a second `ipv6_del_addr()` on an already removed and poisoned list entry. This is stale list/lifetime state, but the patch shows a crash on poison pointer rather than controlled reuse or arbitrary write.

* Real lifetime corruption: +1
  `ipv6_del_addr()` can mark the address DEAD and remove it from `if_list`, while `addrconf_dad_failure()` later overwrites the state and schedules new work against the same object lifecycle.

* Reliable kernel crash / strong DoS: +1
  The commit includes a concrete general protection fault in `ipv6_del_addr()` from `addrconf_dad_work`.

* Broad/default/common subsystem: +1
  IPv6 addrconf and DAD are common kernel networking functionality and are enabled in many default deployments.

* Hard or unreliable race / special timing required: -1
  Exploitation requires a timing window between DAD failure handling and concurrent IPv6 address deletion.

* Common networking core path: +1
  This is in IPv6 address configuration and DAD handling, not a rare driver-only path.

Paranoid delta:

* Remote reachable / network-triggerable: +2
  A same-link attacker may be able to influence DAD failure using IPv6 Neighbor Discovery traffic. This is best treated as network-adjacent rather than Internet-routable.

* Race-UAF downgrade rule applied.
  No attacker-controlled reclaim, stale object replacement, write-after-free, callback control, refcount takeover, or arbitrary write is shown. Therefore this remains weak corruption plus lifetime corruption, not strong LPE-class memory corruption.

Paranoid score is therefore capped at 5 for practical triage.

## 3. Reachability analysis

A local attacker with control over IPv6 address lifecycle can more reliably create the address deletion side of the race, but that often requires `CAP_NET_ADMIN` or equivalent network administration control. A network-adjacent attacker on the same L2 segment may be able to trigger the DAD failure side through IPv6 Neighbor Discovery behavior, but reliable exploitation still depends on a concurrent address deletion or lifecycle transition. This is not normally reachable from the public Internet because DAD and Neighbor Discovery are link-local mechanisms.

Namespaces and containers matter. If a container or delegated network namespace gives an untrusted user control over IPv6 address configuration, practical reachability can be closer to local low privilege. In ordinary host deployments, reliable local triggering is more likely to require network administration capability.

## 4. Severity interpretation

This is more than an ordinary low-risk correctness bug because the patch fixes a real race leading to stale list state and a demonstrated kernel crash. It is best treated as Actionable Moderate at minimum.

The realistic impact shown by the patch is DoS via kernel crash. Theoretical memory corruption concern exists because the bug involves stale state after list deletion, but there is no demonstrated reclaim primitive, arbitrary write, object replacement, callback dispatch, or privilege escalation path. Therefore it should not be promoted to Strong Important solely on memory corruption grounds.

## 5. One-sentence report phrase

IPv6 addrconf DAD failure handling can race with concurrent IPv6 address deletion, allowing a stale DEAD address state to be overwritten and causing a second ipv6_del_addr call on a poisoned list entry, resulting in a kernel crash and requiring manual review due to network-adjacent trigger potential.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the issue combines a race, stale lifetime/list state, a demonstrated kernel crash, and possible same-link network influence over DAD failure. No strong LPE primitive is shown, but the networking exposure and lifetime corruption make it unsuitable for automatic closure.

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

Patch: ipv6: addrconf: bail out of dad_failure when state is no longer POSTDAD [ Upstream
Commit: 47b05836705b63dab93d9ac7c69a3a507375ef80
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=47b05836705b63dab93d9ac7c69a3a507375ef80

Changed files:
  net/ipv6/addrconf.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=47b05836705b63dab93d9ac7c69a3a507375ef80

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

The original Linux kernel CVE announcement for CVE-2026-74398 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74398

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:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 6.4

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: 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).