[CVE-2026-53214][LOW] ipv6: Fix a potential NPD in cleanup_prefix_route() [ Upstream

[CVE-2026-53214][LOW] ipv6: Fix a potential NPD in cleanup_prefix_route() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-53214
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: ipv6: Fix a potential NPD in cleanup_prefix_route() [ Upstream
Commit: 5f82b02b4059ddc06e4fcfd057bfb59fd6885cd2
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5f82b02b4059ddc06e4fcfd057bfb59fd6885cd2
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53214
Analysis date: Mon, 29 Jun 2026 10:24:12 -0400
ActionableScore: 3
ActionableScore lower bound: 1
Actionable bucket: Borderline Ordinary Moderate / namespace exposure check
Manual review required: NO

Summary:
A local actor with IPv6 rtnetlink configuration privileges, or potentially an unprivileged user through delegated network namespaces, can trigger a NULL pointer dereference in `cleanup_prefix_route()` by causing `addrconf_get_prefix_route()` to return `fib6_null_entry`, resulting in a kernel crash.

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

The original Linux kernel CVE announcement for CVE-2026-53214 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53214

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: LOW
Manual review required: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-53214	LOW	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';**CWE-476;*CWE-20;CWE-703;BEST CVSS score: '5.5';DESCR 'cleanup_prefix_route can dereference fib6_null_entry after addrconf_get_prefix_route returns the IPv6 null route sentinel whose fib6_table pointer is NULL. A local actor can trigger the vulnerable path through rtnetlink IPv6 address deletion when the route lookup returns this sentinel, causing a kernel NULL pointer dereference and system crash. For the CVSS the PR:L is used because reliable triggering requires local code execution and netlink based network configuration privileges, commonly CAP_NET_ADMIN in a network namespace. The issue is not directly network reachable and is not triggered by ordinary packet traffic. Impact is denial of service only because the patch evidence shows a NULL pointer dereference and does not indicate UAF, OOB access, arbitrary write, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Borderline Ordinary Moderate / namespace exposure check (with actual score 2)  SKIP CVE-2026-53214  SKIP The Fixes patch not applied yet, so unlikely that actual: 5eb902b8e7193cdcb33242af0a56502e6b5206e9 YES  NO NO unknown 	MAYBE	REMOTE KASAN OOB LOCK NULLPTR NETWORK HARDWARE IPV6  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=3
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 3
* Final recommended bucket: **Borderline Ordinary Moderate / namespace exposure check**::

## 2. Signal breakdown

Conservative scoring:

* Reliable kernel crash / strong DoS: +1
  The trace shows a NULL pointer dereference through `fib6_null_entry->fib6_table == NULL` followed by `spin_lock_bh(&table->tb6_lock)`.

* Broad/default/common subsystem: +1
  IPv6 addrconf and rtnetlink are core networking configuration paths, although this is not a packet receive path.

* Requires CAP_NET_ADMIN in typical deployments: -2
  The demonstrated path is `inet6_rtm_deladdr()` via rtnetlink IPv6 address deletion, normally requiring CAP_NET_ADMIN.

Conservative total: 1

Paranoid adjustment:

* Local unprivileged trigger: +1
  On systems with unprivileged user namespaces and network namespaces enabled, an unprivileged local user may obtain CAP_NET_ADMIN inside a new netns and exercise this path.

Paranoid total: 3

Not counted:

* No generic memory corruption. This is a NULL pointer dereference on a sentinel route object, not UAF, OOB write, double free, arbitrary write, or object reclaim.
* No privilege escalation signal. The patch does not show a corruption primitive suitable for LPE.
* No remote reachable signal. Ordinary IPv6 packets do not directly trigger this path.

## 3. Reachability analysis

The realistic trigger is local rtnetlink control-plane activity that deletes an IPv6 address and reaches `cleanup_prefix_route()`. In the initial network namespace this usually requires CAP_NET_ADMIN, so conservative scoring treats it as privileged. In environments allowing unprivileged user namespaces plus network namespaces, a local unprivileged user may create a namespace, gain CAP_NET_ADMIN inside it, and potentially trigger the bug against the host kernel, which justifies the paranoid score. The path is not directly network-triggerable and is not part of ordinary packet processing.

## 4. Severity interpretation

This behaves like an ordinary Moderate local DoS in the conservative case. The worst credible interpretation is borderline actionable only because namespace delegation may reduce the effective privilege requirement. There is no evidence of a practical memory corruption primitive or privilege escalation path. The theoretical impact remains kernel crash availability loss, not confidentiality or integrity compromise.

## 5. One-sentence report phrase

A local actor with IPv6 rtnetlink configuration privileges, or potentially an unprivileged user through delegated network namespaces, can trigger a NULL pointer dereference in `cleanup_prefix_route()` by causing `addrconf_get_prefix_route()` to return `fib6_null_entry`, resulting in a kernel crash.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: not because of memory corruption, but to verify product-specific namespace policy. If unprivileged user namespaces or delegated CAP_NET_ADMIN are disabled, this can likely be treated as ordinary Moderate and auto-closed for urgent-response purposes.

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

Patch: ipv6: Fix a potential NPD in cleanup_prefix_route() [ Upstream
Commit: 5f82b02b4059ddc06e4fcfd057bfb59fd6885cd2
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5f82b02b4059ddc06e4fcfd057bfb59fd6885cd2

Changed files:
  mm/kasan/common.c
  kernel/locking/lockdep.c
  kernel/locking/spinlock.c
  net/ipv6/addrconf.c
  net/core/rtnetlink.c
  net/netlink/af_netlink.c
  net/socket.c
  arch/x86/entry/syscall_64.c
  arch/x86/entry/entry_64.S

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=5f82b02b4059ddc06e4fcfd057bfb59fd6885cd2

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

The original Linux kernel CVE announcement for CVE-2026-53214 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53214

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 3

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).