From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-64530][IMPORTANT] net/sched: cls_api: Handle TC_ACT_CONSUMED in tcf_qevent_handle [ Upstream Date: Sun, 26 Jul 2026 02:51:48 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-64530 X-AL-KERNEL-Priority: IMPORTANT X-AL-KERNEL-Severity: IMPORTANT X-AL-KERNEL-Base-Severity: IMPORTANT X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 8 X-AL-KERNEL-ActionableScore-Lower: 7 X-AL-KERNEL-Commit: 5ed3d6f85991656667059d3fa5a1d683ac58c447 List-Id: CVE: CVE-2026-64530 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: net/sched: cls_api: Handle TC_ACT_CONSUMED in tcf_qevent_handle [ Upstream Commit: 5ed3d6f85991656667059d3fa5a1d683ac58c447 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5ed3d6f85991656667059d3fa5a1d683ac58c447 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64530 Analysis date: Sun, 26 Jul 2026 02:51:48 -0400 ActionableScore: 8 ActionableScore lower bound: 7 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A UAF in net/sched qevent handling can occur when TC_ACT_CONSUMED is ignored and RED continues using an skb already consumed by act_ct defragmentation, allowing remote fragmented traffic to crash the kernel under affected tc configurations. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64530 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64530 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: IMPORTANT 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-2026-64530 IMPORTANT CHECK WITH IMPACT FROM ORIG NN IMPORTANT Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;CWE-703;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '8.1';DESCR 'A use-after-free can occur in the traffic control qevent path because tcf_qevent_handle() did not handle TC_ACT_CONSUMED returned by tcf_classify(). In this state the skb has been consumed by another component such as act_ct defragmentation for out-of-order fragments, but RED qdisc code may continue to enqueue, drop, or account the same skb. For the CVSS the PR:N is used for the paranoid score because a remote sender may only need network reachability once the vulnerable RED qevent and act_ct setup already exists. The issue is network reachable in deployments where such tc configuration is present and fragmented traffic can pass through the affected qdisc path. Impact is at least denial of service via kernel crash and in the worst case may allow confidentiality or integrity impact due to skb UAF memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8) YES REMOTE LEAK UAF NETWORK SKB KERNEL_PANIC_PLUS_UAF LINUS QDISC KPANIC YES NO guess ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=8 ActionableScoreLower=7 ## 1. ActionableScore * Conservative score: 7 * Paranoid score: 8 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown * Remote reachable / network-triggerable: +2 After the vulnerable RED qevent plus act_ct defrag configuration exists, fragmented out-of-order traffic can trigger the path remotely. * Generic memory corruption, strong corruption primitive: +2 The commit explicitly says RED continues operating on an skb it no longer owns, resulting in a UAF. * Real lifetime corruption: +1 This is an skb ownership and lifetime violation where TC_ACT_CONSUMED means the skb was consumed by another component. * Reliable kernel crash / strong DoS: +1 Continued enqueue/drop/accounting on a consumed skb is a credible kernel crash path. * Weak LPE concern: +1 conservative, +2 paranoid Conservative scoring treats this as weak LPE concern because no controlled reclaim or overwrite primitive is shown. Paranoid scoring raises this because skb UAF in a packet-processing path historically deserves manual review for possible exploitation beyond DoS. * Common networking / packet-processing path: +1 The bug is in net/sched traffic control packet handling, although the exact RED qevent plus act_ct setup is conditional. * Special configuration constraint: -1 conservative Triggering requires RED qevent, tc filter action ct, defrag behavior, and out-of-order fragments. This reduces default exposure but does not make the bug low risk. ## 3. Reachability analysis The bug can be triggered by traffic only when the affected qdisc and classifier/action setup is already configured. Creating that setup normally requires CAP_NET_ADMIN, but a remote sender may not need local privileges if the system already uses the vulnerable RED qevent plus act_ct configuration. Namespace delegation can matter because CAP_NET_ADMIN inside a delegated or containerized network namespace may allow non-host-root actors to configure similar paths. The path is not default-enabled in ordinary systems, but it is realistic in advanced traffic-control deployments. Call-site confidence: high. The commit identifies RED as the qdisc wiring qevents and describes the concrete red_enqueue continuation after TC_ACT_CONSUMED. ## 4. Severity interpretation This is not an ordinary Moderate resource leak or warning-only bug. It is an explicit skb UAF in a networking packet path with possible remote triggering under a specific but valid tc configuration. Realistic impact is at least DoS through kernel crash. Privilege escalation is not demonstrated, but the memory lifetime bug is strong enough to require manual analysis rather than auto-close. ## 5. One-sentence report phrase A UAF in net/sched qevent handling can occur when TC_ACT_CONSUMED is ignored and RED continues using an skb already consumed by act_ct defragmentation, allowing remote fragmented traffic to crash the kernel under affected tc configurations. ## 6. Manual review recommendation MANUAL CHECK REQUIRED The patch explicitly fixes a UAF in an skb lifetime path, and the trigger may be network-driven once the vulnerable traffic-control configuration exists. This should not be auto-closed. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net/sched: cls_api: Handle TC_ACT_CONSUMED in tcf_qevent_handle [ Upstream Commit: 5ed3d6f85991656667059d3fa5a1d683ac58c447 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5ed3d6f85991656667059d3fa5a1d683ac58c447 Changed files: net/sched/cls_api.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=5ed3d6f85991656667059d3fa5a1d683ac58c447 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64530 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64530 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:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 8.1 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: 7 Paranoid ActionableScore: 8 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: IMPORTANT KPANIC detected for this report: YES Published priority for this report (same as in Subject): IMPORTANT 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).