From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-80905][MODERATE 7.0] net: tap: fix wrong transport_header when sending VLAN-tagged frame [ Upstream Date: Fri, 04 Sep 2026 14:51:53 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-80905 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: 5ffaa5d7f56ab24a8e23cf131eadfef31a3bbc4b List-Id: CVE: CVE-2026-80905 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: net: tap: fix wrong transport_header when sending VLAN-tagged frame [ Upstream Commit: 5ffaa5d7f56ab24a8e23cf131eadfef31a3bbc4b Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5ffaa5d7f56ab24a8e23cf131eadfef31a3bbc4b Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80905 Analysis date: Fri, 04 Sep 2026 14:51:53 -0400 ActionableScore: 5 ActionableScore lower bound: 3 Actionable bucket: Actionable Moderate at minimum Manual review required: NO Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80905 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80905 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-2026-80905 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-80905 CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:L/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: '5.9';DESCR 'A VLAN tagged frame sent through the TAP transmit path can leave skb transport_header unset because skb_probe_transport_header is called after network_header has already been advanced past the VLAN header. The flow dissector then interprets the inner protocol header as a VLAN header, fails to identify the real transport offset, and the skb may continue through dev_queue_xmit with a sentinel transport_header value. For the CVSS the PR:N is used in the paranoid interpretation because a malicious guest or adjacent virtual network peer may be able to provide VLAN tagged frames to an already configured TAP path without host administrative privileges. The issue is not directly Internet reachable in normal deployments because TAP is a local or virtual network device path. Impact is most likely denial of service or incorrect packet metadata handling, with limited integrity impact possible if later packet processing depends on the wrong transport header.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4) YES NETWORK SKB PACKET DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP 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 * Local unprivileged trigger: +1 in the paranoid interpretation. A guest or adjacent virtual network peer may be able to inject VLAN tagged frames into an already configured TAP path without host administrative privileges. * Memory corruption, weak/indirect corruption candidate: +1. The bug leaves skb transport_header at the sentinel value, which is unsafe skb metadata, but the patch does not show UAF, OOB write, object replacement, callback control, or arbitrary write. * Memory layout invariant restoration: +1. The patch restores consistency between skb protocol, network_header, VLAN parsing, flow dissection, and transport_header placement. * Common packet-processing path: +1. TAP is a common virtual networking path and the affected skb metadata may be consumed by later networking code. * Integrity or availability concern: +1. Incorrect transport header metadata can affect later packet processing decisions and may plausibly cause packet handling failure or DoS, although a concrete crash trace is not provided. * Constrained metadata-only primitive: -1 in the conservative view. The demonstrated issue is wrong skb metadata, not a proven attacker-controlled memory overwrite. * Call-site confidence: medium-high. The immediate call to dev_queue_xmit is visible, but the exact downstream consumer of the invalid transport_header is not shown in the supplied patch. 3. Reachability analysis The host-local conservative trigger requires access to a TAP file descriptor or privileges to create and configure TAP, commonly CAP_NET_ADMIN. In virtualization deployments, however, the TAP device may already be configured by a privileged manager and a guest or attached virtual network peer can supply packet contents, including VLAN tagged frames. This makes PR:N defensible for the paranoid interpretation relative to the host, because the attacker may not need host privileges once the virtual network path exists. The issue is not directly Internet reachable in normal deployments and is best modeled as local or adjacent virtual-network reachable. 4. Severity interpretation This is not an Important-class memory corruption issue based on the supplied patch alone. It behaves more like an actionable Moderate networking metadata bug because the affected field is an skb header offset that may be used by later packet-processing code. The theoretical concern is that a sentinel transport_header could become an invalid offset or wrong semantic input to downstream code. The realistic evidence is weaker: the patch demonstrates incorrect VLAN parsing and unset metadata, but not UAF, OOB write, arbitrary write, information disclosure, or a proven privilege escalation path. 5. One-sentence report phrase A VLAN tagged frame on the TAP transmit path can leave skb transport_header unset because flow dissection runs after network_header is advanced past the VLAN header, which may cause incorrect packet metadata handling or DoS in downstream networking code. 6. Manual review recommendation MANUAL CHECK RECOMMENDED. YES REQUIRES MANUAL CHECK. Reason: the conservative score is only borderline, but TAP is common in virtualization and the invalid skb transport_header sentinel may have downstream effects not visible in this small patch. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net: tap: fix wrong transport_header when sending VLAN-tagged frame [ Upstream Commit: 5ffaa5d7f56ab24a8e23cf131eadfef31a3bbc4b Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5ffaa5d7f56ab24a8e23cf131eadfef31a3bbc4b Changed files: drivers/net/tap.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=5ffaa5d7f56ab24a8e23cf131eadfef31a3bbc4b ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80905 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80905 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:H/PR:N/UI:N/S:U/C:N/I:L/A:H The Best / paranoid CVSS score: 5.9 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).