* [CVE-2026-98556][MODERATE REGULAR] gve: DQO: reject TSO packets with an out of range MSS [ Upstream
@ 2026-10-19 6:31 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-19 6:31 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98556
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: gve: DQO: reject TSO packets with an out of range MSS [ Upstream
Commit: 2dc3ae3942e151fef254b7bbb65c832192ad2069
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2dc3ae3942e151fef254b7bbb65c832192ad2069
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98556
Analysis date: Mon, 19 Oct 2026 02:31:02 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
An attacker controlled oversized GSO MSS can be truncated to zero in an active GVE DQO TSO descriptor submitted by the privileged host transmit path, creating a credible guest to host device integrity and availability review candidate without establishing kernel memory corruption or VM escape.
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ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98556 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98556
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: YES
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-98556 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98556 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=0 LEGACY=MODERATE RESULT=DIFF (final Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-20;CWE-197;CWE-1284;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.7';DESCR 'An oversized attacker influenced TSO MSS can reach the gve DQO transmit path because forwarded GSO packets are not bounded by the normal MTU checks and gso_features_check does not validate gso_size. A value such as 16384 is truncated to zero when stored in the 14 bit MSS field of the hardware TSO context descriptor, which can result in malformed transmit processing and possible queue or device disruption. A local packet socket user or a guest connected through a tap can provide the relevant GSO metadata. For the CVSS the PR:L value reflects that a local user context or control of a guest networking context is required for reliable triggering. The issue is not a conventional remote network attack because ordinary packets do not directly carry virtio_net_hdr metadata, but a guest to host adjacent path is plausible in virtualized deployments. Impact is primarily denial of service or loss of network availability. No UAF, OOB access, or arbitrary memory write is established by the affected path. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 5.7 and the production ActionableScore returned 4 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were KP and FD specialist checks stage MODERATE_KPANIC to MODERATE because KP specialist did not establish a qualifying panic. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP and V41_INHERITED_KPANIC_PROMOTION_BLOCKED and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 3.5 and ActionableScore 0 with primitive class CLASS_C and manual review RECOMMENDED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 4) MAYBE REMOTE OOB NETWORK SKB HARDWARE LINUS PACKET DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP V41_INHERITED_KPANIC_PROMOTION_BLOCKED MANUAL_REVIEW_REQUIRED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=4
ActionableScoreLower=3
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
## 1. ActionableScore
* Raw conservative score: 3
* Conservative score: 3
* Raw paranoid score: 4
* Paranoid score: 4
* No floor or cap was applied.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
## 2. Signal breakdown
Conservative signals:
* +2 Strong attacker-influenced semantic reinterpretation. An arbitrary `gso_size` accepted in the SKB and `virtio_net_hdr` representation is written into a 14-bit active TSO descriptor field. A value of 16384 is therefore reinterpreted by the device as MSS zero.
* +1 Firmware or device-mediated external influence. Guest or packet-socket input reaches a host-created GVE descriptor that is consumed by the privileged NIC data path.
* Total: 3.
Paranoid addition:
* +1 Unresolved availability consequence. The device receives an unsupported active TSO descriptor with MSS zero. Queue or interface disruption is technically plausible, although the supplied evidence does not establish a reliable device hang or host panic.
* Total: 4.
Important non-awarded signals:
* No UAF, heap OOB write, arbitrary write, controlled reclaim, or kernel-memory overwrite is established.
* The descriptor write is in bounds. The defect is truncation and semantic corruption of the descriptor value.
* Direct remote reachability was not awarded because ordinary network packets cannot directly specify `virtio_net_hdr.gso_size`.
* Local-unprivileged bonus was not awarded because packet sockets generally require `CAP_NET_RAW`, and exact guest-side privilege requirements are not supplied.
* Reliable kernel crash was not awarded.
* Confidentiality, protected-state integrity, LPE, and VM escape were not awarded.
* NEW52 B5-R does not apply because there is no retry-accumulated heap OOB write.
* NEW53 B3-PENDING does not apply because no shared file-backed storage write is involved.
* NEW54 B4-PENDING does not apply because no authorization decision changes from DENY to ALLOW.
V33 applies as a review-candidate rule:
1. Attacker influence: arbitrary `gso_size` can originate from a guest behind a tap or a packet-socket producer.
2. Active state write: the truncated value is written into the active TSO context descriptor.
3. Privileged consumer: the host GVE transmit path submits the descriptor to the NIC.
4. Trust boundary: a guest-to-host virtual-network boundary is explicitly credible.
5. Consequence: malformed device processing is established, while host-wide availability and non-DoS consequences remain unresolved.
## 3. Reachability analysis
A guest behind a tap or a local packet-socket producer can provide the oversized GSO metadata. The commit explicitly states that these sources can supply an arbitrary `gso_size`, and that normal MTU and GSO checks do not reject it.
The guest path is below host-administrator privilege, so `HostAdminRequired=NO`. It requires prior host configuration connecting the guest or tap forwarding path to a GVE DQO interface, but the attacker does not need host administration after that path is exposed.
For a local packet-socket actor, `CAP_NET_RAW` is normally relevant. Whether that capability and the complete forwarding path can be established entirely inside an attacker-created user or network namespace is not shown, so `NamespaceScopedPrivilege=UNKNOWN`.
The vulnerable system requires GVE hardware or its corresponding virtual device and the DQO transmit path. No timing race or retry sequence is required.
## 4. Primitive and severity interpretation
The exact primitive is attacker-influenced truncation of active structured device state. An oversized SKB MSS is converted from its software representation into a narrower 14-bit descriptor field, changing 16384 into zero. The malformed descriptor is then consumed by the host NIC path.
This is not stale storage, a UAF, an OOB write, or a cleanup-only lifetime failure. It is a CLASS_B active-state and trust-boundary candidate because the corrupted descriptor is operational rather than diagnostic, a privileged downstream consumer exists, and the guest-to-host boundary is credible.
The demonstrated consequence is submission of an invalid TSO descriptor. Packet loss or malformed transmit behavior is strongly implied. Queue or interface disruption is unresolved but defensible for paranoid review. Host panic, host memory corruption, information disclosure, privilege escalation, and VM escape are not demonstrated.
`ImportantCandidate=YES`, `ManualReview=REQUIRED`, and `AutoDowngradeAllowed=NO` follow from V33. They preserve review of the active descriptor and guest-to-host chain but do not claim proven Important severity.
## 5. One-sentence report phrase
An attacker controlled oversized GSO MSS can be truncated to zero in an active GVE DQO TSO descriptor submitted by the privileged host transmit path, creating a credible guest to host device integrity and availability review candidate without establishing kernel memory corruption or VM escape.
## 6. Manual review recommendation
MANUAL CHECK REQUIRED
Confirm the affected GVE device or firmware response to MSS zero, whether a guest can reliably generate the required GSO metadata, and whether the result is limited to packet loss or can stall a TX queue or the complete interface.
## 7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: gve: DQO: reject TSO packets with an out of range MSS [ Upstream
Commit: 2dc3ae3942e151fef254b7bbb65c832192ad2069
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2dc3ae3942e151fef254b7bbb65c832192ad2069
Changed files:
drivers/net/ethernet/google/gve/gve_desc_dqo.h
drivers/net/ethernet/google/gve/gve_tx_dqo.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=2dc3ae3942e151fef254b7bbb65c832192ad2069
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98556 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98556
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:A/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 5.7
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: 3
Paranoid ActionableScore: 4
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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