From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98427][LOW] net/sched: codel: bound the dropping loop per dequeue call [ Upstream Date: Wed, 14 Oct 2026 22:13:59 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98427 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: 1 X-AL-KERNEL-Commit: bacd72289d34d8c05b7de5a12448b87b6dd93878 List-Id: CVE: CVE-2026-98427 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: net/sched: codel: bound the dropping loop per dequeue call [ Upstream Commit: bacd72289d34d8c05b7de5a12448b87b6dd93878 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bacd72289d34d8c05b7de5a12448b87b6dd93878 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98427 Analysis date: Wed, 14 Oct 2026 22:13:59 -0400 ActionableScore: 2 ActionableScore lower bound: 1 Actionable bucket: Ordinary Moderate Manual review required: NO Summary: A local unprivileged user can trigger a CPU soft lockup by filling a specially configured CoDel or FQ CoDel queue whose zero control-law increment causes one dequeue call to drain an unbounded backlog under the qdisc lock. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98427 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98427 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-2026-98427 LOW https://www.kernelcve.org/list/?q=CVE-2026-98427 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE AEGIS_AS=0 LEGACY=LOW RESULT=DIFF (independent Legacy and Aegis differ; FINAL: LOW, Aegis: 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-834;**CWE-400;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'The CoDel control law can truncate interval divided by sqrt count to zero when a very small interval is configured. This prevents drop_next from advancing and can keep the dropping loop running while it drains a large backlog under the qdisc lock. A local user can then generate traffic that causes prolonged CPU execution and a watchdog soft lockup. For the CVSS the PR:L value is used because an unprivileged local process can supply the triggering traffic after the vulnerable qdisc configuration already exists. The base AC:H reflects the required nondefault low interval configuration and suitable backlog, while the paranoid score uses AC:L for an environment where that configuration is already present and the queue can be filled reliably. The issue is not directly network reachable because packet traffic cannot by itself create the required qdisc configuration. Impact is denial of service through CPU soft lockup, with no supported memory corruption, confidentiality impact, integrity impact, or privilege escalation primitive. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 5.5 and the production ActionableScore returned 2 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE_KPANIC to MODERATE because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE to LOW because the ActionableScore threshold rule was applied. final reconciliation stage LOW to LOW because KP specialist did not establish a qualifying panic. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH and DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 and KPANIC_UNSUPPORTED_REMOVED. The independent weaker Aegis shadow evaluated CVSS 4.4 and ActionableScore 0 with primitive class CLASS_C and manual review RECOMMENDED. Its independently reconciled impact was MODERATE. The models disagreed but the aggregation rules retained the production result. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) MAYBE REMOTE DEADLOCK DANGER QDISC PACKET DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 KPANIC_UNSUPPORTED_REMOVED - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 ActionableScoreLower=1 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES RequiresHostUID0=NO AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO ## 1. ActionableScore * Raw conservative score: 1 * Conservative score: 1 * Raw paranoid score: 2 * Paranoid score: 2 * No floor or cap applied. * Final recommended bucket: **Ordinary Moderate**:: The conservative arithmetic is `+1 local unprivileged trigger +1 strong DoS -1 unusual attacker-independent configuration = 1`. The paranoid arithmetic is `+1 local unprivileged trigger +1 strong DoS = 2`. It omits the configuration penalty because an existing CoDel deployment may also accumulate excessive catch-up work after a long idle interval and large backlog. ## 2. Signal breakdown Positive signals: * `+1` Local unprivileged trigger. The commit explicitly states that an unprivileged user can generate traffic that triggers the soft lockup after the affected qdisc configuration exists. * `+1` Reliable strong DoS. The supplied reproducer causes a watchdog soft lockup while one `codel_dequeue()` invocation drains the backlog under the qdisc lock. Conservative negative signal: * `-1` Rare and difficult-to-reach configuration. The demonstrated reproducer requires a separately