From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98009][LOW] net/sched: ets: clamp quantum in parse and fallback paths [ Upstream Date: Fri, 25 Sep 2026 09:11:52 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98009 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: 2 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 99ae477b892e203a37985ebc56f0063e072f7f4b List-Id: CVE: CVE-2026-98009 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: net/sched: ets: clamp quantum in parse and fallback paths [ Upstream Commit: 99ae477b892e203a37985ebc56f0063e072f7f4b Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=99ae477b892e203a37985ebc56f0063e072f7f4b Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98009 Analysis date: Fri, 25 Sep 2026 09:11:52 -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-2026-98009 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98009 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-2026-98009 LOW https://www.kernelcve.org/list/?q=CVE-2026-98009 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-835;**CWE-400;*CWE-20;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'An ETS qdisc can enter an unbounded deficit refill loop while holding the qdisc lock when a zero or excessively small quantum is combined with a crafted packet size table and a headerless device whose psched_mtu is zero. A local actor can create such a qdisc on a dummy device and cause a CPU soft lockup, leaving the affected qdisc locked and consuming CPU time. For the CVSS the PR:L is selected because reliable triggering requires local control of network namespace configuration and CAP_NET_ADMIN. On systems that permit unprivileged user namespaces this capability can be obtained in an attacker controlled user and network namespace. The issue is not directly network reachable. Impact is denial of service. It is most directly confined to the affected namespace and CPU, but can reduce host availability on constrained systems.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) YES REMOTE DANGER INIT SIMPLEFIX NETWORK HARDWARE QDISC DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=YES ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 2 * Conservative score: 2 * Raw paranoid score: 2 * Paranoid score: 2 * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * +1 Local unprivileged trigger. The supplied reproduction states that `unshare -Urn` is sufficient, allowing an ordinary user on systems permitting unprivileged user namespaces to obtain CAP_NET_ADMIN in an attacker controlled user and network namespace. * +1 Reliable denial of service. A crafted ETS qdisc configuration can make the deficit refill loop spin while holding the qdisc lock, causing CPU soft lockup and preventing normal progress for that qdisc. No additional points: * No UAF, stale object access, OOB access, refcount corruption, ownership violation, or authorization bypass is established. * No controlled reclaim, arbitrary write, callback control, disclosure, integrity impact, or privilege escalation primitive is demonstrated. * No remote reachability is established. The vulnerable path is reached through local qdisc configuration, not packet traffic. * No local unprivileged high-control kernel data plane API point is awarded. The attacker configures a qdisc, but does not obtain control over a memory layout, object lifetime, allocator state, or kernel payload relevant to exploitation. * No second Availability point is awarded. The CPU soft lockup and qdisc lock stall are the same DoS consequence. * No paranoid-only point is awarded. The higher CVSS Availability interpretation reflects possible operational impact on constrained systems, but does not establish an additional exploitation primitive for ActionableScore purposes. 3. Reachability analysis The attacker is a local ordinary user on systems where unprivileged user namespaces are enabled. The supplied reproduction explicitly states that `unshare -Urn` suffices. The relevant qdisc and rtnetlink operations are namespace scoped. The attacker can create an attacker controlled user namespace and network namespace, receive CAP_NET_ADMIN in that namespace, create or use a dummy network device there, attach the ETS qdisc, and configure the low quantum values that trigger the loop. Therefore the complete demonstrated trigger is namespace scoped and does not require host administrator privilege. The affected kernel must be built with `CONFIG_NET_SCH_ETS=y` or otherwise provide the ETS qdisc. This is an affected-kernel feature requirement, not evidence that a separate host administrator must prepare the attack path at runtime. No special hardware, firmware, race, privileged host device, or prior host-created topology is required by the supplied reproduction. 4. Primitive and severity interpretation The exact primitive is an invalid scheduler configuration leading to an unbounded deficit refill loop. A zero or too-small quantum can combine with a very large packet length and a zero `psched_mtu()` fallback value, causing ETS dequeue processing to spin while holding the qdisc lock. This is not a memory corruption issue. There is no active structured stale object, no use-after-free, no repeated release or refcount mutation, no arbitrary or directed write, and no attacker controlled post-free state. The demonstrated consequence is CPU consumption, qdisc lock retention, and a CPU soft lockup. The issue is therefore `CLASS_C`, representing an invalid-state DoS condition. The impact can be meaningful in a constrained environment, especially on systems with few CPUs or where the affected qdisc is important for local network processing. However, the demonstrated impact remains denial of service. There is no patch-supported basis for confidentiality, integrity, privilege escalation, host escape, or Important-class exploitation leverage. ImportantCandidate is NO because the patch establishes only a local scheduler-loop DoS primitive. AutoDowngradeAllowed is YES because no unresolved kernel corruption, lifetime, ownership, authorization, or boundary-bypass primitive would be discarded by an ordinary Moderate classification. 5. One-sentence report phrase A local user can configure an ETS qdisc with an invalidly small quantum in an attacker controlled network namespace, causing an unbounded deficit refill loop under the qdisc lock and resulting in CPU soft lockup and denial of service. 6. Manual review recommendation NO MANUAL CHECK NEEDED The issue is a namespace-reachable local DoS caused by an infinite scheduler loop, with no demonstrated memory corruption, privilege escalation, security-boundary bypass, confidentiality impact, or integrity impact. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net/sched: ets: clamp quantum in parse and fallback paths [ Upstream Commit: 99ae477b892e203a37985ebc56f0063e072f7f4b Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=99ae477b892e203a37985ebc56f0063e072f7f4b Changed files: net/sched/sch_ets.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=99ae477b892e203a37985ebc56f0063e072f7f4b ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98009 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98009 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:L 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: 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: 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).