From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-64382][IMPORTANT] smb: client: fix double-free in SMB2_open() replay Date: Sat, 25 Jul 2026 14:33:58 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-64382 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: 8 X-AL-KERNEL-ActionableScore-Lower: 6 X-AL-KERNEL-Commit: 02bc2896bdc3e29362d6e40d404006944a159c25 List-Id: CVE: CVE-2026-64382 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: smb: client: fix double-free in SMB2_open() replay Commit: 02bc2896bdc3e29362d6e40d404006944a159c25 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=02bc2896bdc3e29362d6e40d404006944a159c25 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64382 Analysis date: Sat, 25 Jul 2026 14:33:58 -0400 ActionableScore: 8 ActionableScore lower bound: 6 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A stale response-buffer state in the SMB2_open() replay path can cause a double-free when a malicious SMB server returns a replayable error and the next replay attempt fails before initializing a new response, leading to kernel memory corruption and at least a remote DoS risk. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64382 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64382 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-2026-64382 IMPORTANT CHECK WITH IMPACT FROM ORIG NN MODERATE 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-415;*CWE-672;*CWE-416;Other CVSS 'AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:H';BEST CVSS score: '8.1';DESCR 'A double-free can occur in the SMB client SMB2_open() replay path because response buffer bookkeeping from a previous response-bearing attempt may remain valid after that buffer was already freed. A malicious or compromised SMB server can influence the client by returning a replayable error and causing the next replay attempt to fail before a new response buffer is initialized. For the CVSS the PR:N is used because the attacker does not need local privileges on the victim system when acting as the SMB server or controlling the network path. The base score uses UI:R because a victim client normally needs to connect to or access the SMB share. The paranoid score uses UI:N for already mounted or automatically accessed SMB shares where the server can trigger the condition without new user action. Impact is at least denial of service via kernel crash. In the worst case, the double-free memory corruption may allow confidentiality or integrity impact and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8) YES DANGER DISK UAF SERVERTOCLIENT KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=8 ActionableScoreLower=6 ## 1. ActionableScore * Conservative score: 6 * Paranoid score: 8 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative signals: * Remote reachable / network-triggerable: +2. A malicious or compromised SMB server can influence the SMB client replay path after the client connects or has an active mount. * Memory corruption, strong corruption primitive: +2. The commit explicitly describes a double-free of a response buffer. * Real lifetime corruption: +1. The bug is stale response-buffer bookkeeping leading to freeing an already freed buffer. * Reliable kernel crash / strong DoS: +1. Double-free in kernel client code is a realistic crash condition. * Important filesystem/storage path: +1. SMB client is a network filesystem path used for file access. * Hard or unreliable sequence required: -1. Triggering requires a replayable error and SMB2_open_init() failure before the next send. Paranoid additional signals: * Weak LPE concern: +1. Kernel heap double-free can be a possible exploitation primitive, although no controlled reclaim or overwrite is shown in the patch. * Broad/common subsystem exposure: +1. SMB/CIFS clients are commonly deployed in enterprise and storage environments. Not counted conservatively: * Confidentiality and integrity impact are not counted in the lower score because the patch does not show a concrete info leak, arbitrary write, controlled reclaim, or object replacement primitive. * Availability is not double-counted beyond the strong DoS signal. ## 3. Reachability analysis The realistic attacker is a malicious SMB server, compromised SMB server, or network attacker able to influence the SMB session. A victim client normally must connect to or already have mounted the SMB share, so practical exposure depends on SMB client use and automount or application access patterns. No local privileges on the victim are required for the server-side attacker model. Containers and namespaces do not materially reduce the remote server influence if the host kernel SMB client performs the mount or file access. The path is not universally default-enabled, but SMB client usage is common enough that this should not be treated as a rare subsystem. Call-site confidence: medium. The patch context clearly shows SMB2_open() replay cleanup state, but the full cleanup/free call path is not included in the provided diff. ## 4. Severity interpretation This is stronger than ordinary Moderate because it is network-influenced kernel memory corruption in a filesystem client. The conservative interpretation is Actionable Moderate because the demonstrated impact is primarily a kernel crash and the trigger sequence is specific. The paranoid interpretation is Strong Important candidate because double-free bugs can sometimes become exploitable beyond DoS, especially in kernel heap contexts, even though this patch does not prove a reliable privilege escalation primitive. ## 5. One-sentence report phrase A stale response-buffer state in the SMB2_open() replay path can cause a double-free when a malicious SMB server returns a replayable error and the next replay attempt fails before initializing a new response, leading to kernel memory corruption and at least a remote DoS risk. ## 6. Manual review recommendation MANUAL CHECK REQUIRED This is network-influenced kernel double-free memory corruption in the SMB client. Even though the reliable demonstrated impact is DoS, the bug class and remote server control make it unsuitable for auto-closure. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: smb: client: fix double-free in SMB2_open() replay Commit: 02bc2896bdc3e29362d6e40d404006944a159c25 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=02bc2896bdc3e29362d6e40d404006944a159c25 Commit description: A response-bearing attempt can return a replayable error and free its response buffer. If SMB2_open_init() fails before the next send, cleanup retains the previous buffer type and frees that response again. Reset response bookkeeping before each attempt to prevent the stale free. Fixes: 4f1fffa ("cifs: commands that are retried should have replay flag set") Cc: stable@vger.kernel.org Signed-off-by: Henrique Carvalho Signed-off-by: Steve French Signed-off-by: Greg Kroah-Hartman Changed files: fs/smb/client/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=02bc2896bdc3e29362d6e40d404006944a159c25 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64382 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64382 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:R/S:U/C:L/I:L/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: 6 Paranoid ActionableScore: 8 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).