From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-31678][MODERATE 7.0] openvswitch: defer tunnel netdev_put to RCU release [ Upstream Date: Thu, 03 Sep 2026 09:01:59 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-31678 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 5 X-AL-KERNEL-ActionableScore-Lower: 4 X-AL-KERNEL-Commit: 9d56aced21fb9c104e8a3f3be9b21fbafe448ffc List-Id: CVE: CVE-2026-31678 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: openvswitch: defer tunnel netdev_put to RCU release [ Upstream Commit: 9d56aced21fb9c104e8a3f3be9b21fbafe448ffc Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9d56aced21fb9c104e8a3f3be9b21fbafe448ffc Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-31678 Analysis date: Thu, 03 Sep 2026 09:01:59 -0400 ActionableScore: 5 ActionableScore lower bound: 4 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: Open vSwitch tunnel vport destruction could drop a netdev reference before the RCU release path while concurrent readers still observe vport dev, creating a stale pointer UAF candidate that can cause local kernel DoS and warrants manual review. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-31678 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-31678 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: YES A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-31678 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-31678 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'Open vSwitch tunnel vport destruction can drop the netdev reference before the RCU release path while concurrent readers may still observe vport dev. This creates a race in object lifetime management and can lead to a use-after-free candidate or kernel crash when stale readers access the net_device after the reference was released. For the CVSS the PR:L is used because reliable triggering typically requires a local process with CAP_NET_ADMIN or delegated network administration rights to create or destroy OVS tunnel vports, but not full host root control in all deployments. The issue is not directly network reachable as a packet only attack and is primarily triggered through local control plane operations on OVS devices. Impact is at least local denial of service via kernel crash and in the paranoid interpretation may include confidentiality or integrity impact due to the UAF style lifetime race. YES REQUIRES MANUAL CHECK.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5) MAYBE DANGER RACE HARDWARE LINUS KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP - - guess ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=4 ## 1. ActionableScore * Conservative score: 4 * Paranoid score: 5 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown * Memory corruption, Weak/indirect corruption candidate: +1 The patch and commit describe a race where concurrent readers may still observe `vport->dev` after `netdev_put()` drops the reference. This is a stale pointer / UAF candidate, but no controlled reclaim, overwrite, callback dispatch, or type confusion is shown. * Real lifetime corruption: +1 This is directly an object lifetime bug involving `net_device`, `vport->dev`, and RCU delayed release. * Reliable kernel crash / strong DoS: +1 A stale `net_device` pointer observed by RCU readers can plausibly cause kernel crash or invalid memory access. The primary realistic impact is DoS. * Broad networking / virtualization exposure: +1 Open vSwitch is common in virtualization, container networking, and cloud networking stacks, even though it is not a default path on all Linux systems. * Hard or unreliable race / special timing required: -1 in conservative scoring The issue depends on a race between tunnel vport destruction, netdev unregister, and concurrent RCU readers. * CAP_NET_ADMIN / privileged control plane requirement: not applied as full -2 in paranoid scoring Creating or destroying OVS tunnel vports normally requires CAP_NET_ADMIN, but this capability is often delegated to containers, network services, or reduced privilege control-plane processes. This is not equivalent to full host root in all deployments. ## 3. Reachability analysis The bug is triggered through local OVS control-plane operations that destroy tunnel vports while concurrent readers can still observe `vport->dev`. It is not directly network reachable as a packet-only attack. Reliable triggering normally requires CAP_NET_ADMIN or equivalent delegated network administration rights. Namespaces and containers matter. If OVS management is exposed to a container root, network namespace manager, SDN agent, or service account with delegated network privileges, the practical privilege requirement is closer to local low-privileged or reduced-privileged control-plane access than full host root. The affected path is not universally default-enabled, but OVS is common in virtualized and cloud deployments. ## 4. Severity interpretation This is not a pure correctness or warning-only fix. The patch explicitly moves `netdev_put()` to the RCU free path to prevent readers from observing a prematurely released `net_device`, which is a real lifetime safety issue. Realistically, this behaves like an actionable Moderate local DoS with a UAF-style lifetime race. Theoretical escalation is not demonstrated because the patch does not show attacker-controlled reclaim, type confusion, writable stale object access, or callback control. However, because it is an RCU lifetime UAF candidate in a networking subsystem, it should not be auto-closed without manual review. ## 5. One-sentence report phrase Open vSwitch tunnel vport destruction could drop a netdev reference before the RCU release path while concurrent readers still observe vport dev, creating a stale pointer UAF candidate that can cause local kernel DoS and warrants manual review. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: this is an RCU object lifetime race with a plausible UAF condition in a networking subsystem. No strong LPE primitive is demonstrated, but the bug class and patch context are sufficient to require manual review rather than automatic closure. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: openvswitch: defer tunnel netdev_put to RCU release [ Upstream Commit: 9d56aced21fb9c104e8a3f3be9b21fbafe448ffc Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9d56aced21fb9c104e8a3f3be9b21fbafe448ffc Changed files: net/openvswitch/vport-netdev.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=9d56aced21fb9c104e8a3f3be9b21fbafe448ffc ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-31678 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-31678 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:H/PR:L/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 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: 4 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: YES 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).