From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-52973][IMPORTANT] futex: Drop CLONE_THREAD requirement for private default hash alloc [ Upstream Date: Thu, 25 Jun 2026 16:35:25 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-52973 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: 6 X-AL-KERNEL-Commit: 1dcd36420af2da5bd59306dba9caf78e3d248b1d List-Id: CVE: CVE-2026-52973 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: futex: Drop CLONE_THREAD requirement for private default hash alloc [ Upstream Commit: 1dcd36420af2da5bd59306dba9caf78e3d248b1d Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1dcd36420af2da5bd59306dba9caf78e3d248b1d Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52973 Analysis date: Thu, 25 Jun 2026 16:35:25 -0400 ActionableScore: 8 ActionableScore lower bound: 6 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A local user can trigger a futex mm lifetime bug by using CLONE_VM without CLONE_THREAD, causing stale mm futex_ref accounting and a slab use after free in futex_hash_put with realistic DoS impact and plausible LPE concern. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-52973 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52973 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-2026-52973 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-362;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'An incorrect futex default hash allocation condition can leave an mm shared by CLONE_VM tasks without the expected private futex hash allocation. In that state mm futex_ref accounting can place a reference bias on a percpu counter that is no longer referenced by mm futex_ref, and later futex_hash_put can hit a slab use after free. A local user can potentially trigger this by creating CLONE_VM siblings that are not CLONE_THREAD and exercising futex lifetime paths while tasks exit. For the CVSS the PR:L is used because reliable triggering requires local code execution by an unprivileged user, not administrator level access. The issue is not network reachable. Impact is at least local denial of service via kernel crash. Because the primitive is a kernel use after free in futex reference accounting, the paranoid score treats privilege escalation as plausible and uses high confidentiality and integrity impact for manual review sensitivity.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8) MAYBE DANGER RACE UAF IMPROVEONLY LINUS KPANIC - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=8 ActionableScoreLower=6 ## 1. ActionableScore * Conservative score: 6 * Paranoid score: 8 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative signals: * Local unprivileged trigger: +1. A local process can use clone with CLONE_VM without CLONE_THREAD. * Generic memory corruption, strong corruption primitive: +2. The commit explicitly reports KASAN slab-use-after-free in futex_hash_put. * Real lifetime corruption: +1. The bug is a stale lifetime/reference accounting issue involving mm->futex_ref and percpu counters. * Reliable kernel crash / strong DoS: +1. The demonstrated symptom is a KASAN UAF and likely kernel crash. * Broad/default/common subsystem: +1. Futex and fork/clone/mm lifetime paths are core Linux kernel functionality. * Hard or unreliable race / special lifetime timing required: -1. Triggering depends on a specific CLONE_VM sharing pattern and task/mm teardown timing. Paranoid additional signals: * Privilege escalation plausible: +2. This is a kernel UAF in futex reference accounting, and futex/mm lifetime bugs are sensitive enough to require manual LPE review even though no controlled reclaim primitive is shown. * Confidentiality impact plausible: +1. Only in the paranoid interpretation, because successful exploitation of a kernel UAF may expose kernel or privileged process data. * Integrity impact plausible: +1. Only in the paranoid interpretation, because successful exploitation of a kernel UAF may corrupt kernel state. ## 3. Reachability analysis The bug is locally reachable by an unprivileged process that can create CLONE_VM siblings without CLONE_THREAD and exercise futex/mm lifetime paths during task exit. It is not network reachable. It does not require CAP_SYS_ADMIN or CAP_NET_ADMIN in the normal model, because clone and futex-related behavior are ordinary local process interfaces. Namespaces or containers do not remove concern, because the affected state is kernel mm/futex lifetime management and can still be reachable from contained local workloads unless blocked by sandbox policy. The path is broad and common, but reliable exploitation beyond crash likely requires careful timing and object lifetime control. ## 4. Severity interpretation This is above ordinary Moderate because the patch fixes a real kernel slab-use-after-free, not just a warning, leak, or NULL dereference. The realistic demonstrated impact is local DoS via kernel crash. The theoretical higher impact is local privilege escalation due to UAF in a core kernel subsystem, but the patch does not show an arbitrary write, controlled reclaim, or deterministic object confusion primitive. Therefore the conservative interpretation is Actionable Moderate, while the paranoid interpretation is a Strong Important candidate requiring manual review. ## 5. One-sentence report phrase A local user can trigger a futex mm lifetime bug by using CLONE_VM without CLONE_THREAD, causing stale mm futex_ref accounting and a slab use after free in futex_hash_put with realistic DoS impact and plausible LPE concern. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: confirmed kernel UAF in a broad futex/mm lifetime path, locally reachable without administrative privileges, with DoS demonstrated and privilege escalation plausible enough for Important-class manual triage. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: futex: Drop CLONE_THREAD requirement for private default hash alloc [ Upstream Commit: 1dcd36420af2da5bd59306dba9caf78e3d248b1d Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1dcd36420af2da5bd59306dba9caf78e3d248b1d Changed files: kernel/fork.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=1dcd36420af2da5bd59306dba9caf78e3d248b1d ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-52973 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52973 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: 6 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).