From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-90364][MODERATE REGULAR] ACPI: processor: Unregister cpufreq notifier on init failure [ Upstream Date: Thu, 17 Sep 2026 18:50:11 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-90364 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: 3 X-AL-KERNEL-ActionableScore-Lower: 2 X-AL-KERNEL-Commit: ccee0785030978c49505e04954eee3f30a5f01ca List-Id: CVE: CVE-2026-90364 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: ACPI: processor: Unregister cpufreq notifier on init failure [ Upstream Commit: ccee0785030978c49505e04954eee3f30a5f01ca Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ccee0785030978c49505e04954eee3f30a5f01ca Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90364 Analysis date: Thu, 17 Sep 2026 18:50:11 -0400 ActionableScore: 3 ActionableScore lower bound: 2 Actionable bucket: Borderline / manual review recommended Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-90364 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90364 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: YES A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-90364 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-90364 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:H/UI:N/S:U/C:H/I:H/A:H';CWE-459;*CWE-772;*CWE-416;CWE-703;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.4';DESCR 'The ACPI processor init path can leave the cpufreq policy notifier registered when driver_register or cpuhp_setup_state fails after notifier registration. A later cpufreq policy notification may then hit a stale or inconsistent callback state, causing a kernel crash and denial of service. In module builds, a failed init can be more sensitive because the module may be unloaded while the notifier list still holds a reference to module data or callback code, making this a plausible stale notifier UAF candidate. For the CVSS the PR:H is used because reliable triggering normally requires administrative control over module loading or kernel initialization failure conditions. The issue is local and not network reachable. Impact is at least denial of service, with a paranoid manual review case for confidentiality and integrity because stale notifier callbacks can represent memory corruption risk.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3) YES DANGER INIT SIMPLEFIX ERRORPATH HARDWARE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=3 ActionableScoreLower=2 PrimitiveClass=CLASS_B RealUAF=YES HostAdminRequired=YES NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 2 * Conservative score: 2. No floor or cap applied. Real UAF floor is not applied because host-admin-equivalent reachability is positively established. * Raw paranoid score: 3 * Paranoid score: 3. No floor or cap applied. * Final recommended bucket: **Borderline / manual review recommended**:: 2. Signal breakdown Conservative signals: * +2 Real UAF / lifetime violation. If the ACPI processor code is built as a module and init fails after cpufreq notifier registration, the failed module init path can leave a notifier registered after the module is torn down. * +1 Reliable kernel crash / strong DoS. A later cpufreq policy notification may call a stale notifier callback or use inconsistent ACPI processor state. * +1 Concrete persistent kernel reference / registration leak. The cpufreq notifier remains registered even though the initialization path failed and normal cleanup should have removed it. * -2 Host-admin-equivalent privilege required. Reliable triggering requires module loading or kernel initialization failure control, which is host-admin-level in the supplied evidence. Paranoid additional signal: * +1 Active stale callback concern. The stale object is a notifier registration that may later be consumed by the cpufreq notifier chain as an active callback path, not merely passive leaked metadata. Important non-awarded signals: * Controlled reclaim not demonstrated. * Arbitrary write not demonstrated. * Privilege escalation not demonstrated. * Remote reachability not established. * Namespace-scoped reachability not established. * Concrete repeated release/refcount operation not established. * Structured stale-object leverage beyond the stale callback concern is not awarded because attacker-controlled replacement or callback influence is not shown. * Extra Availability is not awarded because the same crash is already counted. * C/I impact is not awarded in conservative scoring because no disclosure, arbitrary write, or attacker-controlled post-free reuse is established. Repeated-release/refcount check: * First release can end lifetime: module init failure can unload/free module-owned code/data in module builds. * Exact same reference survives: the notifier registration may remain in the cpufreq notifier list. * Second operation mutates lifetime/refcount: no concrete second put/release/refcount mutation is shown. * +1 Concrete repeated release/refcount: not awarded. * Paranoid repeated-refcount leverage: not awarded. * FLOOR 5: not applied. 3. Reachability analysis The plausible trigger is local and privileged. The vulnerable sequence requires `acpi_processor_driver_init()` to register the cpufreq policy notifier and then fail later in `driver_register()` or `cpuhp_setup_state()`. In a module build, a failed init can cause module teardown while the notifier remains registered. Ordinary local user reachability is not established. Namespace-scoped capability reachability is not relevant here. No network path is involved. The complete trigger appears to require host administrator control over module loading or equivalent kernel initialization conditions. There is no attacker-created namespace object, no sysctl-user data-plane trigger, and no packet-processing path. The path is an init failure/error-cleanup path. No race is required by the patch context. 4. Primitive and severity interpretation The exact primitive is a stale cpufreq notifier registration left behind after ACPI processor initialization fails. In module builds, this can plausibly become a stale pointer to module-owned notifier data or callback code after the failed module is unloaded. This is an active structured object because a notifier block participates in later callback dispatch. It is not a fixed DMA or IO buffer. However, the supplied evidence does not show controlled reclaim, attacker-controlled replacement contents, arbitrary read/write, or a practical LPE chain. PrimitiveClass is CLASS_B because a real lifetime/stale callback primitive is plausible and technically meaningful, but exploitation leverage beyond crash is unresolved and strongly privilege-gated. Demonstrated consequence is denial of service through crash or invalid callback/state use. Speculative consequence is broader memory corruption if module memory reuse interacts badly with the stale notifier, but this is not established enough for CLASS_A. ImportantCandidate is NO because the complete trigger is host-admin-equivalent and no below-host-admin boundary bypass, controlled corruption, or privilege escalation path is established. AutoDowngradeAllowed is YES because this is a constrained privileged init-failure lifetime bug with no demonstrated meaningful reuse primitive beyond crash. Likely operational severity is ordinary to borderline Moderate, with manual review useful mainly to confirm module-vs-built-in behavior and whether downstream products allow unusual non-admin module/init control. 5. One-sentence report phrase The ACPI processor init failure path may leave a cpufreq policy notifier registered after initialization fails, which can create a stale notifier callback risk in module builds and cause a local host-admin-triggered kernel crash. 6. Manual review recommendation MANUAL CHECK RECOMMENDED Reason: the issue is not a strong Important candidate from supplied evidence, but stale notifier callbacks after failed module init are lifetime-sensitive and should be checked against actual build configuration and module unload behavior. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: ACPI: processor: Unregister cpufreq notifier on init failure [ Upstream Commit: ccee0785030978c49505e04954eee3f30a5f01ca Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ccee0785030978c49505e04954eee3f30a5f01ca Changed files: drivers/acpi/processor_driver.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=ccee0785030978c49505e04954eee3f30a5f01ca ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-90364 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90364 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:H/PR:H/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 6.4 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: 2 Paranoid ActionableScore: 3 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).