From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74284][LOW] net/sched: sch_hfsc: Don't make class passive twice [ Upstream Date: Sat, 15 Aug 2026 19:30:38 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74284 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: a425c82ff06cda5165e0de3de8c2a445ec1f863e List-Id: CVE: CVE-2026-74284 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: net/sched: sch_hfsc: Don't make class passive twice [ Upstream Commit: a425c82ff06cda5165e0de3de8c2a445ec1f863e Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a425c82ff06cda5165e0de3de8c2a445ec1f863e Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74284 Analysis date: Sat, 15 Aug 2026 19:30:38 -0400 ActionableScore: 2 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate / Low-like Manual review required: NO Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74284 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74284 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-2026-74284 LOW 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:N/I:N/A:H';CWE-682;CWE-670;**CWE-400;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'HFSC qdisc active class accounting can become inconsistent when update_vf marks the same class passive twice during one dequeue path. A child qdisc such as codel or fq_codel can drop its last packets and notify HFSC before hfsc_dequeue later calls update_vf again for byte accounting. This can decrement a parent cl_nactive counter twice and remove a parent from the vttree even though sibling classes still have backlog, causing affected traffic to stop being dequeued. For the CVSS the PR:L reflects a conservative case where an untrusted local user can generate traffic through an already configured HFSC hierarchy, while creating or changing the qdisc normally requires CAP_NET_ADMIN. The issue is not directly network reachable as a standalone remote attack and depends on a specific traffic control configuration. Impact is denial of service for the affected qdisc or traffic classes, with no evidence of memory corruption, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) YES REMOTE NETWORK LINUS QDISC PACKET DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 1. ActionableScore * Conservative score: 1 * Paranoid score: 2 * Final recommended bucket: **Ordinary Moderate / Low-like** 2. Signal breakdown * Reliable qdisc-level DoS: +1. The bug can make an HFSC parent class inactive while sibling classes still have backlog, so affected traffic may stop being dequeued. * Availability impact realistic: +1 in the paranoid score. The stall can persist for the affected qdisc or traffic classes until configuration reset or recovery. * Local unprivileged trigger: +1 in the paranoid score only. If HFSC is already configured by an administrator, an unprivileged local user may be able to generate traffic that reaches the affected class hierarchy. * Requires CAP_NET_ADMIN in typical deployments: -2 in the conservative score. Creating or changing HFSC qdisc configuration normally requires administrative network privileges. * Rare or configuration-dependent subsystem: -1. HFSC is not the default qdisc in common deployments and the issue depends on a specific HFSC hierarchy with child qdiscs such as codel or fq_codel dropping their last packets during dequeue. * No memory corruption signal. The patch fixes state/accounting logic around cl_nactive and go_passive, not UAF, OOB write, double free, refcount misuse, or type confusion. * No privilege escalation signal. There is no demonstrated reclaim, overwrite, callback control, object confusion, or security-boundary bypass. 3. Reachability analysis The usual setup path requires CAP_NET_ADMIN because HFSC qdisc and class configuration is a traffic-control control-plane operation. After such a configuration exists, ordinary traffic may exercise the dequeue path, so a lower-privileged local user could be relevant in a paranoid deployment-specific interpretation. The issue is not directly network-reachable as a standalone remote attack because packets alone do not create the vulnerable HFSC configuration. Containers or delegated network namespaces could lower practical privileges if untrusted users are given CAP_NET_ADMIN or control over traffic shaping, but that is not the default host model. 4. Severity interpretation This behaves like an ordinary Moderate or Low-like DoS issue, not an Important-class kernel vulnerability. The realistic impact is traffic scheduling stall for the affected HFSC qdisc hierarchy. Theoretical impact does not extend to memory corruption or LPE based on the supplied patch and commit message. The main reason not to escalate is that the bug is a deterministic accounting/state bug, not a lifetime or overwrite primitive. 5. One-sentence report phrase HFSC qdisc class accounting can mark a class passive twice during dequeue, causing parent active counts to become inconsistent and affected traffic classes to stop dequeuing, with typical exploitation requiring CAP_NET_ADMIN setup or an already configured HFSC hierarchy. 6. Manual review recommendation NO MANUAL CHECK NEEDED. This is a configuration-dependent traffic-control DoS with no supported memory corruption, privilege escalation, confidentiality impact, or direct remote attack path. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net/sched: sch_hfsc: Don't make class passive twice [ Upstream Commit: a425c82ff06cda5165e0de3de8c2a445ec1f863e Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a425c82ff06cda5165e0de3de8c2a445ec1f863e Changed files: net/sched/sch_hfsc.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=a425c82ff06cda5165e0de3de8c2a445ec1f863e ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74284 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74284 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:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 4.7 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: 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).