From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-64424][MODERATE 7.0] netpoll: fix a use-after-free on shutdown path Date: Sat, 25 Jul 2026 14:04:46 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-64424 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 5 X-AL-KERNEL-ActionableScore-Lower: 3 X-AL-KERNEL-Commit: 95ecc5b58042f6b6743b589e6588f1cd7ba336aa List-Id: CVE: CVE-2026-64424 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: netpoll: fix a use-after-free on shutdown path Commit: 95ecc5b58042f6b6743b589e6588f1cd7ba336aa Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=95ecc5b58042f6b6743b589e6588f1cd7ba336aa Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64424 Analysis date: Sat, 25 Jul 2026 14:04:46 -0400 ActionableScore: 5 ActionableScore lower bound: 3 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A race in the netpoll shutdown path can leave delayed TX work running after `netpoll_info` is freed, causing a KASAN-confirmed use-after-free and at least a local kernel crash, with weak but review-worthy privilege-escalation concern due to asynchronous freed-object access. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64424 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64424 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-2026-64424 MODERATE CHECK WITH IMPACT FROM ORIG NN MODERATE 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:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A use-after-free can occur in the netpoll shutdown path when delayed TX work keeps running while netpoll_info is being released through RCU cleanup. The worker reaches the freed object through its embedded work item and can touch the freed TX queue after kfree, which is a kernel memory corruption condition and at least a crashable DoS. For the CVSS the PR:L is used for the paranoid score because a reduced capability local actor with delegated network or device administration may be able to trigger cleanup paths in some deployments, while the base case is closer to administrator controlled netpoll or netconsole teardown. The issue is not directly network reachable because the vulnerable window is in shutdown cleanup rather than packet receive processing. Impact is at least local denial of service via kernel crash and in the worst defensible case may include confidentiality or integrity impact due to UAF based memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 4) YES REMOTE READ DANGER UAF SKB LINUS INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=3 ## 1. ActionableScore * Conservative score: 3 * Paranoid score: 5 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative signals: * Memory corruption, weak primitive: +1 The patch fixes a real KASAN-detected slab-use-after-free, but it is race-dependent and no attacker-controlled reclaim or replacement object is shown. * Real lifetime corruption: +1 `netpoll_info` can be freed via RCU while delayed TX work still reaches it through the embedded work item. * Reliable kernel crash / strong DoS: +1 KASAN shows a concrete UAF in `queue_process()` via `skb_dequeue()`, making kernel crash realistic. * Hard or unreliable race / special timing required: -1 Triggering requires overlap between netpoll cleanup and pending TX work. * Requires admin/root/CAP-style control in typical deployments: -1 Netpoll/netconsole setup and shutdown are usually administrator-controlled, but reduced-capability service or delegated network-management contexts may exist, so I do not apply the full -2 in the practical triage score. * Privileged kernel/device-management lifetime path: +1 The bug is in a shutdown/cleanup path tied to network device emergency logging and delayed work lifetime. Paranoid additional interpretation: * Weak LPE concern: +1 The worker accesses a freed object asynchronously and `skb_dequeue()` can interact with queue metadata after free. No reclaim primitive is demonstrated, so this is weak concern only, not strong LPE plausibility. Paranoid cap applied: * This is a race-dependent UAF without demonstrated attacker-controlled reclaim, callback control, type confusion, or arbitrary write. Per the race-UAF downgrade rule, the conservative score should not be treated as Important solely from bug class, and the paranoid score is capped at 5. ## 3. Reachability analysis The issue is not directly network-triggerable. It occurs in the netpoll shutdown path when `__netpoll_cleanup()` clears `dev->npinfo`, schedules RCU cleanup, and pending delayed TX work can still run afterward. Typical triggering requires local administrative control over netpoll or netconsole configuration, device teardown, module unload, or network device shutdown paths. In containerized or appliance environments, a reduced-capability root, service account, or delegated network-management component might influence these paths, which supports the paranoid PR:L-style interpretation but not a true remote or unprivileged default trigger. Netpoll/netconsole is not a default common packet-processing path. Realistic exploitation depends on netpoll being configured and on winning a shutdown race with queued TX work. Call-site confidence: high. The commit message gives the failing call trace, allocation/free path, and the exact delayed work versus RCU cleanup lifetime mismatch. ## 4. Severity interpretation This is more than an ordinary Moderate correctness fix because it is a confirmed kernel UAF in asynchronous workqueue lifetime management. Realistic demonstrated impact is local DoS through kernel crash. At the same time, the patch does not show attacker-controlled reclaim, object replacement, callback dispatch, or arbitrary write. Therefore, practical privilege escalation is not strongly demonstrated. The best handling is Actionable Moderate at minimum, with manual review recommended because UAF lifetime bugs are often under-scored during early triage. ## 5. One-sentence report phrase A race in the netpoll shutdown path can leave delayed TX work running after `netpoll_info` is freed, causing a KASAN-confirmed use-after-free and at least a local kernel crash, with weak but review-worthy privilege-escalation concern due to asynchronous freed-object access. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: this is a real kernel UAF, not just a warning or resource leak. Even though the demonstrated impact is DoS and exploitation appears race-dependent and usually privileged, the asynchronous workqueue access to freed network state should not be auto-closed without human review. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: netpoll: fix a use-after-free on shutdown path Commit: 95ecc5b58042f6b6743b589e6588f1cd7ba336aa Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=95ecc5b58042f6b6743b589e6588f1cd7ba336aa Commit description: There is a use-after-free error on netpoll, which is clearly detected by KASAN. BUG: KASAN: slab-use-after-free in _raw_spin_lock_irqsave+0x3b/0x80 Read of size 1 at addr ... by task kworker/9:1 Workqueue: events queue_process Call Trace: skb_dequeue+0x1e/0xb0 queue_process+0x2c/0x600 process_scheduled_works+0x4b6/0x850 worker_thread+0x414/0x5a0 Allocated by task 242: __netpoll_setup+0x201/0x4a0 netpoll_setup+0x249/0x550 enabled_store+0x32f/0x380 Freed by task 0: kfree+0x1b7/0x540 rcu_core+0x3f8/0x7a0 The problem happens when there is a pending TX worker running in parallel with the cleanup path. This is what happens on netpoll shutdown path: 1) __netpoll_cleanup() is called 2) set dev->npinfo to NULL 3) call_rcu() with rcu_cleanup_netpoll_info() 3.1) rcu_cleanup_netpoll_info() tries to cancel all workers with cancel_delayed_work(), but doesn't wait for the worker to finish 4) and kfree(npinfo); Because 3.1) doesn't really cancel the work, as the comment says "we can't call cancel_delayed_work_sync here, as we are in softirq", the TX worker can run after 4). Tl;DR: queue_process() is not an RCU reader, it reaches npinfo through the work item via container_of(). Use disable_delayed_work_sync() to ensure the worker is completely stopped and prevent any future re-arming attempts. Once npinfo is set to NULL, senders will bail out and not queue new work. The disable flag ensures any in-flight re-arming attempts also fail silently. In the future, we can do the cleanup inline here without needing the npinfo->rcu rcu_head, but that is net-next material. Cc: stable@vger.kernel.org Fixes: 38e6bc1 ("netpoll: make __netpoll_cleanup non-block") Reviewed-by: Pavan Chebbi Signed-off-by: Breno Leitao Link: https://patch.msgid.link/20260625-netpoll_rcu_fix-v2-1-0748ffac1e98@debian.org Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman Changed files: net/core/netpoll.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=95ecc5b58042f6b6743b589e6588f1cd7ba336aa ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64424 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64424 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: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: 3 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: NO 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).