configured TBF and CoDel or FQ CoDel qdisc with an unusually small `2us` or `3us` interval. Creating that configuration normally requires a privileged control-plane operation that the triggering user does not perform. Not awarded: * No memory-corruption signal. The defect is an unbounded dropping loop caused by a zero control-law increment. * No UAF, OOB access, double release, refcount mutation, or stale-object use is established. * No remote-reachability points. Network traffic alone does not create the required qdisc configuration, and direct remote triggering is not demonstrated. * No extra Availability point. The watchdog soft lockup is already counted as the strong DoS consequence. * No confidentiality, integrity, authorization-bypass, or privilege-escalation signal. * NEW52 B5-R does not apply. There is no heap OOB write, retry-accumulated memory overwrite, or later consumption of corrupted structured state. * NEW53 B3-PENDING does not apply. No shared-backing write is present. * NEW54 B4-PENDING does not apply. No authorization decision or mandatory security guard is changed from DENY to ALLOW. * Common networking-core exposure is not awarded because this is a specifically configured qdisc control and dequeue path rather than a generally exercised default packet-processing path. ## 3. Reachability analysis The demonstrated attack has two roles. A privileged administrator first creates the TBF and CoDel or FQ CoDel configuration. After that setup, an ordinary local user can generate a UDP backlog and exercise the vulnerable dequeue path without UID 0 or an additional capability. The supplied evidence therefore establishes a below-host-admin triggering actor, so `HostAdminRequired=NO` and `RequiresHostUID0=NO`. It does not establish which user namespace governs every required qdisc setup operation or whether an ordinary user can create the complete configuration inside an attacker-created namespace. Therefore, `NamespaceScopedPrivilege=UNKNOWN`. Prior privileged setup is a material prerequisite for the demonstrated reproducer. The issue is not directly remotely reachable because arbitrary packets do not configure the qdisc, and no remote request-response path that reliably creates the required outgoing backlog is established. No race is involved. Once the zero control-law increment and sufficient backlog exist, the loop behavior is deterministic and repeatable. ## 4. Primitive and severity interpretation The exact defect is an arithmetic truncation and loop-bounding failure. For a sufficiently small interval, `interval/sqrt(count)` becomes zero, so `drop_next` does not advance. The dropping loop can consequently process the full backlog while holding the qdisc lock. This is a `CLASS_C` DoS primitive. It is not an active structured-object UAF, fixed stale storage case, lifetime violation, or authorization flaw. The demonstrated consequence is CPU soft lockup and degraded host availability. No useful primitive remains after excluding that DoS. The patch clamps the increment to at least one tick and limits a dequeue invocation to 256 drops before resynchronizing `drop_next`. `ImportantCandidate=NO` because there is no corruption, ownership violation, authorization bypass, or unresolved exploitation primitive. `AutoDowngradeAllowed=YES` because the established behavior is a configuration-dependent soft lockup with no evidence of confidentiality, integrity, or privilege-escalation impact. Operationally, this is an ordinary Moderate or Low-like denial-of-service issue. It is relevant where untrusted local workloads can generate traffic through an administrator-configured affected qdisc, but it does not require Important-class preservation. ## 5. One-sentence report phrase A local unprivileged user can trigger a CPU soft lockup by filling a specially configured CoDel or FQ CoDel queue whose zero control-law increment causes one dequeue call to drain an unbounded backlog under the qdisc lock. ## 6. Manual review recommendation NO MANUAL CHECK NEEDED The patch establishes a bounded DoS-only loop defect with no memory corruption, lifetime violation, authorization bypass, or unresolved security-boundary primitive. ## 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net/sched: codel: bound the dropping loop per dequeue call [ Upstream Commit: bacd72289d34d8c05b7de5a12448b87b6dd93878 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bacd72289d34d8c05b7de5a12448b87b6dd93878 Changed files: include/net/codel.h include/net/codel_impl.h 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=bacd72289d34d8c05b7de5a12448b87b6dd93878 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98427 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98427 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:L/UI:N/S:U/C:N/I:N/A:H 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: 1 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).