From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-90109][LOW] net: sched: fix 32-bit backlog wrap in gred, bfifo and plug enqueue [ Upstream Date: Thu, 17 Sep 2026 13:21:34 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-90109 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: 3fb51b3960342bbee563543f8d33710fd0fb5a96 List-Id: CVE: CVE-2026-90109 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: net: sched: fix 32-bit backlog wrap in gred, bfifo and plug enqueue [ Upstream Commit: 3fb51b3960342bbee563543f8d33710fd0fb5a96 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3fb51b3960342bbee563543f8d33710fd0fb5a96 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90109 Analysis date: Thu, 17 Sep 2026 13:21:34 -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-2026-90109 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90109 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-2026-90109 LOW https://www.kernelcve.org/list/?q=CVE-2026-90109 CHECK WITH IMPACT FROM ORIG NN IMPORTANT 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-190;**CWE-400;CWE-770;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'A 32-bit integer wrap in the net scheduler enqueue paths for gred, bfifo, and plug can make backlog limit checks accept packets after the true queued backlog exceeds 4 GiB. This can allow the queue to grow beyond its configured limit and may drive the kernel into OOM, causing denial of service. For the CVSS the PR:L is used for the paranoid view because delegated CAP_NET_ADMIN or reduced capability administration may allow qdisc changes without full host root, while the realistic base case is PR:H. The issue is not directly network reachable as a standalone attack because reliable triggering requires qdisc configuration and a very large queued backlog. Impact is denial of service only. There is no evidence of memory corruption, information disclosure, or privilege escalation from this patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) YES REMOTE NETWORK SKB LOG LINUS QDISC PACKET LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 PrimitiveClass=NONE RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN 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 changed the score. 2. Signal breakdown Positive signals: * +1: Integer overflow / accounting bypass. The 32-bit backlog plus packet length calculation can wrap at 2^32 and make queue admission checks accept packets beyond the configured limit. * +1: Resource exhaustion / DoS. The queue can grow without bound after the wrap and the kernel can be driven to OOM. Negative or non-awarded signals: * Remote reachability not awarded. Packet traffic may fill the queue, but reliable triggering requires qdisc configuration and very large backlog conditions. * Local unprivileged trigger not awarded. The supplied text says reproduction requires root, and below-host-admin reachability is not established. * Host-admin penalty not applied. The text says root, but the exact host-vs-namespaced CAP_NET_ADMIN boundary is not fully resolved from the supplied context. * UAF / memory corruption not awarded. The patch shows arithmetic promotion to u64, not stale pointer use, OOB write, double free, or refcount corruption. * Confidentiality and integrity not awarded. The established consequence is resource exhaustion / OOM only. * Extra availability point not awarded. OOM / DoS is already counted once and no distinct persistent availability mechanism is established. * Manual-review escalation not awarded. This is a resource exhaustion issue without memory corruption, authorization bypass, COW violation, or unresolved lifetime primitive. 3. Reachability analysis The trigger requires configuring gred, bfifo, or plug qdisc with a limit near 4 GiB and then driving more than 4 GiB of queued traffic. The commit explicitly states that the bug can only be reproduced as root with a ridiculous setup. For qdisc configuration, CAP_NET_ADMIN is relevant, but the supplied evidence does not fully prove whether the complete trigger is host-admin-only or can be completed inside an attacker-created network namespace. Therefore HostAdminRequired is UNKNOWN and NamespaceScopedPrivilege is UNKNOWN. No ordinary unprivileged complete trigger is established. The vulnerable enqueue path is reached by traffic only after the qdisc has been configured. This is not a direct remote network attack because remote packets alone do not configure the required qdisc state. There is no special hardware requirement and no race condition. 4. Primitive and severity interpretation The exact primitive is a 32-bit integer wrap in queue backlog accounting. The wrapped value causes admission logic to misinterpret the true backlog and keep accepting packets after the real queue size exceeds the configured limit. This is not an active structured UAF, not fixed stale storage, and not a repeated release/refcount issue. There is no first lifetime operation, no dangling reference, and no second lifetime mutation. PrimitiveClass is NONE because the established bug is resource accounting / integer overflow leading to resource exhaustion, not kernel memory corruption or a security-boundary primitive. The demonstrated consequence is denial of service via kernel memory exhaustion / OOM. Speculative consequences beyond DoS are not supported by the patch. ImportantCandidate is NO because there is no unresolved corruption, ownership, authorization, or lifetime primitive. AutoDowngradeAllowed is YES because this can be handled as ordinary Moderate / Low-like resource exhaustion. 5. One-sentence report phrase A 32-bit backlog accounting wrap in gred, bfifo, and plug qdisc enqueue checks can bypass queue limits after very large queued backlog and drive kernel memory exhaustion, but exploitation requires privileged qdisc setup and no memory corruption or privilege escalation primitive is established. 6. Manual review recommendation NO MANUAL CHECK NEEDED Reason: the issue is a privileged or unresolved-privilege resource exhaustion bug with no UAF, no arbitrary write, no information leak, no authorization bypass, and no plausible Important-grade primitive from the supplied patch context. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net: sched: fix 32-bit backlog wrap in gred, bfifo and plug enqueue [ Upstream Commit: 3fb51b3960342bbee563543f8d33710fd0fb5a96 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3fb51b3960342bbee563543f8d33710fd0fb5a96 Changed files: net/sched/sch_fifo.c net/sched/sch_gred.c net/sched/sch_plug.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=3fb51b3960342bbee563543f8d33710fd0fb5a96 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-90109 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90109 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).