From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-64534][IMPORTANT] nvmet-tcp: check INIT_FAILED before nvmet_req_uninit in digest error path Date: Mon, 27 Jul 2026 02:51:05 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-64534 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: 22ec7a9fe9153d2737ee9b2fa6d2e43a1491decf List-Id: CVE: CVE-2026-64534 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: nvmet-tcp: check INIT_FAILED before nvmet_req_uninit in digest error path Commit: 22ec7a9fe9153d2737ee9b2fa6d2e43a1491decf Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=22ec7a9fe9153d2737ee9b2fa6d2e43a1491decf Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64534 Analysis date: Mon, 27 Jul 2026 02:51:05 -0400 ActionableScore: 8 ActionableScore lower bound: 6 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A network-reachable refcount lifetime bug in the NVMe/TCP target data digest error path can call `nvmet_req_uninit()` on an INIT_FAILED request, causing refcount underflow, UAF diagnostics, and a persistent workqueue deadlock. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64534 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64534 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-2026-64534 IMPORTANT CHECK WITH IMPACT FROM ORIG NN IMPORTANT Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';CWE-911;*CWE-416;CWE-703;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.5';DESCR 'A refcount underflow in the NVMe/TCP target digest error path can occur because nvmet_req_uninit may be called for a request whose initialization had already failed. When the command is in the INIT_FAILED state, the matching percpu_ref_tryget_live was not performed, so the later percpu_ref_put can underflow the reference counter and produce UAF diagnostics followed by a permanent workqueue deadlock. For the CVSS the PR:N is used because a remote host does not need a local account on the target and only needs reachability to the exposed NVMe/TCP target path. The issue is treated as AV:A because NVMe/TCP targets are typically deployed on isolated storage or data center networks rather than the public Internet. Impact is at least denial of service via target side deadlock or kernel failure. For the paranoid score, the refcount underflow and UAF diagnostic make memory corruption impact plausible enough for manual review sensitivity.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8) YES REMOTE OOB DEADLOCK INIT NVME ERRORPATH UAF NETWORK LINUS KPANIC NO NO guess ====================================================================== 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** The affected path is in the NVMe/TCP target receive path. A remote NVMe/TCP host that can reach the target can influence the digest error path. * **Memory corruption, weak/indirect corruption candidate: +1** The bug causes a refcount underflow and UAF diagnostic, but the patch does not demonstrate attacker-controlled reclaim, object replacement, or arbitrary write. * **Real lifetime corruption: +1** The issue is an unmatched `percpu_ref_put()` after failed request initialization, i.e. a real refcount/lifetime imbalance. * **Reliable kernel crash / strong DoS: +1** The commit describes WARNING, UAF diagnostic, and eventually a permanent workqueue deadlock. * **Important filesystem/storage path: +1** NVMe/TCP target is a storage transport path and failures can affect remote storage service availability. * **Hard or special condition required: -1** Triggering requires the INIT_FAILED request state plus a data digest mismatch path. Paranoid additional/elevated signals: * **Memory corruption, strong corruption primitive: +2 instead of weak +1** For paranoid triage, refcount underflow plus UAF diagnostic is treated as a stronger memory-safety signal. * **Weak LPE concern: +1** No concrete LPE primitive is shown, but refcount lifetime misuse in a network-reachable kernel path is enough to require manual review. * **Availability impact realistic: +1** The described deadlock is persistent rather than a transient per-connection failure. ## 3. Reachability analysis A remote host with access to the NVMe/TCP target endpoint can plausibly trigger the affected receive path by causing a digest mismatch while the command is in an initialization-failed state. No local account on the target is required, so PR:N is reasonable for CVSS-style reasoning. This is not usually Internet-exposed. NVMe/TCP targets are typically deployed in storage or data-center networks, so exposure depends on whether untrusted hosts can reach that storage fabric. Namespaces and containers do not materially reduce the attacker requirement on the target side, because the trigger is protocol-level access to the target listener. The path is not default-enabled on every Linux system, but it is relevant on systems configured as NVMe/TCP targets with digest handling. ## 4. Severity interpretation This is above ordinary Moderate because it is network-triggerable in a kernel storage target and involves a concrete refcount lifetime bug, not just validation cleanup. Realistically demonstrated impact is strong DoS via warning/UAF diagnostic and permanent workqueue deadlock. Theoretical memory corruption risk is higher than a plain NULL dereference because an unmatched `percpu_ref_put()` can corrupt lifetime accounting, but the patch does not show a controlled reclaim, arbitrary write, or reliable privilege escalation primitive. Conservative handling: **Actionable Moderate**. Paranoid handling: **Strong Important candidate**, mainly due to network reachability plus refcount underflow/UAF diagnostics. ## 5. One-sentence report phrase A network-reachable refcount lifetime bug in the NVMe/TCP target data digest error path can call `nvmet_req_uninit()` on an INIT_FAILED request, causing refcount underflow, UAF diagnostics, and a persistent workqueue deadlock. ## 6. Manual review recommendation **MANUAL CHECK REQUIRED** Reason: the issue is reachable through a remote storage protocol path and involves refcount underflow with UAF diagnostics. Even if the most likely impact is DoS, the lifetime-corruption signal is strong enough that it should not be auto-closed without manual kernel/security review. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: nvmet-tcp: check INIT_FAILED before nvmet_req_uninit in digest error path Commit: 22ec7a9fe9153d2737ee9b2fa6d2e43a1491decf Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=22ec7a9fe9153d2737ee9b2fa6d2e43a1491decf Commit description: In nvmet_tcp_try_recv_ddgst(), when a data digest mismatch is detected, nvmet_req_uninit() is called unconditionally. However, if the command arrived via the nvmet_tcp_handle_req_failure() path, nvmet_req_init() had returned false and percpu_ref_tryget_live() was never executed. The unconditional percpu_ref_put() inside nvmet_req_uninit() then causes a refcount underflow, leading to a WARNING in percpu_ref_switch_to_atomic_rcu, a use-after-free diagnostic, and eventually a permanent workqueue deadlock. Check cmd->flags & NVMET_TCP_F_INIT_FAILED before calling nvmet_req_uninit(), matching the existing pattern in nvmet_tcp_execute_request(). Reviewed-by: Christoph Hellwig Signed-off-by: Shivam Kumar Signed-off-by: Keith Busch [shivam: inlined nvmet_tcp_finish_cmd() at the fix site for 5.10.y] Signed-off-by: Shivam Kumar Signed-off-by: Sasha Levin Changed files: drivers/nvme/target/tcp.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=22ec7a9fe9153d2737ee9b2fa6d2e43a1491decf ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64534 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64534 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:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 7.5 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).