From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-64137][IMPORTANT] smb: client: require net admin for CIFS SWN netlink [ Upstream Date: Sun, 19 Jul 2026 11:59:48 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-64137 X-AL-KERNEL-Priority: IMPORTANT X-AL-KERNEL-Severity: IMPORTANT X-AL-KERNEL-Base-Severity: IMPORTANT X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 7 X-AL-KERNEL-ActionableScore-Lower: 6 X-AL-KERNEL-Commit: 9cf7eb8919344932f909b2fac76296f7656fda8d List-Id: CVE: CVE-2026-64137 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: smb: client: require net admin for CIFS SWN netlink [ Upstream Commit: 9cf7eb8919344932f909b2fac76296f7656fda8d Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9cf7eb8919344932f909b2fac76296f7656fda8d Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64137 Analysis date: Sun, 19 Jul 2026 11:59:48 -0400 ActionableScore: 7 ActionableScore lower bound: 6 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: An unprivileged local process could access the CIFS SWN generic netlink interface to receive sensitive SMB witness registration data including NTLM credentials and inject spoofed witness notifications, causing credential disclosure and possible SMB client state disruption. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64137 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64137 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: IMPORTANT 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-2026-64137 IMPORTANT CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-862;*CWE-200;CWE-284;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:L';BEST CVSS score: '7.8';DESCR 'The CIFS SWN generic netlink interface allowed any local process to send witness notify commands and to subscribe to the SWN multicast group without CAP_NET_ADMIN. This can expose witness registration data and, for NTLM authenticated mounts, SMB username, domain, and password attributes copied from the CIFS session. A local attacker can also inject RESOURCE_CHANGE or CLIENT_MOVE notifications into the in kernel witness handler, which may disrupt SMB client failover behavior or connection state. For the CVSS the PR:L because a local unprivileged process is sufficient to reach the netlink interface, while full administrator privileges are not required. The issue is not directly network reachable and is triggered through a local generic netlink control interface. Impact includes high confidentiality risk from credential disclosure and possible integrity or availability impact for affected SMB client sessions.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) SKIP CVE-2026-64137 UNKNOWN SKIP No affected files built, so skip this CVE NO - - unknown MAYBE DISK SIMPLEFIX SERVERTOCLIENT KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=7 ActionableScoreLower=6 ## 1. ActionableScore * Conservative score: 6 * Paranoid score: 7 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown * Local unprivileged trigger: +1 Any local process could send `CIFS_GENL_CMD_SWN_NOTIFY` and join `CIFS_GENL_MCGRP_SWN` before the fix. * Security-boundary bypass with practical sensitive-object access: +2 The missing `CAP_NET_ADMIN` checks bypass an intended generic-netlink capability boundary. * Sensitive credential theft primitive: +2 Multicast registration messages may include witness registration id and, for NTLM-authenticated mounts, SMB username, domain, and password attributes copied from the CIFS session. * Confidentiality impact plausible: +1 Credential exposure is explicitly described and is the strongest confirmed impact. * Integrity impact plausible: +1 Unprivileged local processes could inject `RESOURCE_CHANGE` or `CLIENT_MOVE` witness notifications into the in-kernel handler. * Availability impact realistic: +1 in paranoid score Spoofed witness notifications may disrupt SMB client failover behavior or connection state. This is plausible but more environment-dependent, so it is counted in the higher score. * Rare or configuration-dependent exposure: -1 in conservative score Practical credential exposure depends on CIFS/SMB client usage, SWN witness functionality, and NTLM-authenticated mounts. No memory corruption, UAF, OOB write, or arbitrary code execution primitive is indicated by the patch. ## 3. Reachability analysis The bug is locally reachable through the CIFS generic-netlink interface. A local unprivileged process can trigger it before the patch, so this is not PR:H in practical terms. It is not directly network-triggerable by a remote host. Namespaces matter because the fix uses `GENL_MCAST_CAP_NET_ADMIN`, requiring `CAP_NET_ADMIN` over the relevant network namespace for multicast group access. The affected path is only relevant when CIFS/SMB client witness support is present and active, but the exposed netlink permission mistake is direct and does not require memory-corruption exploitation. ## 4. Severity interpretation This behaves more like an Important-class access-control and credential-disclosure bug than an ordinary Moderate DoS. The realistic confirmed impact is local disclosure of SMB authentication material from kernel-generated witness registration messages. The notification spoofing path adds plausible integrity and availability impact for SMB client session handling, but without evidence of memory corruption or privilege escalation to kernel code execution. ## 5. One-sentence report phrase An unprivileged local process could access the CIFS SWN generic netlink interface to receive sensitive SMB witness registration data including NTLM credentials and inject spoofed witness notifications, causing credential disclosure and possible SMB client state disruption. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Confirmed local credential disclosure is present, and the affected data may include SMB username, domain, and password attributes. This should not be auto-closed even though the bug is not memory corruption and is not directly network reachable. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: smb: client: require net admin for CIFS SWN netlink [ Upstream Commit: 9cf7eb8919344932f909b2fac76296f7656fda8d Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9cf7eb8919344932f909b2fac76296f7656fda8d Changed files: fs/cifs/netlink.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=9cf7eb8919344932f909b2fac76296f7656fda8d ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64137 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64137 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:H/I:L/A:L The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 7.8 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: 6 Paranoid ActionableScore: 7 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: IMPORTANT KPANIC detected for this report: YES Published priority for this report (same as in Subject): IMPORTANT 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).