From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-53011][MODERATE 7.0] net/sched: taprio: fix use-after-free in advance_sched() on schedule switch [ Upstream Date: Wed, 24 Jun 2026 14:53:32 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-53011 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 7 X-AL-KERNEL-ActionableScore-Lower: 4 X-AL-KERNEL-Commit: a8fc396519ef4f081bc545e88f61241728bb78d7 List-Id: CVE: CVE-2026-53011 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: net/sched: taprio: fix use-after-free in advance_sched() on schedule switch [ Upstream Commit: a8fc396519ef4f081bc545e88f61241728bb78d7 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a8fc396519ef4f081bc545e88f61241728bb78d7 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53011 Analysis date: Wed, 24 Jun 2026 14:53:32 -0400 ActionableScore: 7 ActionableScore lower bound: 4 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A use-after-free in the taprio qdisc schedule switch path can leave `next` pointing into an old RCU-freed oper schedule, allowing a stale `sched_entry` write and publication as `current_entry`, with realistic local DoS impact and a defensible worst-case concern for privilege escalation in delegated CAP_NET_ADMIN environments. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53011 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53011 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 7.0 Manual review required: YES A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-53011 MODERATE CHECK Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A use after free in the taprio qdisc schedule switch path occurs because advance_sched can keep next pointing to an entry from the old oper schedule after switch_schedules queues that old schedule for RCU freeing. The stale entry is then written through next end_time and published as q current_entry, creating a kernel memory corruption candidate rather than a pure warning. For the CVSS the PR:L is used for the paranoid score because taprio setup normally needs CAP_NET_ADMIN, but this capability can be delegated to a container root or network management service account rather than full host root. The issue is not directly network reachable and is triggered through local control plane qdisc configuration, not by remote packet traffic. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to the UAF write and stale pointer reuse, so manual review is needed.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 6) YES REMOTE UAF NETWORK KPANIC KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=7 ActionableScoreLower=4 ## 1. ActionableScore * Conservative score: 4 * Paranoid score: 7 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative signals: * Generic memory corruption: +2. The patch explicitly fixes a use-after-free where `next` still points into the old oper schedule after `switch_schedules()` queues it for RCU freeing. * Real lifetime corruption: +1. This is an RCU lifetime bug with a stale pointer surviving a schedule switch. * Reliable kernel crash / strong DoS: +1. A stale `sched_entry` is written and then published as `q->current_entry`, which is a credible kernel crash path. * Weak LPE concern: +1. There is a write through a stale pointer, but no demonstrated attacker-controlled reclaim or controlled overwrite target. * Requires CAP_NET_ADMIN in typical deployments: -2. Configuring taprio qdisc and admin schedules normally requires network administration privileges. * Corruption primitive constrained: -1. The written value is an `end_time` derived by kernel scheduling logic, not an arbitrary attacker-controlled payload. * Broad kernel networking control-plane exposure: +1. `net/sched` is a common kernel networking subsystem, although taprio itself is specialized. Paranoid additions / interpretation: * Local unprivileged trigger: +1. In environments with unprivileged user namespaces or delegated network administration, CAP_NET_ADMIN may be available inside a namespace or to a reduced-privilege service account. * Confidentiality impact plausible: +1. Because this is a kernel UAF with stale pointer publication, limited information impact cannot be ruled out without manual object-lifetime review. * Integrity impact plausible: +1. The stale object is written through and reused as `current_entry`, making integrity impact plausible in a worst-case review model. * No full admin penalty in paranoid mode. Delegated CAP_NET_ADMIN is not equivalent to full host root in practical risk terms. ## 3. Reachability analysis The bug is triggered through local control-plane configuration of the taprio qdisc and schedule switching, not through remote packet traffic. In normal host deployments, the attacker needs CAP_NET_ADMIN to configure taprio schedules, so the conservative reachability is privileged local. In containerized or namespace-enabled deployments, CAP_NET_ADMIN may be delegated to container root or a network management service account, which supports the paranoid PR:L style interpretation. The affected path is not default packet processing and requires taprio to be configured, but it is still reachable through standard Linux traffic-control interfaces when the qdisc is available. ## 4. Severity interpretation This is stronger than an ordinary Moderate because the patch fixes an explicit UAF with a stale pointer write and later pointer publication. Realistic exploitation evidence points first to local DoS or kernel crash, because the overwrite value and target are constrained and no attacker-controlled reclaim primitive is shown. The paranoid interpretation treats it as an Important candidate because kernel UAF plus write-after-free in a delegated CAP_NET_ADMIN path can sometimes become exploitable after deeper manual analysis. ## 5. One-sentence report phrase A use-after-free in the taprio qdisc schedule switch path can leave `next` pointing into an old RCU-freed oper schedule, allowing a stale `sched_entry` write and publication as `current_entry`, with realistic local DoS impact and a defensible worst-case concern for privilege escalation in delegated CAP_NET_ADMIN environments. ## 6. Manual review recommendation MANUAL CHECK REQUIRED This should not be auto-closed because it is an explicit kernel UAF with stale pointer write and RCU lifetime involvement, even though the practical trigger usually requires CAP_NET_ADMIN and the demonstrated impact is primarily DoS. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net/sched: taprio: fix use-after-free in advance_sched() on schedule switch [ Upstream Commit: a8fc396519ef4f081bc545e88f61241728bb78d7 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a8fc396519ef4f081bc545e88f61241728bb78d7 Changed files: net/sched/sch_taprio.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=a8fc396519ef4f081bc545e88f61241728bb78d7 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53011 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53011 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:L/I:L/A:H The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 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: 4 Paranoid ActionableScore: 7 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: YES Published priority for this report (same as in Subject): MODERATE 7.0 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).