From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-64076][MODERATE REGULAR] netfilter: bridge: eb_tables: close module init race [ Upstream Date: Sun, 19 Jul 2026 22:39:31 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-64076 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: 1 X-AL-KERNEL-Commit: c647e2a21bbbaceda6cdb8a44a56f44d231dc4b4 List-Id: CVE: CVE-2026-64076 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: netfilter: bridge: eb_tables: close module init race [ Upstream Commit: c647e2a21bbbaceda6cdb8a44a56f44d231dc4b4 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c647e2a21bbbaceda6cdb8a44a56f44d231dc4b4 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64076 Analysis date: Sun, 19 Jul 2026 22:39:31 -0400 ActionableScore: 3 ActionableScore lower bound: 1 Actionable bucket: Borderline, manual review recommended Manual review required: YES Summary: An ebtables module initialization race exposed sockopts before per-network state was registered, allowing a local CAP_NET_ADMIN-capable process racing module load to plausibly trigger invalid state access and a kernel crash. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64076 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64076 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-2026-64076 MODERATE 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:N/I:N/A:H';CWE-362;CWE-665;**CWE-476;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'ebtables module initialization exposed the nf_register_sockopt interface before the per network ebtables state was registered. A local process racing against module load could reach the ebtables sockopt path while required pernet state is not fully initialized, which can plausibly cause a NULL pointer dereference and kernel crash. For the CVSS the PR:L is used in the paranoid score because some deployments allow less trusted users or containerized workloads to obtain delegated CAP_NET_ADMIN in a network namespace. The issue is not directly network reachable and is triggered through local control plane sockopt operations rather than bridge packet traffic. Impact is denial of service via kernel crash, with no strong evidence of confidentiality or integrity impact from the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 2) YES INIT SIMPLEFIX NETFILTER RACE YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=3 ActionableScoreLower=1 ## 1. ActionableScore * Conservative score: 1 * Paranoid score: 3 * Final recommended bucket: **Borderline, manual review recommended** ## 2. Signal breakdown Conservative signals: * Weak/indirect corruption candidate: +1. The race can expose the ebtables sockopt path before pernet state is registered, plausibly causing invalid or NULL pernet state access. * Reliable kernel crash / strong DoS: +1. The likely failure mode is kernel crash or Oops from using incompletely initialized state. * Broad/default/common subsystem: +1. Netfilter is broadly deployed, although this is ebtables bridge control-plane init rather than the common packet fast path. * Hard or unreliable race / special timing required: -1. The attacker must race a narrow module initialization window. * Requires admin/root/CAP_NET_ADMIN in typical deployments: -2. Practical triggering normally requires local netfilter control privileges and module-load timing. Paranoid adjustment: * Local delegated trigger concern: +1. In some namespace/container setups, delegated CAP_NET_ADMIN or reduced-privilege network administration may make the trigger less than full host-root. * Capability penalty reduced in paranoid view. This is not treated as full host-root if the affected environment gives reduced-capability users access to network namespace administration. ## 3. Reachability analysis The bug is local control-plane reachable through ebtables sockopt operations during module initialization. It is not directly network reachable and is not triggered by bridge packet traffic alone. In typical deployments, modifying ebtables requires CAP_NET_ADMIN and the race also requires timing against module load, which makes reliable exploitation difficult. Namespaces can matter if untrusted users can obtain delegated CAP_NET_ADMIN in a network namespace or can indirectly trigger module loading, but this is deployment-dependent. Call-site confidence: medium. The changed code clearly reorders module initialization so nf_register_sockopt() is last, but the exact downstream dereference path is not shown in the provided patch. ## 4. Severity interpretation This behaves like a borderline Moderate issue, not an Important-class vulnerability. The patch indicates an initialization race with possible invalid state access and DoS, but it does not show attacker-controlled reclaim, write-after-free, type confusion, callback control, arbitrary write, or a practical privilege escalation path. The theoretical concern is incomplete initialization leading to invalid object access, while the realistic impact is local kernel crash under a narrow timing window. ## 5. One-sentence report phrase An ebtables module initialization race exposed sockopts before per-network state was registered, allowing a local CAP_NET_ADMIN-capable process racing module load to plausibly trigger invalid state access and a kernel crash. ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED. This is not strong enough for Important by itself, but it is a race in netfilter initialization with plausible kernel crash behavior and namespace-dependent privilege interpretation, so it should not be blindly auto-closed without confirming product exposure. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: netfilter: bridge: eb_tables: close module init race [ Upstream Commit: c647e2a21bbbaceda6cdb8a44a56f44d231dc4b4 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c647e2a21bbbaceda6cdb8a44a56f44d231dc4b4 Changed files: net/bridge/netfilter/ebtables.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=c647e2a21bbbaceda6cdb8a44a56f44d231dc4b4 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64076 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64076 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:H/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:N/I:N/A:H The Best / paranoid CVSS score: 4.7 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: 1 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).