From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-72422][MODERATE 7.0] ksmbd: fix use-after-free of conn->preauth_info in concurrent SMB2 NEGOTIATE [ Upstream Date: Sat, 15 Aug 2026 03:18:43 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-72422 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: c7bef84740d1d57848c74f6f5b996606e43ea4fe List-Id: CVE: CVE-2026-72422 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: ksmbd: fix use-after-free of conn->preauth_info in concurrent SMB2 NEGOTIATE [ Upstream Commit: c7bef84740d1d57848c74f6f5b996606e43ea4fe Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c7bef84740d1d57848c74f6f5b996606e43ea4fe Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72422 Analysis date: Sat, 15 Aug 2026 03:18:43 -0400 ActionableScore: 5 ActionableScore lower bound: 4 Actionable bucket: Actionable Moderate at minimum Manual review required: YES Summary: A remote unauthenticated SMB client may trigger a race in ksmbd SMB2 NEGOTIATE handling where `conn->preauth_info` is freed by one worker and read by another, causing a slab use-after-free read and kernel crash. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-72422 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72422 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-2026-72422 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:N/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '8.1';DESCR 'A use-after-free in the ksmbd SMB2 NEGOTIATE response path occurs because conn preauth_info can be freed by one worker while another worker reads conn preauth_info Preauth_HashValue without holding the connection lock. A remote client can trigger the race by driving concurrent SMB2 NEGOTIATE requests on the same connection, causing a slab use-after-free read and a kernel crash. For the CVSS the PR:N is used because SMB2 NEGOTIATE is processed before session authentication and the attacker only needs network reachability to the ksmbd service. The issue is network reachable over SMB and is most relevant when ksmbd is exposed to untrusted clients or reachable from a local or internal network. Impact is at least remote denial of service via kernel crash. In the paranoid score, the network reachable kernel heap UAF is treated as possible confidentiality and integrity impact and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5) SKIP CVE-2026-72422 UNKNOWN SKIP No affected files built, so skip this CVE NO - - unknown MAYBE REMOTE DISK RACE LEAK UAF SKIP KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=4 ## 1. ActionableScore * Conservative score: 4 * Paranoid score: 5 * Final recommended bucket: **Actionable Moderate at minimum**:: ## 2. Signal breakdown * Remote reachable / network-triggerable: +2 SMB2 NEGOTIATE is reachable over the ksmbd SMB service before session authentication. * Memory corruption, weak/indirect corruption candidate: +1 This is a KASAN-confirmed slab use-after-free read, but the patch does not show attacker-controlled reclaim, overwrite, callback control, type confusion, or refcount takeover. * Real lifetime corruption: +1 `conn->preauth_info` can be freed by one worker while another worker dereferences it without holding `ksmbd_conn_lock`. * Reliable kernel crash / strong DoS: +1 The confirmed consequence is a kernel UAF read that can crash the system. * Hard or unreliable race / special timing required: -1 in conservative score Triggering requires concurrent SMB2 NEGOTIATE handling on the same connection. The paranoid score does not subtract this because the race is directly described and remotely driveable by request concurrency. * Race-UAF downgrade rule applied No LPE bonus, no confidentiality bonus, and no integrity bonus are counted for the conservative score because the patch only demonstrates stale read after free, not controlled reuse or write-after-free. ## 3. Reachability analysis A remote unauthenticated client can potentially trigger the bug if the ksmbd service is enabled and reachable. The affected path is SMB2 NEGOTIATE, which occurs before authenticated session setup, so no SMB credentials are required. Namespaces and containers do not materially reduce the remote exposure once the host ksmbd listener is reachable. The subsystem is not universally enabled by default on all Linux systems, but it is realistic in NAS, appliance, file-server, and embedded SMB deployments. Call-site confidence: high. The commit message and patch show the allocation/free side, the unlocked send-path read, and the locking fix at the dereference site. ## 4. Severity interpretation This is more than an ordinary Moderate because it is a network-reachable pre-authentication kernel lifetime bug with confirmed UAF behavior. Realistically, the demonstrated impact is remote denial of service through a kernel crash. Theoretical escalation beyond DoS is not proven by the patch because there is no demonstrated attacker-controlled reclaim, write primitive, object replacement, or callback dispatch. For triage, the issue should remain actionable due to remote pre-auth reachability and kernel heap UAF semantics. ## 5. One-sentence report phrase A remote unauthenticated SMB client may trigger a race in ksmbd SMB2 NEGOTIATE handling where `conn->preauth_info` is freed by one worker and read by another, causing a slab use-after-free read and kernel crash. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: network-reachable pre-auth kernel UAF with confirmed KASAN evidence should not be auto-closed, even though the currently supported practical impact is DoS rather than proven privilege escalation. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: ksmbd: fix use-after-free of conn->preauth_info in concurrent SMB2 NEGOTIATE [ Upstream Commit: c7bef84740d1d57848c74f6f5b996606e43ea4fe Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c7bef84740d1d57848c74f6f5b996606e43ea4fe Changed files: fs/ksmbd/smb2pdu.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=c7bef84740d1d57848c74f6f5b996606e43ea4fe ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-72422 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72422 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:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 8.1 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).