[CVE-2025-37998][LOW] openvswitch: Fix unsafe attribute parsing in output_userspace()

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

CVE: CVE-2025-37998
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: openvswitch: Fix unsafe attribute parsing in output_userspace()
Commit: 47f7f00cf2fa3137d5c0416ef1a71bdf77901395
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=47f7f00cf2fa3137d5c0416ef1a71bdf77901395
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-37998
Analysis date: Mon, 12 Oct 2026 22:15:17 -0400
ActionableScore: 3
ActionableScore lower bound: 1
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2025-37998 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-37998

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: YES

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

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

CVE-2025-37998	LOW	https://www.kernelcve.org/list/?q=CVE-2025-37998 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=LOW RESULT=DIFF TEMP_DISTANCE_MERGE_SKIP=AEGIS_NO_POSITIVE_SEVERITY_EVIDENCE (independent Legacy and Aegis differ; FINAL: LOW, Aegis: MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';*CWE-20;CWE-125;CWE-1284;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:H';BEST CVSS score: '6.6';DESCR 'Open vSwitch output_userspace manually iterates over nested Netlink attributes without first confirming that each attribute header and payload fit inside the remaining buffer. A malformed userspace action can therefore make the kernel inspect data beyond the valid nested attribute and may result in a kernel crash, incorrect upcall metadata, or limited kernel information exposure. For the CVSS the PR:L value is used for the paranoid score because a container root, network management service, or local account with delegated CAP_NET_ADMIN may be able to submit Open vSwitch control plane actions without having unrestricted host root access. The issue is not directly reachable through ordinary network packets because the malformed data must enter through the Open vSwitch Netlink control plane. Impact is at least a local denial of service and may include limited confidentiality or integrity impact due to unsafe out of bounds parsing. Manual review should confirm whether existing Netlink policy validation blocks malformed nested attributes before output_userspace is reached.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 2)	MAYBE	SIMPLEFIX LINUS KPANIC_UNSUPPORTED_REMOVED	-	-	checked

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

ActionableScore=3
ActionableScoreLower=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 3
* Paranoid score: 3
* No floor or cap was applied.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

Conservative signals:

* +1 Weak or indirect corruption candidate. The manual loop tests only `rem > 0` and does not apply `nla_ok()`, so it can inspect an incomplete or malformed nested attribute outside its valid logical bounds.
* No reliable-crash point. The commit does not report a crash, panic, disclosure, or reproducer, and complete malformed-input reachability is not shown.
* No privilege penalty. Open vSwitch control operations commonly involve `CAP_NET_ADMIN`, but the supplied code does not establish whether the complete vulnerable sequence requires host-admin-equivalent privilege.

Additional paranoid signals:

* +1 Reliable DoS concern. A malformed attribute with a non-progressing aligned length can prevent `nla_next()` from reducing `rem`, creating a technically plausible infinite kernel loop.
* +1 Confidentiality concern. A malformed attribute classified as `OVS_USERSPACE_ATTR_USERDATA` is stored in `upcall.userdata`. Normal upcall semantics may subsequently copy its declared payload to userspace, creating a plausible OOB disclosure path, but the relevant upcall construction code is not supplied.

Not awarded:

* No UAF, heap overwrite, arbitrary write, controlled reclaim, refcount corruption, or lifetime violation is established.
* No integrity point is awarded merely because malformed metadata could affect upcall fields.
* No remote-reachability point is awarded. Ordinary packets do not directly carry these Open vSwitch action attributes.
* No local-unprivileged point is awarded because the complete capability and namespace path is unresolved.
* No extra availability point is awarded for the same possible infinite-loop consequence.
* B5-R does not apply because there is no confirmed retry-accumulated OOB write.
* B3-PENDING does not apply because there is no shared-backing write.
* B4-PENDING does not apply because no authorization decision changes from DENY to ALLOW.

3. Reachability analysis

The vulnerable function consumes nested attributes from an Open vSwitch userspace action. Creating or modifying Open vSwitch datapath actions normally involves a Generic Netlink control-plane operation and some form of `CAP_NET_ADMIN`, followed by execution of the configured action on a packet.

The supplied patch does not show the ingress policy, action-validation call path, capability check, or whether malformed nested attributes can survive earlier validation. It also does not establish whether all required operations can be completed with `CAP_NET_ADMIN` in an attacker-created user and network namespace. Therefore both host-admin requirement and namespace-scoped privilege remain unknown.

No prior host setup, special hardware, boot option, or race is established. The defect is deterministic parsing behavior rather than a timing issue if malformed input reaches `output_userspace()`.

4. Primitive and severity interpretation

The exact primitive is unsafe nested Netlink attribute parsing. The old loop processes an attribute whenever any bytes remain, whereas `nla_for_each_nested()` requires the next attribute header and declared payload to fit within the remaining buffer.

The directly supported behavior is an invalid structured read or non-progressing parse. This is Class C because no kernel write, UAF, ownership violation, or independently useful corruption primitive is established. A malformed `USERDATA` attribute provides a plausible disclosure route because its pointer is retained for an upcall, but the downstream copy and complete attacker reachability are not visible.

The practical patch-supported consequence is malformed-state consumption, with possible CPU lockup or invalid read. Kernel information disclosure is a defensible paranoid possibility rather than a confirmed result. Privilege escalation and arbitrary kernel read or write are unsupported.

ImportantCandidate is NO because the evidence does not establish a Class A primitive or a strong unresolved Class B corruption mechanism. AutoDowngradeAllowed is YES because the issue remains a constrained parser defect without demonstrated memory modification, lifetime corruption, authorization bypass, or cross-boundary primitive.

5. One-sentence report phrase

Unsafe iteration over malformed nested Open vSwitch Netlink attributes can cause invalid attribute consumption, a possible non-progressing kernel loop, and potentially an out-of-bounds userspace upcall copy if malformed actions reach output_userspace.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm whether earlier Open vSwitch action validation accepts malformed nested attributes, which capability namespace governs submission, and whether malformed `upcall.userdata` can copy bytes beyond the validated action buffer.

7. Call-site confidence

Call-site confidence: medium

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

Patch: openvswitch: Fix unsafe attribute parsing in output_userspace()
Commit: 47f7f00cf2fa3137d5c0416ef1a71bdf77901395
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=47f7f00cf2fa3137d5c0416ef1a71bdf77901395

Commit description:

This patch replaces the manual Netlink attribute iteration in
output_userspace() with nla_for_each_nested(), which ensures that only
well-formed attributes are processed.

Fixes: ccb1352 ("net: Add Open vSwitch kernel components.")
Signed-off-by: Eelco Chaudron <echaudro@redhat.com>
Acked-by: Ilya Maximets <i.maximets@ovn.org>
Acked-by: Aaron Conole <aconole@redhat.com>
Link: https://patch.msgid.link/0bd65949df61591d9171c0dc13e42cea8941da10.1746541734.git.echaudro@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/openvswitch/actions.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=47f7f00cf2fa3137d5c0416ef1a71bdf77901395

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

The original Linux kernel CVE announcement for CVE-2025-37998 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-37998

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:H/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 6.6

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).