[CVE-2025-37799][MODERATE 7.0] vmxnet3: Fix malformed packet sizing in vmxnet3_process_xdp

[CVE-2025-37799][MODERATE 7.0] vmxnet3: Fix malformed packet sizing in vmxnet3_process_xdp

[AL-KERNEL]

CVE: CVE-2025-37799
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: vmxnet3: Fix malformed packet sizing in vmxnet3_process_xdp
Commit: c4312c4d244aa58e811ff0297e013124d115e793
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c4312c4d244aa58e811ff0297e013124d115e793
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-37799
Analysis date: Mon, 12 Oct 2026 20:31:26 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2025-37799 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-37799

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.

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

CVE-2025-37799	MODERATE	https://www.kernelcve.org/list/?q=CVE-2025-37799 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 LEGACY=MODERATE_KPANIC RESULT=SAME (legacy and Aegis reconciliation agree; DECISION: both MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H';*CWE-200;CWE-908;CWE-130;Other CVSS 'AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:L';BEST CVSS score: '9.1';DESCR 'vmxnet3 XDP processing can use the receive buffer size instead of the actual packet length when preparing an XDP buffer. This makes data_end extend beyond the received packet and can transmit uninitialized contents from the same page as padding in a malformed oversized packet. Prior user or packet payload data was observed in the leaked bytes, so the issue provides a concrete network information disclosure primitive. It can also cause MTU related packet drops and connectivity failures. For the CVSS the PR:N value is used because a remote sender can supply traffic to the affected XDP path without obtaining a local account or privileges on the target. The issue is network reachable when a vmxnet3 interface runs an XDP program that transmits, redirects, or encapsulates the affected packets. Practical disclosure to an attacker depends on network topology and usually requires the attacker to control or observe the destination path that receives the malformed packet. Impact includes confidentiality loss and denial of service. No integrity impact is assigned because the code shows an incorrect readable length and data exposure but no out of bounds write or arbitrary write primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	MAYBE	OOB LEAK NETWORK KPANIC MEMORY PACKET  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	-	-	checked

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

ActionableScore=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: 4
* Conservative score: 5
* Raw paranoid score: 4
* Paranoid score: 5
* Applied conservative floor: 4 -> 5 because the patch establishes a concrete network-visible disclosure of uninitialized kernel-page contents, including prior user or packet payload data.
* Applied paranoid floor: 4 -> 5 for the same confirmed disclosure primitive. No additional speculative impact was added.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Positive signals:

* +2 Strong disclosure primitive. An incorrect `data_end` allows bytes beyond the actual received packet to be transmitted from the backing page. The commit confirms that prior user or packet payload was present in those bytes.
* +1 Confidentiality plausible. The leaked bytes are observable on the network and were confirmed in a packet capture.
* +1 Practical exploit chain. An ordinary HTTP request reached the affected XDP load-balancing path and produced a malformed packet containing unrelated page data.

Non-awarded signals:

* Direct remote reachability +2 was not awarded because the vulnerable path requires a previously configured vmxnet3 XDP load-balancing or forwarding setup. The subsequent packet trigger is remote, but establishment of the path is privileged control-plane activity.
* Reliable kernel crash or strong host DoS was not awarded. The demonstrated availability effect is packet loss and connectivity failure caused by oversized packets, not a kernel panic.
* Integrity was not awarded. The bug exposes memory through an incorrect readable packet extent but does not establish an OOB write or modification of protected state.
* Arbitrary kernel read was not awarded. Disclosure is constrained to residual contents in the affected page.
* B5-R does not apply because there is no retry-accumulated heap OOB write.
* B3-PENDING does not apply because no write to shared or file-backed storage occurs.
* No authorization decision is bypassed, so B4-PENDING does not apply.
* No UAF, controlled reclaim, privilege escalation, or function-pointer influence is established.

Arithmetic:

* Conservative: +2 disclosure primitive, +1 confidentiality, +1 practical chain = 4.
* Paranoid: +2 disclosure primitive, +1 confidentiality, +1 practical chain = 4.
* Important-preservation floor raises both results to 5. No unsupported remote, integrity, crash, or LPE points were added.

3. Reachability analysis

A remote sender can supply packets in the affected 128 byte to 3 KB ring0 size range after a vmxnet3 interface and XDP forwarding, redirect, or encapsulation program have been configured. The commit demonstrates this using an HTTP request through a Cilium XDP load balancer.

The attacker does not need UID 0, a local account, or a capability to send the triggering traffic. Therefore `HostAdminRequired=NO` for the runtime trigger. A separate administrator normally installs the XDP program and configures the vmxnet3 data path, so prior privileged setup exists, but that does not make each subsequent network trigger host-admin-only.

No namespace-scoped privilege is part of the attacker operation. BPF loading, XDP attachment, and netdevice management are privileged setup stages performed by the deployment administrator, while the evaluated attacker only supplies traffic.

