From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-46173][IMPORTANT] exit: prevent preemption of oopsing TASK_DEAD task Date: Thu, 28 May 2026 10:58:54 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-46173 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: 9 X-AL-KERNEL-ActionableScore-Lower: 7 X-AL-KERNEL-Commit: 640b4c00fb0e2920327435f6176cbefc3c546165 List-Id: CVE: CVE-2026-46173 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: exit: prevent preemption of oopsing TASK_DEAD task Commit: 640b4c00fb0e2920327435f6176cbefc3c546165 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=640b4c00fb0e2920327435f6176cbefc3c546165 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46173 Analysis date: Thu, 28 May 2026 10:58:54 -0400 ActionableScore: 9 ActionableScore lower bound: 7 Actionable bucket: High-end Important / possible Critical candidate Manual review required: YES Summary: An exiting task that oopses could enter `do_task_dead()` with preemption enabled, allowing a `TASK_DEAD` task stack to be freed or reused while still runnable, leading to task-stack UAF or double-free and possible local privilege escalation. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-46173 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46173 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-2026-46173 IMPORTANT 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-415;CWE-362;CWE-667;BEST CVSS score: '7';DESCR 'make_task_dead could call do_task_dead with preemption enabled when an already exiting task hit an oops. If the TASK_DEAD task is preempted before it explicitly enters the scheduler, finish_task_switch can treat its stack as no longer needed while the task can still run, leading to task stack use-after-free or double-free. For the CVSS the PR:L is used because a local user may trigger an oops through a reachable kernel release or exit path without full administrative privileges, but reliable exploitation requires a special oops during task exit timing condition. The issue is not network reachable. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality and integrity impact because two tasks may end up running on the same stack.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is High-end Important / possible Critical candidate (with actual score 9) MAYBE UAF LINUS KPANIC - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=9 ActionableScoreLower=7 ## 1. ActionableScore * Conservative score: 7 * Paranoid score: 9 * Final recommended bucket: **High-end Important / possible Critical candidate**:: ## 2. Signal breakdown Conservative signals: * Local unprivileged trigger: +1. A local user may be able to trigger an oops through a reachable kernel path during task exit. * Generic memory corruption: +2. The patch describes task stack use-after-free and double-free. * Real lifetime corruption: +1. A `TASK_DEAD` task can be preempted while the scheduler assumes its stack is no longer usable. * Reliable kernel crash / strong DoS: +1. Stack lifetime corruption can crash or destabilize the kernel. * Broad/default subsystem: +1. This is core task exit and scheduler interaction, not a niche driver. * Hard timing / special condition: -1. Exploitation requires an oops during task exit and preemption at the wrong point. * Weak-to-strong LPE concern: +2. Reuse or double-free of a whole task stack is a strong corruption primitive if an attacker can shape the oops and timing. Paranoid additional signals: * Confidentiality impact plausible: +1. Two tasks sharing or reusing a stack can expose kernel stack contents. * Integrity impact plausible: +1. Task stack reuse can corrupt control/data state and may support privilege escalation. ## 3. Reachability analysis The trigger is local. The attacker needs a way to cause a kernel oops while a task is already exiting, for example through a reachable `file_operations::release` or similar exit-time path. This is not network reachable by itself. Namespaces and containers may matter because many container workloads can create and exit processes and exercise kernel release paths, but the key requirement is still finding an oopsable path during exit. The bug is in core kernel exit/scheduler logic and therefore has broad impact once the trigger condition is met. ## 4. Severity interpretation This behaves like an Important to possible Critical candidate, not an ordinary Moderate. The realistic minimum impact is local DoS via kernel crash. The higher-impact concern is justified because the patch explicitly describes use-after-free or double-free of the entire task stack and even two tasks running on the same stack. The exploitability is constrained by the need for a suitable oops during task exit, so this is not automatically a reliable LPE. But the primitive is strong enough that it should not be auto-closed. ## 5. One-sentence report phrase An exiting task that oopses could enter `do_task_dead()` with preemption enabled, allowing a `TASK_DEAD` task stack to be freed or reused while still runnable, leading to task-stack UAF or double-free and possible local privilege escalation. ## 6. Manual review recommendation MANUAL CHECK REQUIRED This is core-kernel task stack lifetime corruption with explicit UAF/double-free consequences. Even though the trigger requires a special oops-during-exit condition, the corruption primitive is strong and security-relevant. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: exit: prevent preemption of oopsing TASK_DEAD task Commit: 640b4c00fb0e2920327435f6176cbefc3c546165 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=640b4c00fb0e2920327435f6176cbefc3c546165 Commit description: When an already-exiting task oopses, make_task_dead() currently calls do_task_dead() with preemption enabled. That is forbidden: do_task_dead() calls __schedule(), which has a comment saying "WARNING: must be called with preemption disabled!". If an oopsing task is preempted in do_task_dead(), between becoming TASK_DEAD and entering the scheduler explicitly, bad things happen: finish_task_switch() assumes that once the scheduler has switched away from a TASK_DEAD task, the task can never run again and its stack is no longer needed; but that assumption apparently doesn't hold if the dead task was preempted (the SM_PREEMPT case). This means that the scheduler ends up repeatedly dropping references on the dead task's stack, which can lead to use-after-free or double-free of the entire task stack; in other words, two tasks can end up running on the same stack, resulting in various kinds of memory corruption. (This does not just affect "recursively oopsing" tasks; it is enough to oops once during task exit, for example in a file_operations::release handler) Fixes: 7f80a2f ("exit: Stop poorly open coding do_task_dead in make_task_dead") Cc: stable@kernel.org Signed-off-by: Jann Horn Acked-by: Peter Zijlstra Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman Changed files: kernel/exit.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=640b4c00fb0e2920327435f6176cbefc3c546165 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-46173 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46173 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: Not available 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: 7 Paranoid ActionableScore: 9 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).