From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98554][LOW] vlan: ensure sufficient headroom in vlan_dev_hard_header() [ Upstream Date: Sat, 24 Oct 2026 11:15:16 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98554 X-AL-KERNEL-Priority: LOW X-AL-KERNEL-Severity: LOW X-AL-KERNEL-Base-Severity: LOW X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 2 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 55e007fc3b4d76fa4d6b4660f6904fe6ab045a1b List-Id: CVE: CVE-2026-98554 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: vlan: ensure sufficient headroom in vlan_dev_hard_header() [ Upstream Commit: 55e007fc3b4d76fa4d6b4660f6904fe6ab045a1b Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=55e007fc3b4d76fa4d6b4660f6904fe6ab045a1b Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98554 Analysis date: Sat, 24 Oct 2026 11:15:16 -0400 ActionableScore: 2 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate Manual review required: NO Summary: Insufficient VLAN transmit skb headroom can trigger a checked `skb_under_panic()` and crash the kernel, without evidence of an OOB write or non-crash corruption primitive. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98554 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98554 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-2026-98554 LOW https://www.kernelcve.org/list/?q=CVE-2026-98554 CHECK WITH IMPACT FROM ORIG NN NONE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=LOW RESULT=DIFF TEMP_DISTANCE_MERGE_SKIP=AEGIS_NO_POSITIVE_SEVERITY_EVIDENCE (final 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:N/I:N/A:H';CWE-131;CWE-754;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'vlan_dev_hard_header can call skb_push when an skb lacks enough headroom for the VLAN header and the underlying device header. This can occur with callers such as llc_alloc_frame that reserve ETH_HLEN or less, or with skbs created before VLAN, bonding, team, or device headroom changes. The resulting skb_under_panic can crash the kernel and cause denial of service. For the CVSS the PR:L value reflects that reliable triggering normally requires a local process able to reach the affected transmit or frame construction path, while privileged VLAN configuration may already have been performed by an administrator. Direct triggering by arbitrary remote traffic is not established. The demonstrated primitive is a checked headroom failure and kernel panic, not an OOB write, UAF, information leak, or privilege escalation. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 5.5 and the production ActionableScore returned 2 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were final reconciliation stage LOW to LOW because KP specialist did not establish a qualifying panic and the cross model evidence reconciliation rule was applied. 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 KPANIC_UNSUPPORTED_REMOVED and V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED. The independent weaker Aegis shadow evaluated CVSS 5.5 and ActionableScore 1 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 LOW.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) MAYBE DANGER NOMEMCHK SIMPLEFIX SKB HARDWARE KPANIC_UNSUPPORTED_REMOVED V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 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 base score: 2. * Conservative score: 2; no floor or cap applied. * Raw paranoid score: 2. * Paranoid score: 2; no stronger primitive is technically supported. * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * +1 Reliable kernel crash/strong DoS: insufficient headroom reaches `skb_push()`, whose bounds check invokes `skb_under_panic()`. * +1 Common packet-processing path: the defect is in VLAN transmit header construction. * No OOB-write point: the panic check occurs before the returned header pointer is used for VLAN-header writes. * No B5-R: there is no retry-accumulated index, confirmed heap OOB write, or later consumption of corrupted structured state. * No UAF, controlled overwrite, disclosure, authorization bypass, or integrity primitive is shown. * No extra availability point: it would duplicate the same kernel panic. * No race penalty: concurrent headroom changes are one trigger scenario, but the evidence does not establish difficult or unreliable timing. 3. Reachability analysis A locally generated skb with inadequate reserved headroom can reach the path, including through `llc_alloc_frame()` or after device headroom changes. VLAN/bonding/team configuration may require prior privileged setup, but the evidence does not establish whether the later complete trigger requires host-admin privilege or can be exercised by an ordinary user. The governing capability namespace and full namespace-scoped chain are therefore unknown. Remote traffic reachability is not shown. 4. Primitive and severity reading The demonstrated behavior is a checked skb-headroom underflow leading to `skb_under_panic()`, classified as CLASS_C crash/DoS behavior. The patch proactively expands or copies the skb head with `skb_cow_head()` before pushing headers. It does not demonstrate an actual heap overwrite, corrupted active state, or downstream privileged consumer. Important-candidate preservation rules therefore do not apply, and automatic downgrade remains allowed. 5. One-sentence report phrase Insufficient VLAN transmit skb headroom can trigger a checked `skb_under_panic()` and crash the kernel, without evidence of an OOB write or non-crash corruption primitive. 6. Manual review advice MANUAL CHECK RECOMMENDED Confirm product-specific VLAN configuration and whether an unprivileged local actor can reliably reach the affected frame-construction path. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: vlan: ensure sufficient headroom in vlan_dev_hard_header() [ Upstream Commit: 55e007fc3b4d76fa4d6b4660f6904fe6ab045a1b Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=55e007fc3b4d76fa4d6b4660f6904fe6ab045a1b Changed files: net/8021q/vlan_dev.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=55e007fc3b4d76fa4d6b4660f6904fe6ab045a1b ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98554 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98554 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:H/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: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).