From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-90072][LOW] net/sched: sfq: clamp quantum to avoid signed overflow soft lockup [ Upstream Date: Thu, 17 Sep 2026 13:43:15 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-90072 X-AL-KERNEL-Priority: LOW X-AL-KERNEL-Severity: LOW X-AL-KERNEL-Base-Severity: LOW X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 1 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 86799499585af06a9431c9e7782658667bd62650 List-Id: CVE: CVE-2026-90072 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: net/sched: sfq: clamp quantum to avoid signed overflow soft lockup [ Upstream Commit: 86799499585af06a9431c9e7782658667bd62650 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=86799499585af06a9431c9e7782658667bd62650 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90072 Analysis date: Thu, 17 Sep 2026 13:43:15 -0400 ActionableScore: 1 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-2026-90072 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90072 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: LOW 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-2026-90072 LOW https://www.kernelcve.org/list/?q=CVE-2026-90072 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-190;*CWE-835;**CWE-400;BEST CVSS score: '5.5';DESCR 'An unchecked MTU derived quantum in SFQ can enter the signed range or become zero, causing the refill logic in sfq_dequeue to loop indefinitely while the qdisc lock is held. A local user can trigger the condition by creating or controlling a suitable network device, assigning an extreme MTU, and initializing SFQ. For the CVSS the PR:L is selected because CAP_NET_ADMIN in a user namespace is sufficient and does not require full host administrative control. The issue is not directly network reachable because packet traffic alone cannot create the required device and qdisc configuration. Impact is denial of service through excessive CPU consumption, a soft lockup, and disruption of network scheduling. There is no UAF, OOB access, information leak, or write primitive that would support confidentiality, integrity, or privilege escalation impact.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) SKIP CVE-2026-90072 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE REMOTE DEADLOCK DANGER SIMPLEFIX NETWORK HARDWARE QDISC DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=1 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=YES ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 1 * Conservative score: 1 * Raw paranoid score: 1 * Paranoid score: 1 * No floor or cap was applied. * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * +1 Reliable strong DoS. The invalid quantum makes `sfq_dequeue()` loop indefinitely while holding the qdisc lock, producing a CPU soft lockup and disrupting network scheduling. * +0 Local unprivileged trigger. The complete operation is namespace-scoped, but availability of unprivileged user-namespace creation is not established for every affected deployment. * +0 Privilege penalty. Host-admin privilege is not required, while the supplied evidence directly identifies `CAP_NET_ADMIN` in a user namespace as sufficient. No separate delegated-service prerequisite is established. * +0 Integer overflow. The signed reinterpretation is concrete, but it produces an infinite loop rather than memory corruption. * +0 Additional availability. The soft lockup and scheduling disruption are the same DoS consequence and are not counted twice. * +0 Common networking path. SFQ initialization is locally configured control-plane functionality, not a directly reachable common packet-processing vulnerability. * No UAF, OOB access, overwrite, disclosure, controlled reclaim, authorization bypass, or privilege-escalation primitive is established. * Remote reachability is not awarded because network packets cannot create the required device, extreme MTU, and SFQ configuration. * The paranoid score is not increased because the established mechanics remain deterministic DoS only. No stronger primitive is technically supported. 3. Reachability analysis A user with `CAP_NET_ADMIN` in the relevant user and network namespace can create or control a suitable dummy device, assign the extreme MTU, and initialize SFQ. The supplied commit explicitly states that a user-namespace capability is sufficient, so host-admin-equivalent privilege is not required and the complete privilege-gated sequence is treated as namespace-scoped. Whether an ordinary user can obtain that capability depends on the deployment allowing attacker-created user and network namespaces. This uncertainty prevents awarding the ordinary local-unprivileged bonus, but it does not justify a host-admin penalty. No special hardware, boot option, firmware behavior, prior host-created topology, or timing race is required. The trigger is deterministic once the configuration is available. 4. Primitive and severity interpretation The exact primitive is an unchecked MTU-derived unsigned quantum that reaches the signed range, or becomes zero, and prevents the SFQ refill loop from making progress. This is a logic and integer-arithmetic defect with an infinite-loop consequence. There is no stale storage, active structured-object UAF, repeated release, refcount mutation, or memory-corruption primitive. The issue is therefore `CLASS_C`, with soft lockup and network scheduling disruption as the demonstrated consequences. Confidentiality, integrity, privilege escalation, and useful exploitation leverage beyond DoS are unsupported. `ImportantCandidate=NO` because the patch establishes only a namespace-capability-gated local DoS. `AutoDowngradeAllowed=YES` because no unresolved corruption, ownership, lifetime, or security-boundary primitive would be lost by ordinary automated handling. 5. One-sentence report phrase An attacker with CAP_NET_ADMIN in a user namespace can configure an extreme device MTU that gives SFQ an invalid quantum, causing sfq_dequeue to loop under the qdisc lock and trigger a local CPU soft lockup and denial of service. 6. Manual review recommendation NO MANUAL CHECK NEEDED The defect is a well-bounded deterministic DoS with no memory corruption, disclosure, authorization bypass, or privilege-escalation primitive. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net/sched: sfq: clamp quantum to avoid signed overflow soft lockup [ Upstream Commit: 86799499585af06a9431c9e7782658667bd62650 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=86799499585af06a9431c9e7782658667bd62650 Changed files: net/sched/sch_sfq.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=86799499585af06a9431c9e7782658667bd62650 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-90072 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90072 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: Not available The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 5.5 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: unknown Paranoid ActionableScore: 1 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: LOW KPANIC detected for this report: NO Published priority for this report (same as in Subject): LOW 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).