From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98954][MODERATE REGULAR] net: always dissect GSO packets in __virtio_net_hdr_to_skb() [ Upstream Date: Mon, 26 Oct 2026 16:09:22 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98954 X-AL-KERNEL-Priority: MODERATE REGULAR X-AL-KERNEL-Severity: MODERATE REGULAR X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 3 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 5f4dfdf0077730e9d3ef5b37ceb17a5a56d6f34c List-Id: CVE: CVE-2026-98954 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: net: always dissect GSO packets in __virtio_net_hdr_to_skb() [ Upstream Commit: 5f4dfdf0077730e9d3ef5b37ceb17a5a56d6f34c Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5f4dfdf0077730e9d3ef5b37ceb17a5a56d6f34c Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98954 Analysis date: Mon, 26 Oct 2026 16:09:22 -0400 ActionableScore: 3 ActionableScore lower bound: unknown Actionable bucket: Borderline / manual review recommended Manual review required: YES Summary: Untrusted virtio GSO metadata can bypass transport-header validation and cause a later two-byte slab OOB read and kernel crash. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98954 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98954 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-2026-98954 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98954 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 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:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H';CWE-125;*CWE-20;CWE-1285;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.1';DESCR 'Untrusted GSO validation could be bypassed because skb network_header was treated as a boolean even though zero is a valid initialized offset. Malformed packets, IPv4 options, or IPv6 extension headers could leave skb transport_header at 0xffff or leave the TCP header outside linear skb data. A later tcp_hdrlen call performs a confirmed slab out of bounds read and can cause a kernel crash. For the CVSS the PR:L value reflects that reliable triggering normally requires access to a TUN or TAP file descriptor or control of an equivalent virtio or UML packet source. The issue is not established as generally remote network reachable because ordinary packet delivery alone does not prove control of the required virtio GSO metadata. Availability impact is high. Confidentiality impact is limited only in the paranoid vector because the primitive is an out of bounds read without a demonstrated path for returning kernel data. Integrity impact is not supported because no out of bounds write, UAF, or arbitrary write is shown. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 6.1 and the production ActionableScore returned 3 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were ActionableScore thresholds stage MODERATE_KPANIC to MODERATE because the ActionableScore threshold rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and V41_INHERITED_KPANIC_PROMOTION_BLOCKED and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 3.3 and ActionableScore 2 with primitive class CLASS_C and manual review REQUIRED. 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 Borderline / manual review recommended (with actual score 3) MAYBE READ KASAN OOB SKB HARDWARE QDISC IPV6 PACKET DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 V41_INHERITED_KPANIC_PROMOTION_BLOCKED MANUAL_REVIEW_REQUIRED - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=3 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES RequiresHostUID0=NO AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw base score: 3. * Conservative score: 3; no floor or cap applied. * Raw paranoid score: 3. * Paranoid score: 3; confidentiality is not scored without a disclosure path. * Final recommended bucket: **Borderline / manual review recommended**:: 2. Signal breakdown * +1 limited slab out-of-bounds read: malformed GSO state leaves `transport_header` at `0xffff` or outside linear data, and `tcp_hdrlen()` reads two bytes out of bounds. * +1 reliable kernel crash/strong DoS: the supplied KASAN trace reaches the invalid read through `skb_gso_transport_seglen()` and qdisc enqueue. * +1 local below-host-admin trigger: supplied evidence grounds triggering through access to a TUN/TAP descriptor or equivalent untrusted virtio packet source. * +1 common packet-processing path: corrupted header state reaches GSO validation and qdisc processing. * -1 delegated-resource prerequisite: triggering requires control of a suitable TUN/TAP descriptor or equivalent packet source rather than ordinary local packet transmission. * No extra availability point: it would duplicate the same crash. * No confidentiality point: adjacent bytes influence an internal length read, but no return or disclosure path is shown. * No write, UAF, checksum-header write, controlled state corruption, arbitrary access, or integrity effect is shown. * B5-R does not apply: this is not an accumulated retry-driven OOB write. * B3-PENDING and B4-PENDING do not apply: there is neither a shared-backing write nor an authorization decision bypass. 3. Reachability analysis A local actor with access to an existing TUN/TAP file descriptor can provide packet bytes and virtio GSO metadata without effective host-administrator powers or host UID 0. Descriptor creation or delegation may require prior privileged setup, but the later data-plane trigger does not. No namespace capability is required for the delegated-FD path. Ordinary remote traffic is not sufficient because it does not normally control virtio GSO metadata. No special hardware or difficult race is required. 4. Primitive and severity reading The exact primitive is a two-byte slab OOB read caused by incomplete GSO dissection and an invalid or non-linear transport-header location. It is not a lifetime violation or write primitive. The demonstrated consequence is a kernel fault/DoS; disclosure, policy change, LPE, and persistent integrity impact remain unsupported. This is CLASS_C, not an Important-preserving Class B chain. Auto-downgrade remains allowed, although manual review is recommended due to the confirmed OOB access and multiple untrusted packet-source callers. 5. One-sentence report phrase Untrusted virtio GSO metadata can bypass transport-header validation and cause a later two-byte slab OOB read and kernel crash. 6. Manual review advice MANUAL CHECK RECOMMENDED Confirm product-specific TUN/TAP or guest virtio descriptor exposure and crash reproducibility. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net: always dissect GSO packets in __virtio_net_hdr_to_skb() [ Upstream Commit: 5f4dfdf0077730e9d3ef5b37ceb17a5a56d6f34c Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5f4dfdf0077730e9d3ef5b37ceb17a5a56d6f34c Changed files: net/core/gso.c net/sched/sch_tbf.c net/core/dev.c arch/um/drivers/vector_transports.c drivers/net/tun.c drivers/net/virtio_net.c include/linux/virtio_net.h 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=5f4dfdf0077730e9d3ef5b37ceb17a5a56d6f34c ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98954 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98954 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:H The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H The Best / paranoid CVSS score: 6.1 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: 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).