From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-72381][MODERATE 7.0] ksmbd: fix use-after-free of fp->owner.name in durable handle owner check [ Upstream Date: Sun, 16 Aug 2026 05:53:01 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-72381 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: 6 X-AL-KERNEL-ActionableScore-Lower: 4 X-AL-KERNEL-Commit: fb978d72052704c6b06c6b0f129fcd60b77169f5 List-Id: CVE: CVE-2026-72381 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: ksmbd: fix use-after-free of fp->owner.name in durable handle owner check [ Upstream Commit: fb978d72052704c6b06c6b0f129fcd60b77169f5 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fb978d72052704c6b06c6b0f129fcd60b77169f5 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72381 Analysis date: Sun, 16 Aug 2026 05:53:01 -0400 ActionableScore: 6 ActionableScore lower bound: 4 Actionable bucket: Actionable Moderate at minimum Manual review required: YES Summary: A race in ksmbd durable handle reconnect handling allows a remote authenticated SMB client to trigger a use-after-free read of `fp->owner.name` during owner validation, causing at least kernel crash DoS and warranting manual review for possible stale-owner validation impact. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-72381 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72381 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-2026-72381 MODERATE CHECK WITH IMPACT FROM ORIG NN NONE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';*CWE-416;CWE-362;CWE-367;Other CVSS 'AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.4';DESCR 'A use-after-free exists in the ksmbd durable handle reconnect path because ksmbd_vfs_compare_durable_owner() can read fp owner name with strcmp while a concurrent successful reconnect frees the same standalone kstrdup buffer in ksmbd_reopen_durable_fd(). A remote SMB client can trigger the race by issuing concurrent durable reconnect attempts for the same persistent_id, causing strcmp to dereference freed kernel heap memory. For the CVSS the PR:L is used because a remote SMB user normally needs authenticated share access and a valid durable handle context to reach this path, but no local privileges on the server are required. The issue is network reachable over SMB when ksmbd is enabled and exposed to the attacker. Impact is at least denial of service via kernel crash. In the paranoid interpretation, limited confidentiality or integrity impact is possible because the freed owner name is used in an owner validation check, but the patch does not show an arbitrary write primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5) SKIP CVE-2026-72381 UNKNOWN SKIP No affected files built, so skip this CVE NO - - unknown MAYBE REMOTE READ OOB LOCK DANGER DISK RACE UAF SKIP KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=6 ActionableScoreLower=4 ## 1. ActionableScore * Conservative score: **4** * Paranoid score: **6** * Final recommended bucket: **Actionable Moderate at minimum** ## 2. Signal breakdown Conservative signals: * **Remote reachable / network-triggerable: +2** The affected path is in ksmbd SMB2 durable reconnect handling and can be reached by a remote SMB client when ksmbd is enabled and exposed. * **Memory corruption, weak primitive: +1** This is a confirmed slab use-after-free, but the observed access is a `strcmp()` read of a freed `kstrdup()` buffer. No write-after-free, callback dispatch, type confusion, or arbitrary write is shown. * **Real lifetime corruption: +1** `fp->owner.name` has a lifetime independent of the `fp` refcount, and one reconnect path can free it while another path reads it. * **Reliable kernel crash / strong DoS: +1** KASAN reports slab-use-after-free in `strcmp()`. In production this can plausibly become an Oops or kernel crash. * **Hard or unreliable race / special timing required: -1** Triggering requires concurrent SMB2 durable reconnects for the same `persistent_id`, so timing and session state matter. Paranoid additional signals: * **Confidentiality impact plausible: +1** The freed string is used in an owner validation check. If reuse is attacker-influenced, stale reads could theoretically affect authorization-sensitive comparison behavior, although this is not demonstrated. * **Integrity impact plausible: +1** Same reasoning as above. The validation check protects durable handle ownership, so a stale owner-name comparison is security-relevant. However, there is no demonstrated write primitive or controlled object replacement. Not awarded: * **Strong LPE plausibility: +0** No attacker-controlled reclaim, callback control, arbitrary write, refcount takeover, or type confusion is shown. * **Generic strong memory corruption: +0** This is a race-dependent UAF read, not a demonstrated strong corruption primitive. * **Broad/default/common subsystem: +0** ksmbd is network-facing when enabled, but it is not a universal default core networking path. ## 3. Reachability analysis A remote SMB client can potentially trigger the bug by racing two SMB2 durable reconnect operations on the same `persistent_id`. In realistic deployments the attacker likely needs authenticated SMB access, a valid durable handle context, and the ability to issue concurrent reconnect attempts. This supports **PR:L** in CVSS-style reasoning rather than PR:N. Namespaces and containers do not materially lower the requirement unless a containerized or delegated environment exposes authenticated SMB access to untrusted users. The path is not triggered by ordinary packet traffic alone. It requires ksmbd to be enabled, reachable over the network, and configured with durable handle behavior in use. Call-site confidence: **high**, because the patch and stack trace show the concrete call path: `smb2_open -> smb2_check_durable_oplock -> ksmbd_vfs_compare_durable_owner -> strcmp`. ## 4. Severity interpretation This is stronger than an ordinary Moderate because it is a **network-reachable authenticated race UAF** in a kernel SMB server. The conservative view treats it mainly as remote authenticated DoS due to a freed pointer read in `strcmp()`. The paranoid view raises the score because the stale read occurs in an owner validation path, which is more security-sensitive than a generic crash-only dereference. However, the patch does not show a controlled reclaim primitive, writable stale object access, type confusion, or arbitrary write, so this should not be treated as a strong Important-class memory-corruption exploit without manual confirmation. ## 5. One-sentence report phrase A race in ksmbd durable handle reconnect handling allows a remote authenticated SMB client to trigger a use-after-free read of `fp->owner.name` during owner validation, causing at least kernel crash DoS and warranting manual review for possible stale-owner validation impact. ## 6. Manual review recommendation **MANUAL CHECK REQUIRED** Reason: this is a network-reachable race-based use-after-free in ksmbd, with a confirmed KASAN UAF and a security-relevant owner validation call path. Conservative impact is DoS, but the owner-check context makes it unsafe to auto-close without manual analysis. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: ksmbd: fix use-after-free of fp->owner.name in durable handle owner check [ Upstream Commit: fb978d72052704c6b06c6b0f129fcd60b77169f5 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fb978d72052704c6b06c6b0f129fcd60b77169f5 Changed files: fs/smb/server/vfs_cache.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=fb978d72052704c6b06c6b0f129fcd60b77169f5 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-72381 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72381 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:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS score: 6.4 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: 6 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).