From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-53264][MODERATE 7.0] net/sched: act_api: use RCU with deferred freeing for action lifecycle [ Upstream Date: Thu, 25 Jun 2026 11:01:58 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-53264 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: 5 X-AL-KERNEL-ActionableScore-Lower: 4 X-AL-KERNEL-Commit: 98b2e40879abf0245be5a5b7af69e0f6ff524ac3 List-Id: CVE: CVE-2026-53264 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: net/sched: act_api: use RCU with deferred freeing for action lifecycle [ Upstream Commit: 98b2e40879abf0245be5a5b7af69e0f6ff524ac3 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=98b2e40879abf0245be5a5b7af69e0f6ff524ac3 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53264 Analysis date: Thu, 25 Jun 2026 11:01:58 -0400 ActionableScore: 5 ActionableScore lower bound: 4 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A race between concurrent tc `NEWTFILTER` and `DELFILTER` operations can free a `tc_action` while another path still holds an RCU-protected stale pointer, causing a kernel use-after-free and at least local DoS, with privilege-escalation risk requiring manual review. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53264 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53264 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-2026-53264 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-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in net sched action lifecycle can occur when NEWTFILTER and DELFILTER run concurrently. One path can find a tc_action through the IDR under RCU while another path drops the last reference, removes the action from the IDR, and frees the object immediately. The first path can then touch p tcfa_refcnt after kfree, creating a use after free on a kernel object. For the CVSS the PR:L value is used because reliable triggering requires local control of tc filter or action operations, typically CAP_NET_ADMIN, but this capability may be available to a local user through user and network namespaces or delegated container privileges. The issue is not directly network reachable through packet traffic and is triggered through local netlink control plane operations. Impact is at least local denial of service via kernel crash. In the paranoid interpretation, the UAF may allow broader memory corruption impact and possible privilege escalation, so manual review is required.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5) YES REMOTE DANGER INIT RACE UAF HARDWARE LINUS SYZBOT KPANIC NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=4 ## 1. ActionableScore * Conservative score: 4 * Paranoid score: 5 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown Triggered signals: * Memory corruption, weak primitive: +1 The patch explicitly fixes a UAF where `refcount_inc_not_zero(&p->tcfa_refcnt)` can run after `kfree(p)`. Because this is a race UAF without demonstrated reclaim, overwrite, callback dispatch, or type confusion, it is scored as weak primitive rather than strong primitive. * Real lifetime corruption: +1 This is an RCU lifetime bug. The object can be removed from the IDR and freed while another RCU-side path still holds a stale pointer. * Reliable kernel crash / strong DoS: +1 A stale pointer dereference on a freed `tc_action` object is a realistic kernel crash condition. * Local unprivileged or delegated trigger concern: +1 paranoid Direct triggering normally needs `CAP_NET_ADMIN`, but tc/netlink operations may be reachable inside user or network namespaces or delegated containers. * Local high-control netlink object lifecycle API: +1 paranoid The affected path uses tc netlink control operations where users can create and delete kernel networking objects and influence object lifetime. Subtractors: * Hard race / special timing required: -1 The bug requires concurrent `NEWTFILTER` and `DELFILTER` timing. * Requires `CAP_NET_ADMIN` in typical host deployments: -1 conservative Full `-2` is not used because namespace and container delegation can make this less than full host-root privilege in practical deployments. ## 3. Reachability analysis The bug is triggered through local tc/netlink control-plane operations, not by receiving network packets. In a normal host namespace, the attacker usually needs `CAP_NET_ADMIN` to create and delete filters or associated actions. In systems with unprivileged user namespaces, containers, or delegated network administration, a local user may obtain enough capability inside a network namespace to exercise the affected lifecycle path. The subsystem is common kernel networking infrastructure, but the vulnerable path is not a default passive network receive path. Exploitation requires racing action lookup and deletion, so reliability is lower than a straightforward OOB write or direct UAF with controlled reclaim. ## 4. Severity interpretation This is more than an ordinary Moderate because the patch fixes a concrete kernel UAF, not only a warning, leak, or validation issue. Realistic impact is most clearly local DoS through kernel crash. Practical privilege escalation is not demonstrated by the patch because there is no shown attacker-controlled reclaim, write-after-free, callback reuse, or type confusion. However, because this is a lifetime bug in a kernel networking object reachable through tc object lifecycle operations, it should not be auto-closed. Conservative handling: actionable borderline Moderate. Paranoid handling: Actionable Moderate at minimum, possible Important candidate after manual review. ## 5. One-sentence report phrase A race between concurrent tc `NEWTFILTER` and `DELFILTER` operations can free a `tc_action` while another path still holds an RCU-protected stale pointer, causing a kernel use-after-free and at least local DoS, with privilege-escalation risk requiring manual review. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: the patch explicitly fixes a UAF in kernel networking object lifetime management. Even though the race has no demonstrated reclaim or overwrite primitive, UAF bugs in tc/netlink lifecycle paths are historically security-relevant and should not be auto-closed. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net/sched: act_api: use RCU with deferred freeing for action lifecycle [ Upstream Commit: 98b2e40879abf0245be5a5b7af69e0f6ff524ac3 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=98b2e40879abf0245be5a5b7af69e0f6ff524ac3 Changed files: include/net/act_api.h net/sched/act_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=98b2e40879abf0245be5a5b7af69e0f6ff524ac3 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53264 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53264 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:L/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: 5 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).