The leak is delivered toward the backend or redirected destination. Practical attacker recovery of the bytes therefore depends on the attacker controlling or observing that destination path. The trigger itself is repeatable and does not involve a race or narrow timing window. The environment requires a vmxnet3 virtual NIC and an active XDP program using the affected path, but no unusual physical hardware is required.

4. Primitive and severity interpretation

The exact primitive is a bounded but substantial disclosure from the receive page. `rbi->len` describes the receive buffer rather than the actual packet. Supplying it to `xdp_prepare_buff()` extends `xdp->data_end` beyond the bytes identified by `rcd->len`. Later XDP forwarding or encapsulation consumes that enlarged range and emits residual page contents onto the network.

This is not a UAF, heap overwrite, shared-backing write, or authorization bypass. It is also not merely an internal OOB read because the unintended bytes reach externally visible network output. The observed disclosure of prior user or packet payload makes the primitive CLASS_A under the substantial kernel-disclosure category.

The practical evidence supports confidentiality loss and connection disruption. It does not establish arbitrary memory selection, integrity compromise, privilege escalation, or host-wide denial of service. The theoretical worst case is repeated leakage of sensitive packet or user payload data from reused receive pages, but not arbitrary kernel memory extraction.

`ImportantCandidate=YES` because a concrete kernel-data disclosure crosses the network boundary and should not be discarded as an ordinary malformed-packet bug. `AutoDowngradeAllowed=NO` because automatic downgrade would lose the confirmed disclosure primitive, even though the deployment and observation requirements may ultimately limit operational severity.

5. One-sentence report phrase

An incorrect vmxnet3 XDP packet length can transmit residual kernel-page contents containing prior user or packet data to a network destination, requiring mandatory review despite the absence of an OOB write or demonstrated privilege escalation.

6. Manual review recommendation

MANUAL CHECK REQUIRED

The disclosure is confirmed, but review is needed to determine which deployed XDP actions expose the padding, whether an untrusted endpoint can observe it, and what classes of data can occupy the affected receive pages.

7. Call-site confidence

Call-site confidence: high

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

Patch: vmxnet3: Fix malformed packet sizing in vmxnet3_process_xdp
Commit: c4312c4d244aa58e811ff0297e013124d115e793
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c4312c4d244aa58e811ff0297e013124d115e793

Commit description:

vmxnet3 driver's XDP handling is buggy for packet sizes using ring0 (that
is, packet sizes between 128 - 3k bytes).

We noticed MTU-related connectivity issues with Cilium's service load-
balancing in case of vmxnet3 as NIC underneath. A simple curl to a HTTP
backend service where the XDP LB was doing IPIP encap led to overly large
packet sizes but only for *some* of the packets (e.g. HTTP GET request)
while others (e.g. the prior TCP 3WHS) looked completely fine on the wire.

In fact, the pcap recording on the backend node actually revealed that the
node with the XDP LB was leaking uninitialized kernel data onto the wire
for the affected packets, for example, while the packets should have been
152 bytes their actual size was 1482 bytes, so the remainder after 152 bytes
was padded with whatever other data was in that page at the time (e.g. we
saw user/payload data from prior processed packets).

We only noticed this through an MTU issue, e.g. when the XDP LB node and
the backend node both had the same MTU (e.g. 1500) then the curl request
got dropped on the backend node's NIC given the packet was too large even
though the IPIP-encapped packet normally would never even come close to
the MTU limit. Lowering the MTU on the XDP LB (e.g. 1480) allowed to let
the curl request succeed (which also indicates that the kernel ignored the
padding, and thus the issue wasn't very user-visible).

Commit e127ce7 ("vmxnet3: Fix missing reserved tailroom") was too eager
to also switch xdp_prepare_buff() from rcd->len to rbi->len. It really needs
to stick to rcd->len which is the actual packet length from the descriptor.
The latter we also feed into vmxnet3_process_xdp_small(), by the way, and
it indicates the correct length needed to initialize the xdp->{data,data_end}
parts. For e127ce7 ("vmxnet3: Fix missing reserved tailroom") the
relevant part was adapting xdp_init_buff() to address the warning given the
xdp_data_hard_end() depends on xdp->frame_sz. With that fixed, traffic on
the wire looks good again.

Fixes: e127ce7 ("vmxnet3: Fix missing reserved tailroom")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Andrew Sauber <andrew.sauber@isovalent.com>
Cc: Anton Protopopov <aspsk@isovalent.com>
Cc: William Tu <witu@nvidia.com>
Cc: Martin Zaharinov <micron10@gmail.com>
Cc: Ronak Doshi <ronak.doshi@broadcom.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250423133600.176689-1-daniel@iogearbox.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/net/vmxnet3/vmxnet3_xdp.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=c4312c4d244aa58e811ff0297e013124d115e793

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

The original Linux kernel CVE announcement for CVE-2025-37799 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-37799

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:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:L
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
  The Best / paranoid CVSS score: 9.1

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: 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).