From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-80906][MODERATE 7.0] net: packet: fix wrong transport_header when sending VLAN-tagged frame [ Upstream Date: Fri, 04 Sep 2026 14:20:47 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-80906 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 5 X-AL-KERNEL-ActionableScore-Lower: 3 X-AL-KERNEL-Commit: a4b82de96d465ddb44bc931145c0fa80c4fe9c9c List-Id: CVE: CVE-2026-80906 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: net: packet: fix wrong transport_header when sending VLAN-tagged frame [ Upstream Commit: a4b82de96d465ddb44bc931145c0fa80c4fe9c9c Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a4b82de96d465ddb44bc931145c0fa80c4fe9c9c Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80906 Analysis date: Fri, 04 Sep 2026 14:20:47 -0400 ActionableScore: 5 ActionableScore lower bound: 3 Actionable bucket: Actionable Moderate at minimum Manual review required: NO Summary: AF_PACKET can leave `skb->transport_header` unset for VLAN tagged SOCK_RAW GSO frames due to inconsistent VLAN header parsing order, allowing a local CAP_NET_RAW capable process to potentially trigger packet processing failure or a kernel crash. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80906 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80906 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: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-80906 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-80906 CHECK WITH IMPACT FROM ORIG NN LOW 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-665;CWE-682;*CWE-20;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'AF_PACKET can leave skb transport_header unset for VLAN tagged SOCK_RAW GSO frames because skb_probe_transport_header runs after skb_set_network_header moves network_header past the VLAN header while skb protocol still names the outer VLAN EtherType. The flow dissector then reads the inner protocol header as a VLAN header, fails to identify the transport protocol, and leaves the transport header at the unset sentinel value. For the CVSS the PR:L is used because triggering requires a local process with permission to create AF_PACKET raw sockets, usually CAP_NET_RAW or an equivalent delegated capability. The issue is not directly network reachable because the attacker must inject frames through a local packet socket on the target. Impact is primarily denial of service or packet processing failure, and the paranoid score treats later use of the unset transport header by networking offload or checksum paths as a plausible kernel crash risk.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4) YES REMOTE SKB PACKET DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=3 ## 1. ActionableScore * Conservative score: 3 * Paranoid score: 5 * Final recommended bucket: **Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative signals: * Weak or indirect corruption candidate: +1 `transport_header` can remain at the unset sentinel value `~0U`, which may later be consumed as an skb header offset. This is not a proven arbitrary write or UAF, but it is more than pure bookkeeping. * Memory layout invariant restoration: +1 The patch restores consistency between `skb->protocol`, `network_header`, VLAN depth, and `transport_header` inside skb header parsing. * Common networking packet path: +1 The bug is in `net/packet/af_packet.c` and affects AF_PACKET skb construction for VLAN tagged SOCK_RAW GSO frames. * Requires CAP_NET_RAW or equivalent in typical deployments: -1 Reliable triggering normally requires a local process able to create AF_PACKET raw sockets. Paranoid additional signals: * Local trigger may be reachable from reduced privilege contexts: +1 In systems with delegated `CAP_NET_RAW`, containers, or permissive user namespace setups, this may be reachable without full host root. * Reliable kernel crash / strong DoS concern: +1 The unset sentinel `transport_header` may be dangerous if later used by GSO, checksum, or offload paths as a valid header offset. Not awarded: * No remote reachable signal. The attacker must inject through a local packet socket. * No strong memory corruption signal. The patch does not show UAF, OOB write, double free, type confusion, or attacker controlled overwrite. * No confidentiality or integrity impact. No leak or write primitive is demonstrated. ## 3. Reachability analysis The likely trigger is a local process sending VLAN tagged frames through AF_PACKET SOCK_RAW with GSO related behavior. In normal host deployments this requires `CAP_NET_RAW`, so it is not a pure unprivileged local bug by default. However, `CAP_NET_RAW` is sometimes delegated to containers or service contexts, and user namespace configurations can change practical reachability. The path is not directly network reachable from incoming traffic. The bug is in local packet socket transmit side parsing and skb header setup, not in a remote protocol receive parser. The affected subsystem is common kernel networking code, but the exact trigger requires VLAN tagged AF_PACKET SOCK_RAW GSO frames. Call-site confidence: medium. The patch clearly shows the wrong ordering and unset `transport_header` condition, but the supplied context does not show the later consumers that would turn the sentinel into a concrete crash. ## 4. Severity interpretation This is not an Important-class vulnerability based on the supplied patch alone. It behaves more like an actionable Moderate issue because it affects skb header invariants in a common networking subsystem and can plausibly lead to a kernel crash if the unset transport header is later consumed. The theoretical concern is invalid skb offset use after parser disagreement. The realistic evidence supports DoS or packet processing failure, not privilege escalation or information disclosure. ## 5. One-sentence report phrase AF_PACKET can leave `skb->transport_header` unset for VLAN tagged SOCK_RAW GSO frames due to inconsistent VLAN header parsing order, allowing a local CAP_NET_RAW capable process to potentially trigger packet processing failure or a kernel crash. ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED. YES REQUIRES MANUAL CHECK Reason: the conservative score is only borderline, but the paranoid score reaches actionable Moderate because skb header offset invariants are security sensitive and later networking offload or checksum paths may turn the unset sentinel into a real crash. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net: packet: fix wrong transport_header when sending VLAN-tagged frame [ Upstream Commit: a4b82de96d465ddb44bc931145c0fa80c4fe9c9c Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a4b82de96d465ddb44bc931145c0fa80c4fe9c9c Changed files: net/packet/af_packet.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=a4b82de96d465ddb44bc931145c0fa80c4fe9c9c ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80906 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80906 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: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: 3 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: NO 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).