[CVE-2026-97597][LOW] ipv6: flowlabel: cap duplicate leases per socket

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

CVE: CVE-2026-97597
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: ipv6: flowlabel: cap duplicate leases per socket
Commit: 2f1a6dd5c80ceb902f50449efe899f29cd7918e3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2f1a6dd5c80ceb902f50449efe899f29cd7918e3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97597
Analysis date: Fri, 25 Sep 2026 14:14:29 -0400
ActionableScore: 2
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-2026-97597 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97597

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-2026-97597	LOW	https://www.kernelcve.org/list/?q=CVE-2026-97597 CHECK WITH IMPACT FROM ORIG NN LOW	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 'An unprivileged local process can repeatedly request the same shareable IPv6 flow label and cause ipv6_flowlabel_get to allocate another ipv6_fl_socklist lease for every successful GET operation. The compatible shared label path did not apply a per socket lease admission limit, allowing the lease list and kernel memory consumption to grow without bound. For the CVSS the PR:L value is used because a local user process and access to the IPv6 socket interface are required, while administrative capabilities are not required for requests below the limit. The issue is not directly network reachable because receiving remote IPv6 traffic does not execute the vulnerable allocation sequence on behalf of an attacker. Impact is primarily local denial of service through sustained kernel memory consumption, memory pressure, and possible host OOM. No UAF, OOB access, information disclosure, or arbitrary write primitive is supported by the affected code, so confidentiality and integrity remain unaffected.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)  SKIP CVE-2026-97597 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	REMOTE LOCK NETWORK IPV6  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Local unprivileged trigger. The commit explicitly states that an unprivileged process can repeatedly obtain leases for one shareable IPv6 flow label.
* +1 Strong resource-exhaustion DoS potential. Repeated requests retain an unbounded number of kernel lease objects on one open socket and can consume host memory until significant memory pressure or OOM occurs.
* No concrete persistent resource leak point was awarded. The objects remain linked to the socket rather than becoming unreachable, and normal socket destruction is expected to recover them.
* No additional availability point was awarded because memory exhaustion and the resulting possible OOM are the same consequence.
* No corruption point was awarded. The patch establishes unbounded allocation but no UAF, OOB access, stale pointer, overwrite, or refcount corruption.
* No confidentiality or integrity point was awarded.
* No remote-reachability point was awarded. Remote IPv6 packets do not independently perform the required flow-label GET operations.
* No common networking data-path point was awarded. This is a socket control operation rather than ordinary packet processing.
* No privilege penalty was applied because below-host-admin reachability is explicitly established.
* No namespace-boundary bonus was awarded. Host memory consumption is relevant, but no separate cgroup or memory-accounting bypass is demonstrated.

3. Reachability analysis

An ordinary local process can open an IPv6 socket and repeatedly issue successful GET requests for a compatible shareable flow label. Host administrator privileges are not required for requests below the newly introduced limit, so HostAdminRequired is NO.

The vulnerable operation itself is unprivileged and does not depend on a namespaced capability. The patch deliberately uses capable(CAP_NET_ADMIN), rather than ns_capable(), for exemption from the new limit. Consequently, CAP_NET_ADMIN acquired in an attacker-created user namespace or network namespace cannot provide an unlimited exemption. NamespaceScopedPrivilege is therefore NO for the security-relevant exemption.

No prior privileged setup, special hardware, unusual boot mode, or timing race is identified. IPv6 support and access to the local socket API are required. The attack requires sustained local requests and keeping the affected socket alive. It is not directly triggerable through network traffic alone.

4. Primitive and severity interpretation

The exact primitive is attacker-driven, unbounded retention of ipv6_fl_socklist lease allocations associated with an open socket. This is resource exhaustion, not memory corruption and not a lifetime violation.

There is no real UAF, post-lifetime access, double release, refcount mutation, controlled reclaim, or arbitrary write. The retained objects remain valid and reachable through the socket lease list until cleanup. PrimitiveClass is therefore CLASS_C because the demonstrated security consequence is local availability loss through memory pressure or possible OOM.

The practical consequence is a local DoS requiring sustained allocation activity. Stronger consequences such as information disclosure, kernel-state modification, privilege escalation, or code execution are unsupported. ImportantCandidate is NO because no Important-preserving primitive or security-boundary bypass is established.

AutoDowngradeAllowed is YES because this is a bounded-class resource-exhaustion issue without unresolved corruption leverage. It can be handled as an ordinary Moderate or Low-like issue according to product exposure and operational policy.

5. One-sentence report phrase

An unprivileged local process can repeatedly acquire duplicate IPv6 flow-label leases on one socket and consume unbounded kernel memory, potentially causing memory pressure or host OOM without establishing a memory-corruption or privilege-escalation primitive.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch establishes a straightforward local resource-exhaustion condition with no UAF, corruption, disclosure, authorization bypass, or unresolved Important-grade primitive.

7. Call-site confidence

Call-site confidence: high

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

Patch: ipv6: flowlabel: cap duplicate leases per socket
Commit: 2f1a6dd5c80ceb902f50449efe899f29cd7918e3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2f1a6dd5c80ceb902f50449efe899f29cd7918e3

Commit description:

ipv6_flowlabel_get() allocates an ipv6_fl_socklist entry for every
successful GET. The recheck path for a compatible existing flowlabel
links another lease without applying any lease admission check. Repeated
GET requests for one shareable label can therefore grow a socket's lease
list without bound.

Reject a new unprivileged lease once the socket already holds
FL_MAX_PER_SOCK leases. Check this on the shared recheck path so reuse
of a globally interned label, including the fl_intern() collision path,
is covered as well. New-label admission remains under the existing
mem_check() policy.

Use capable(CAP_NET_ADMIN) rather than ns_capable(), matching
mem_check(). An unprivileged user must not bypass the cap by creating a
user namespace and a netns where they have CAP_NET_ADMIN, which would
still consume host memory.

Check the capability only when the socket reaches the limit, so
successful unprivileged GET requests below the cap do not generate a
capability audit. Do the admission check before updating linger and
expires so a rejected GET does not refresh the shared label, matching
the existing socket-list allocation failure path.

Fixes: 1da177e ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Reported-by: Vega <vega@nebusec.ai>
Suggested-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Zhiling Zou <zhilinz@nebusec.ai>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/83f8535972ff6e3741548476a1d50dec24c758be.1788415194.git.zhilinz@nebusec.ai
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/ipv6/ip6_flowlabel.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=2f1a6dd5c80ceb902f50449efe899f29cd7918e3

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

The original Linux kernel CVE announcement for CVE-2026-97597 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97597

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: 2

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).