[CVE-2026-97939][MODERATE REGULAR] ipmr: account multicast table and route memory [ Upstream

[CVE-2026-97939][MODERATE REGULAR] ipmr: account multicast table and route memory [ Upstream

[AL-KERNEL]

CVE: CVE-2026-97939
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ipmr: account multicast table and route memory [ Upstream
Commit: 0264b3ee09b118fec8a5471b4ca288f8ab84722f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0264b3ee09b118fec8a5471b4ca288f8ab84722f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97939
Analysis date: Sat, 26 Sep 2026 15:36:55 -0400
ActionableScore: 3
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-97939 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97939

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: NO

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

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

CVE-2026-97939	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-97939 CHECK WITH IMPACT FROM ORIG NN MODERATE	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-400;CWE-770;*CWE-401;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'IPv4 and IPv6 multicast routing tables created through MRT_TABLE and MRT6_TABLE were not charged to the memory cgroup. A local user able to create a user and network namespace can obtain CAP_NET_ADMIN in the child network namespace and repeatedly create new multicast routing table identifiers, causing unreclaimable kernel slab memory to accumulate until network namespace teardown. For the CVSS the PR:L is used because reliable triggering requires local code execution and namespace setup, even though full host administrative privileges are not required. The issue is not directly network reachable. Impact is resource exhaustion and potential host denial of service. It does not provide evidence of memory corruption, information disclosure, integrity impact, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 3)	YES	REMOTE DANGER SIMPLEFIX NETWORK IPV6  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	NO	NO	checked

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

ActionableScore=3
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=YES
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 3
* Raw paranoid score: 3
* Paranoid score: 3
* Final recommended bucket: **Ordinary Moderate**::

The conservative and paranoid scores are identical. The patch establishes a namespace accounting bypass and potential host resource exhaustion, but does not establish memory corruption, a lifetime violation, confidentiality impact, integrity impact, or privilege escalation.

2. Signal breakdown

* +1 Local unprivileged trigger. The supplied commit explicitly states that a netadmin in an attacker-created user and network namespace can create multicast routing tables. A local user can normally obtain CAP_NET_ADMIN in the child network namespace after creating the user namespace.
* +1 Cross-boundary isolation or policy bypass. The mr_table allocations were not charged to the memory cgroup, allowing memory allocated by a constrained namespace workload to accumulate as unaccounted host unreclaimable slab memory.
* +1 Availability impact realistic. Repeated creation of unseen MRT_TABLE or MRT6_TABLE identifiers accumulates mr_table objects until network namespace teardown and can consume host memory.

Important non-awarded signals:

* +0 Memory corruption. No UAF, double free, OOB access, invalid pointer use, refcount corruption, or overwrite is established.
* +0 Concrete persistent resource leak. The objects are retained intentionally until network namespace teardown. This is an accounting omission and resource-exhaustion condition, not an unrecoverable missing put or permanently leaked reference.
* +0 Reliable kernel crash. The supplied evidence supports possible memory exhaustion, not a direct panic or deterministic kernel crash.
* +0 Confidentiality and integrity. No disclosure, unauthorized modification, protected-object access, or privilege escalation primitive is established.
* +0 Remote reachability. The vulnerable operation is a local multicast-routing control-plane operation and is not directly reachable through ordinary network packet traffic.
* +0 Strong exploitation leverage. Repeated table creation controls allocation count but does not provide attacker-controlled corruption, target selection, object replacement, or post-free reuse.

3. Reachability analysis

The evaluated attacker is a local user who can create a user namespace and a network namespace, then obtain CAP_NET_ADMIN within the child network namespace. The supplied commit explicitly identifies this attacker model and states that such a netadmin can create many IPv4 and IPv6 multicast routing tables through MRT_TABLE and MRT6_TABLE.

The relevant multicast routing table creation operation is namespace-scoped because the tables are linked into the per-network-namespace list and are released during network namespace teardown. The complete described trigger is therefore reachable below host-admin privilege when unprivileged user namespace creation is enabled by the deployment policy.

No prior host-created device, special hardware, boot option, firmware interaction, privileged BPF setup, or network exposure is required by the supplied evidence. The attacker can repeatedly request unseen table identifiers, so this is not a narrow timing race.

4. Primitive and severity interpretation

The exact primitive is unaccounted kernel memory allocation. Each new multicast routing table identifier can allocate an mr_table object that remains associated with the attacker-controlled network namespace until that namespace is destroyed. Before the fix, these allocations used non-accounted allocation flags, allowing their slab consumption to bypass memory-cgroup accounting.

This is neither active structured-object lifetime corruption nor fixed stale storage. There is no stale pointer, no object reuse, no cleanup UAF, no repeated release operation, and no refcount mutation through freed storage. The issue is therefore PrimitiveClass=NONE.

The demonstrated consequence is host memory pressure or host denial of service through unaccounted unreclaimable slab growth. The practical impact depends on namespace policy, available host memory, memory pressure behavior, and the attacker's ability to sustain creation of new table identifiers. The patch also notes that unresolved MFC entries are not the primary unbounded mechanism because they expire after approximately ten seconds and are bounded by the socket receive queue.

ImportantCandidate=NO because the patch establishes a resource-accounting bypass but no meaningful memory-corruption, authorization-bypass, ownership, confidentiality, integrity, or privilege-escalation primitive. AutoDowngradeAllowed=YES because this is a bounded resource-exhaustion issue without unresolved kernel-corruption leverage.

Likely operational severity is ordinary Moderate. Systems that disable unprivileged user namespaces or restrict namespace creation substantially reduce exposure. Systems that allow untrusted users or containers to create user and network namespaces should apply the fix according to their normal kernel-update schedule.

5. One-sentence report phrase

A local user able to create a user and network namespace can create many unaccounted IPv4 or IPv6 multicast routing tables, potentially exhausting host slab memory and causing denial of service.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch establishes a memory-cgroup accounting omission and potential resource exhaustion, but does not establish memory corruption, a security-boundary escape beyond resource isolation, confidentiality or integrity impact, or privilege escalation.

7. Call-site confidence

Call-site confidence: medium

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

Patch: ipmr: account multicast table and route memory [ Upstream
Commit: 0264b3ee09b118fec8a5471b4ca288f8ab84722f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0264b3ee09b118fec8a5471b4ca288f8ab84722f

Changed files:
  net/ipv4/ipmr.c
  net/ipv4/ipmr_base.c
  net/ipv6/ip6mr.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=0264b3ee09b118fec8a5471b4ca288f8ab84722f

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

The original Linux kernel CVE announcement for CVE-2026-97939 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97939

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:L/PR:L/UI:N/S:U/C:N/I:N/A:L
  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: unknown
  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: 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).