From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-89968][MODERATE 7.0] nvmet-tcp: reject unsolicited H2CData PDUs Date: Wed, 16 Sep 2026 14:58:26 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-89968 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: 4 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 02341ee424fb2eed16b5b8a9d247492e49335c21 List-Id: CVE: CVE-2026-89968 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: nvmet-tcp: reject unsolicited H2CData PDUs Commit: 02341ee424fb2eed16b5b8a9d247492e49335c21 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=02341ee424fb2eed16b5b8a9d247492e49335c21 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89968 Analysis date: Wed, 16 Sep 2026 14:58:26 -0400 ActionableScore: 4 ActionableScore lower bound: unknown Actionable bucket: Borderline / manual review recommended Manual review required: YES Summary: An unauthenticated remote NVMe/TCP host can send unsolicited H2CData before R2T, causing double command completion and corrupting response list state, which can crash the kernel or wedge the nvmet_tcp workqueue. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-89968 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89968 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-2026-89968 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89968 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';*CWE-20;CWE-841;*CWE-835;*CWE-672;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.6';DESCR 'An unsolicited H2CData PDU in the NVMe/TCP target path can be accepted before the target has sent an R2T for the command. A remote host can submit a write command that takes the R2T path and then send H2CData for the same tag before R2T is transmitted, causing early command completion and a later second completion on an error path. This can add the same command to the response list twice and create a self referential list node, resulting in a kernel BUG with CONFIG_DEBUG_LIST or a wedged nvmet_tcp workqueue and soft lockup without it. For the CVSS the PR:N is used for the paranoid score because an allow_any_host subsystem can be reached without authentication once the attacker has access to the NVMe/TCP target network. The issue is network reachable inside the storage fabric, but NVMe/TCP targets are usually deployed on isolated storage or data center networks rather than the public Internet. Impact is at least denial of service via kernel crash or workqueue lockup and in worst case may allow limited confidentiality or integrity impact due to kernel list state corruption and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4) YES REMOTE DEADLOCK DANGER NVME NETWORK LINUS KPANIC KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES ## 1. ActionableScore * Raw conservative score: 4 * Conservative score: 4. No floor or cap applied. * Raw paranoid score: 4 * Paranoid score: 4. No additional paranoid point awarded because no useful primitive beyond crash or workqueue wedge is established. * Final recommended bucket: **Borderline / manual review recommended**:: ## 2. Signal breakdown Positive signals: * +2 Remote reachable / directly network-triggerable: a remote NVMe/TCP host can send an unsolicited H2CData PDU before R2T is sent. * +1 Reliable kernel crash / strong DoS: CONFIG_DEBUG_LIST can trigger a kernel BUG, and without it the nvmet_tcp workqueue can wedge in a soft lockup. * +1 Weak / indirect corruption candidate: the same command can be added twice to response list state, creating a self-referential llist node. This is kernel list state corruption, but the demonstrated consequence is DoS. Negative signals: * No negative privilege penalty: host-admin-equivalent privilege is not required for the remote host when an allow_any_host subsystem is reachable. * No rare-subsystem penalty: NVMe/TCP targets are often isolated storage-fabric services, but isolation is deployment-dependent and not a concrete scoring penalty. Important non-awarded signals: * RealUAF not awarded: no object free followed by stale use is established. * Controlled reclaim not demonstrated. * Arbitrary write not demonstrated. * Confidentiality and integrity not awarded: list state corruption is shown, but no disclosure, protected-object modification, or attacker-directed write primitive is established. * Strong LPE / strong exploitation leverage not awarded: no controlled object replacement, callback control, refcount takeover, or privilege escalation path is shown. * Extra Availability point not awarded: the BUG and workqueue wedge are the same availability consequence already counted as strong DoS. * Concrete repeated release/refcount not awarded: the bug is double completion and double list insertion, not a second put/release/refcount mutation on a potentially freed object. * FLOOR 5 not applied: no UAF, no repeated lifetime mutation, and no meaningful exploitation surface beyond crash/list wedge is established. ## 3. Reachability analysis The evaluated attacker is a remote NVMe/TCP host that can connect to the target subsystem. The supplied text explicitly states that the issue is remotely triggerable