From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-72069][MODERATE 7.0] locking/rt: Fix the incorrect RCU protection in rt_spin_unlock() [ Upstream Date: Sat, 15 Aug 2026 21:47:47 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-72069 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: 3cfaac77b3c32ac3940df28866de263c3f45d24c List-Id: CVE: CVE-2026-72069 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: locking/rt: Fix the incorrect RCU protection in rt_spin_unlock() [ Upstream Commit: 3cfaac77b3c32ac3940df28866de263c3f45d24c Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3cfaac77b3c32ac3940df28866de263c3f45d24c Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72069 Analysis date: Sat, 15 Aug 2026 21:47:47 -0400 ActionableScore: 5 ActionableScore lower bound: 4 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A race in PREEMPT_RT spinlock and rwlock unlock paths can end RCU protection before the RT mutex unlock completes, allowing a local race to access a lock embedded in RCU freed memory and causing at least kernel crash with possible memory corruption concern. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-72069 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72069 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-2026-72069 MODERATE CHECK WITH IMPACT FROM ORIG NN LOW 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 the PREEMPT_RT spinlock and rwlock unlock paths can end RCU read side protection before the underlying RT mutex unlock operation is complete. If an object that embeds the lock is removed with RCU and freed after the grace period, a later rt_mutex_cmpxchg_release or slow unlock can access the lock inside already freed memory, creating a kernel use after free. For the CVSS the PR:L is used because a local user process may be able to reach affected kernel paths through subsystems that use RCU protected objects and RT locks, although reliable triggering depends on the concrete object type and timing window. The issue is not directly network reachable as a protocol input by itself. Impact is at least local denial of service via kernel crash and in the paranoid case may include confidentiality and integrity impact or privilege escalation because the primitive is a real UAF in kernel synchronization code.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5) YES LOCK DANGER 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 * Local unprivileged trigger: +1 syzbot found the issue and the affected primitive is a generic RT spinlock or rwlock path. A local process may reach affected kernel objects depending on subsystem usage. * Memory corruption, weak or race dependent UAF primitive: +1 The patch explicitly documents a UAF where an RCU freed object containing the lock can be accessed during `rt_mutex_cmpxchg_release()` or slow unlock. * Real lifetime corruption: +1 This is an RCU lifetime bug. RCU read side protection ends before the lock unlock operation is complete. * Reliable kernel crash / strong DoS: +1 Accessing a lock embedded in freed memory is a realistic kernel crash condition. * Weak LPE concern in paranoid score: +1 The stale access is not just a read. The unlock path can perform atomic updates on freed lock memory. No controlled reclaim or object replacement is shown, so this is not strong LPE evidence. * Hard or unreliable race: -1 Triggering requires a timing window involving RCU grace period completion and concurrent RT unlock. * PREEMPT_RT / RT lock substitution dependency: -1 The issue is specific to RT spinlock/rwlock substitutions, so exposure is narrower than generic mainline spinlock behavior. ## 3. Reachability analysis The bug is local, not directly network reachable. A local user process may trigger it indirectly through kernel paths that use RCU protected objects with embedded spinlocks or rwlocks on PREEMPT_RT kernels. Containers or namespaces may matter if they expose subsystem operations that create and destroy such objects, but the patch does not identify one specific unprivileged call path. The affected path is core locking code for RT kernels, but it requires PREEMPT_RT semantics and a race window, so practical reachability is configuration dependent. Call-site confidence: medium. The patch gives an explicit UAF interleaving in core locking code, but does not provide the concrete higher level subsystem object used by the syzbot reproducer. ## 4. Severity interpretation This is more than an ordinary Moderate because the patch explicitly fixes a kernel UAF in synchronization code. Realistic demonstrated impact is at least local DoS through a crash. Privilege escalation is plausible enough for manual review because the stale access occurs after RCU free and can touch freed lock memory, but there is no demonstrated attacker-controlled reclaim, type confusion, callback control, or arbitrary write primitive. Therefore the conservative score stays borderline, while the paranoid score reaches Actionable Moderate. ## 5. One-sentence report phrase A race in PREEMPT_RT spinlock and rwlock unlock paths can end RCU protection before the RT mutex unlock completes, allowing a local race to access a lock embedded in RCU freed memory and causing at least kernel crash with possible memory corruption concern. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: the patch explicitly documents a UAF in core RT locking code, and although exploitation beyond DoS is not proven, the lifetime corruption primitive is strong enough to avoid auto-closure. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: locking/rt: Fix the incorrect RCU protection in rt_spin_unlock() [ Upstream Commit: 3cfaac77b3c32ac3940df28866de263c3f45d24c Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3cfaac77b3c32ac3940df28866de263c3f45d24c Changed files: kernel/locking/spinlock_rt.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=3cfaac77b3c32ac3940df28866de263c3f45d24c ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-72069 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72069 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).