From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98104][MODERATE REGULAR] net/sched: cls_u32: fix duplicate handle when node ID pool is exhausted [ Upstream Date: Fri, 25 Sep 2026 15:13:58 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98104 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: 2 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 6890e28840bae4f6805e8de981c4ec8e12a4e064 List-Id: CVE: CVE-2026-98104 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: net/sched: cls_u32: fix duplicate handle when node ID pool is exhausted [ Upstream Commit: 6890e28840bae4f6805e8de981c4ec8e12a4e064 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6890e28840bae4f6805e8de981c4ec8e12a4e064 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98104 Analysis date: Fri, 25 Sep 2026 15:13:58 -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-2026-98104 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98104 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: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-98104 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98104 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:L/A:L';CWE-754;CWE-284;CWE-1284;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N';BEST CVSS score: '4.4';DESCR 'An exhausted cls_u32 node ID pool can cause gen_new_kid to return a handle that is already live instead of reporting an error. The duplicate handle can corrupt classifier bookkeeping because later cleanup may remove the ID reservation of a different live knode, and further filter additions can create additional aliases. A separate exhausted root table ID pool can publish root hash tables with handle 0, allowing cross-tcf_proto add lookup or delete operations within the same traffic control block. For the CVSS the PR:L value is used because a local user needs namespace local CAP_NET_ADMIN or equivalent delegated traffic control privileges to reliably create the required number of cls_u32 filters or protocol entries. The issue is not directly network reachable and is triggered through local traffic control configuration operations rather than packet traffic. Impact is primarily traffic classifier policy integrity degradation. In a conservative case repeated aliases can also disrupt classifier management and cause limited local denial of service. No memory corruption primitive or privilege escalation path is demonstrated by the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) YES REMOTE DANGER NOMEMCHK ERRORPATH NETWORK HARDWARE LINUS QDISC DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS 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**:: No floor or cap was applied. 2. Signal breakdown * +1 Local unprivileged trigger. The supplied reproduction states that an ordinary local user can create a user and network namespace with unshare -Urn, receive namespace-local CAP_NET_ADMIN, attach a clsact qdisc, and create the required cls_u32 objects. * +1 Weak indirect state corruption. Exhaustion of the node or root table handle pool causes duplicate cls_u32 handles and incorrect object selection. Later idr_remove operations can remove the reservation associated with a different live knode, causing further duplicate handles and inconsistent classifier bookkeeping. Not awarded: * No real UAF, double free, refcount mutation, stale post-lifetime access, OOB access, or arbitrary write is established. * No controlled reclaim, object replacement, callback influence, disclosure, or privilege escalation primitive is established. * No remote reachability is established. The trigger is rtnetlink traffic-control configuration, not packet processing. * No integrity point is awarded. Although cross-tcf_proto aliasing can alter classifier object lookup within a traffic-control block, the supplied evidence does not establish modification of policy owned by another security principal or a host-level policy bypass. * No availability point is awarded. The patch describes inconsistent handle management and incorrect add lookup delete behavior, but does not demonstrate a kernel crash, panic, persistent system-wide denial of service, or resource exhaustion. * No configuration rarity penalty is applied. CONFIG_NET_SCHED and CONFIG_CLS_U32 are required, but the attacker can create the relevant qdisc and filters at runtime once cls_u32 is available. * No privilege penalty is applied. The supplied context positively establishes completion of the full reproducer using attacker-created user and network namespaces. 3. Reachability analysis The evaluated attacker is an ordinary local user on a system that permits unprivileged user namespaces and has NET_SCHED and CLS_U32 available. The supplied reproduction explicitly states that the attacker can use unshare -Urn, obtain CAP_NET_ADMIN in the new network namespace, attach clsact to a namespace-local device, and create 4095 or 2047 cls_u32 objects to exhaust the relevant handle pool. The relevant rtnetlink and qdisc management capability checks are namespace-scoped for objects created in the attacker network namespace. The supplied conditions describe the complete trigger sequence as namespace-local, including qdisc creation and filter or protocol creation. Therefore HostAdminRequired is NO and NamespaceScopedPrivilege is YES for the stated reproducer. No prior host-admin setup, special hardware, race condition, firmware interaction, or external network access is required beyond kernel support for the traffic-control components. The attack is deterministic but requires thousands of local configuration operations. 4. Primitive and severity interpretation The exact primitive is duplicate identifier generation and handle aliasing in cls_u32 after a finite ID pool is exhausted. gen_new_kid can return an already live knode handle, while gen_new_htid can produce root hash-table handle zero. This permits incorrect lookup or deletion behavior and can compound classifier bookkeeping inconsistency when an error path removes the IDR reservation of a different live knode. This is an invalid-state and object-selection bug, not a memory-lifetime bug. There is no evidence that a knode or hash table is freed while a stale reference is used. There is no concrete repeated release, put, free, or refcount operation on a dangling object. The issue is therefore CLASS_C rather than CLASS_A or CLASS_B. The practical demonstrated consequence is namespace-local traffic-classifier configuration inconsistency. Cross-tcf_proto aliasing is limited by the supplied evidence to objects in the same traffic-control block. A stronger consequence such as host policy bypass, cross-namespace interference, kernel memory corruption, information disclosure, or privilege escalation is speculative and is not scored. ImportantCandidate is NO because the patch establishes no meaningful unresolved corruption or security-boundary primitive beyond local classifier state inconsistency. AutoDowngradeAllowed is YES because the issue has no demonstrated UAF, arbitrary write, protected-object access, authorization bypass, or unresolved lifetime corruption mechanism. Likely operational severity is ordinary Moderate or Low-like local impact. Systems that permit unprivileged user namespaces may allow a local user to corrupt only their own namespace-local cls_u32 classifier configuration. Host traffic-control policy is not shown to be affected. 5. One-sentence report phrase A local user with namespace-local CAP_NET_ADMIN can exhaust cls_u32 handle pools and cause duplicate filter or root table handles, resulting in inconsistent local traffic classifier bookkeeping without demonstrated kernel memory corruption or privilege escalation. 6. Manual review recommendation NO MANUAL CHECK NEEDED The supplied patch establishes a deterministic local handle-exhaustion logic bug, but it does not establish memory corruption, a lifetime violation, host-level policy modification, cross-namespace impact, or a privilege-escalation path. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net/sched: cls_u32: fix duplicate handle when node ID pool is exhausted [ Upstream Commit: 6890e28840bae4f6805e8de981c4ec8e12a4e064 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6890e28840bae4f6805e8de981c4ec8e12a4e064 Changed files: net/sched/cls_u32.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=6890e28840bae4f6805e8de981c4ec8e12a4e064 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98104 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98104 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:L/A:N The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L The Best / paranoid CVSS score: 4.4 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: 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: 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).