and needs no authentication on an allow_any_host subsystem. HostAdminRequired=NO because the complete trigger does not require host administrative privileges on the victim once the NVMe/TCP target is exposed to the attacker. NamespaceScopedPrivilege=NO because the trigger is network protocol access, not a namespace-scoped local capability path. There is a prior deployment prerequisite: the victim must run an NVMe/TCP target and expose a subsystem reachable by the attacker. In practice this is commonly an isolated storage or data-center network rather than the public Internet, but that does not remove remote reachability for triage. No timing race is required. The attack is an ordered protocol-state violation: submit a write command that takes the R2T path, send H2CData before R2T, and reach double completion on the error path. ## 4. Primitive and severity interpretation The exact primitive is unsolicited H2CData acceptance before the target has sent R2T. This can cause early command completion and later second completion, resulting in the same command being queued twice on response list state. This is not a real UAF and not a repeated release/refcount bug. It is active kernel protocol/list state corruption, but the demonstrated outcome is kernel BUG or workqueue soft lockup. After excluding the crash/wedge, no independently useful attacker-controlled corruption primitive is established. PrimitiveClass=CLASS_C because the behavior is primarily remote DoS through invalid protocol state and list corruption without demonstrated confidentiality, integrity, UAF, arbitrary write, controlled reclaim, or privilege-escalation leverage. ImportantCandidate=NO because the evidence does not show Important-grade exploitation leverage beyond DoS. ManualReview=RECOMMENDED because the issue is remotely reachable and unauthenticated in allow_any_host configurations. AutoDowngradeAllowed=YES because the established primitive remains crash/DoS-only and no unresolved Class A or strong Class B primitive is present. Likely operational severity: actionable as a remote storage-fabric DoS, but not an Important-class kernel corruption candidate based on supplied evidence. ## 5. One-sentence report phrase An unauthenticated remote NVMe/TCP host can send unsolicited H2CData before R2T, causing double command completion and corrupting response list state, which can crash the kernel or wedge the nvmet_tcp workqueue. ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED Reason: the issue is remotely reachable and unauthenticated in allow_any_host NVMe/TCP deployments, but the demonstrated primitive is DoS-only list-state corruption without UAF, controlled reclaim, arbitrary write, or privilege-escalation evidence. ## 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: nvmet-tcp: reject unsolicited H2CData PDUs Commit: 02341ee424fb2eed16b5b8a9d247492e49335c21 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=02341ee424fb2eed16b5b8a9d247492e49335c21 Commit description: nvmet_tcp_handle_h2c_data_pdu() accepts an H2CData PDU after only checking that its TTAG is a valid in-range command index and that the command's data buffers are mapped. It never checks that the target has actually solicited that data by sending an R2T for the command. A remote host can abuse this. It submits a write command that takes the R2T path and, before the target transmits the R2T, sends an H2CData PDU for that command's tag. The data completes the command early, and when the command then fails synchronously (e.g. a length mismatch caught by nvmet_check_transfer_len()), it is completed a second time. Each completion calls nvmet_tcp_queue_response(), so the same command is added to queue->resp_list twice while it is still linked; the second llist_add() makes the node point to itself (lentry->next == lentry). nvmet_tcp_process_resp_list() then walks that self-referential node and adds the command to resp_send_list twice. With CONFIG_DEBUG_LIST this trips the "list_add double add" check (kernel BUG); without it the loop never terminates and the nvmet_tcp workqueue wedges (soft-lockup). It is remotely triggerable and needs no authentication on an allow_any_host subsystem. Track whether an R2T has been transmitted for a command and reject an H2CData PDU that arrives before it. The flag is cleared on command reuse (nvmet_tcp_get_cmd() zeroes cmd->flags) and stays set across the multiple H2CData PDUs of a single solicited transfer. Fixes: 872d26a ("nvmet-tcp: add NVMe over TCP target driver") Cc: stable@vger.kernel.org Reviewed-by: Sagi Grimberg Signed-off-by: Shivam Kumar Signed-off-by: Keith Busch Signed-off-by: Greg Kroah-Hartman 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=02341ee424fb2eed16b5b8a9d247492e49335c21 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-89968 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89968 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:L/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS score: 7.6 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: unknown Paranoid ActionableScore: 4 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).