From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-90324][MODERATE REGULAR] ublk: check import_ubuf() return value [ Upstream Date: Fri, 18 Sep 2026 04:31:53 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-90324 X-AL-KERNEL-Priority: MODERATE REGULAR X-AL-KERNEL-Severity: MODERATE REGULAR X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 2 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 0121c84adb6a4cd6f7560b5895bd88f9899bbc1f List-Id: CVE: CVE-2026-90324 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: ublk: check import_ubuf() return value [ Upstream Commit: 0121c84adb6a4cd6f7560b5895bd88f9899bbc1f Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0121c84adb6a4cd6f7560b5895bd88f9899bbc1f Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90324 Analysis date: Fri, 18 Sep 2026 04:31:53 -0400 ActionableScore: 2 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate Manual review required: NO Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-90324 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90324 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 REGULAR Manual review required: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-90324 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-90324 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-457;CWE-252;CWE-908;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'An unchecked import_ubuf failure can leave a stack allocated iov_iter uninitialized before it is passed to ublk_copy_user_pages. A local ublk userspace server can trigger the failure by supplying a buffer range outside the permitted user address space. The immediate and reliably supported impact is denial of service through an invalid memory access or kernel crash. The uninitialized iterator also contains operation type, length, offset, and buffer representation fields, so subsequent copy processing may select an invalid iterator path and create a potential memory corruption condition. For the CVSS the PR:L value is used because triggering requires a local process with access to the ublk server interface, but does not necessarily require unrestricted host administration in every deployment. The issue is not network reachable. For the paranoid score, CIA:HHH with AC:H represents the highest still defensible interpretation because exploitation beyond a crash would require difficult control over uninitialized stack state and the resulting iterator behavior.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) SKIP CVE-2026-90324 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE OOB SIMPLEFIX DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 2 * Conservative score: 2 * Raw paranoid score: 2 * Paranoid score: 2 * No floor or cap applied. * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * +1 Weak or indirect corruption candidate. A failed `import_ubuf()` leaves `iov_iter` uninitialized, and the structure is then consumed by `ublk_copy_user_pages()`. * +1 Realistic kernel crash or strong DoS. Invalid iterator type, pointer, length, or offset fields can cause an invalid memory access in the copy path. * +0 Strong corruption primitive. Attacker control over the uninitialized stack contents, copy destination, or resulting kernel access is not established. * +0 Strong semantic reinterpretation. The iterator is consumed as a structured descriptor, but the required validation-under-one-semantics and consumption-under-another-semantics chain is not established. * +0 Local unprivileged trigger. A userspace ublk server controls the rejected address, but ordinary unprivileged access to the complete ublk setup and data path is not established. * +0 Confidentiality and integrity. No disclosure, directed write, controlled target, or protected-state modification is demonstrated. * +0 Additional Availability. The possible crash is already counted once. * +0 Remote reachability. The vulnerable interface is local. * No negative privilege penalty was applied because host-admin-equivalent privilege is not positively established. * No race or timing penalty applies. Supplying an invalid address is an ordered input-validation failure, not a race. * Controlled reclaim, arbitrary kernel read or write, callback influence, UAF, and privilege escalation are not demonstrated. 3. Reachability analysis The triggering actor is a local userspace ublk server that supplies `io->buf.addr` and a length outside the permitted userspace address range. The failure itself is deterministic once that invalid range is processed. The supplied evidence does not establish whether the complete device creation, server registration, and affected request path are available to an ordinary user, a delegated storage service, or only a host administrator. Therefore, `HostAdminRequired` and `NamespaceScopedPrivilege` remain `UNKNOWN`, and neither a privilege penalty nor an unprivileged-trigger bonus is applied. A configured ublk device and active userspace server are prerequisites. No special hardware, network access, namespace behavior, boot option, or timing race is established. 4. Primitive and severity interpretation The exact primitive is use of an uninitialized stack `iov_iter` after an unchecked `import_ubuf()` failure. The iterator is an active copy descriptor containing type, direction, offset, count, and backing representation state. Passing it to `ublk_copy_user_pages()` can therefore select invalid copy behavior. This is not a UAF, repeated release, lifetime violation, or fixed stale-storage case. The patch supports invalid structured-state consumption and a plausible kernel fault, but it does not establish attacker control over the uninitialized fields or an independently useful memory-corruption primitive. The demonstrated practical consequence is local DoS or request-path failure. Kernel memory corruption and privilege escalation remain theoretical because no controllable destination, payload, replacement object, disclosure path, or arbitrary access is shown. The issue is therefore `CLASS_C`, not `CLASS_A` or `CLASS_B`. `ImportantCandidate=NO` because meaningful exploitation leverage beyond a fault is not established. `AutoDowngradeAllowed=YES` because no unresolved lifetime, ownership, authorization, or controlled-corruption primitive remains. Manual review is still recommended to inspect the implementation of `ublk_copy_user_pages()` and the reachable `iov_iter` dispatch paths. 5. One-sentence report phrase An unchecked `import_ubuf()` failure can pass an uninitialized `iov_iter` into the ublk page-copy path, allowing a local ublk server to cause invalid memory access and potentially crash the kernel. 6. Manual review recommendation MANUAL CHECK RECOMMENDED Review whether any reachable `iov_iter` type can turn attacker-influenced stack residue into a kernel-memory read or write before faulting. Without such evidence, this remains a local crash or DoS issue. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: ublk: check import_ubuf() return value [ Upstream Commit: 0121c84adb6a4cd6f7560b5895bd88f9899bbc1f Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0121c84adb6a4cd6f7560b5895bd88f9899bbc1f Changed files: drivers/block/ublk_drv.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=0121c84adb6a4cd6f7560b5895bd88f9899bbc1f ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-90324 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90324 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:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 7 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: 2 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: NO Published priority for this report (same as in Subject): MODERATE REGULAR 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).