From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-64073][MODERATE 7.0] irq_work: Fix use-after-free in irq_work_single() on PREEMPT_RT [ Upstream Date: Sun, 19 Jul 2026 19:27:09 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-64073 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: 2dc79362302922cb18f35e262712b5e58de65442 List-Id: CVE: CVE-2026-64073 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: irq_work: Fix use-after-free in irq_work_single() on PREEMPT_RT [ Upstream Commit: 2dc79362302922cb18f35e262712b5e58de65442 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2dc79362302922cb18f35e262712b5e58de65442 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64073 Analysis date: Sun, 19 Jul 2026 19:27:09 -0400 ActionableScore: 5 ActionableScore lower bound: 3 Actionable bucket: Actionable Moderate at minimum. Borderline Important candidate for PREEMPT_RT deployments Manual review required: YES Summary: A PREEMPT_RT irq_work lifetime race allows irq_work_sync() to return before irq_work_single() has finished accessing the work object, creating a local use-after-free that can crash the kernel and warrants manual review for possible exploitability. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64073 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64073 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-2026-64073 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:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A use-after-free race exists in irq_work on PREEMPT_RT because irq_work_sync can observe that IRQ_WORK_BUSY is cleared and return while irq_work_single still dereferences the same work object. A caller on another CPU may then free the object before irq_work_single finishes using it, which can lead to a kernel crash and may create a kernel memory corruption condition. For the CVSS the PR:L is used for the paranoid score because reliable triggering normally requires local code execution through a kernel subsystem that exposes an irq_work lifetime to a local user or service, but does not require full administrator privileges in the worst defensible interpretation. The issue is not directly network reachable. Impact is at least local denial of service and in the worst case may allow confidentiality or integrity impact due to use-after-free memory corruption. For the paranoid score, choose the highest still defensible interpretation supported by the bug class and patch context, with preference for manual-review sensitivity over autoclosed false negatives.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum. Borderline Important candidate for PREEMPT_RT deployments (with actual score 4) YES UAF HARDWARE LINUS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=3 ## 1. ActionableScore * Conservative score: 3 * Paranoid score: 5 * Final recommended bucket: **Actionable Moderate at minimum. Borderline Important candidate for PREEMPT_RT deployments**:: ## 2. Signal breakdown Triggered signals: * Local unprivileged trigger: +1 The bug is not a direct syscall interface, but it can plausibly be reached through local kernel subsystems that expose irq_work lifetime patterns to local users or services. * Memory corruption, weak primitive: +1 This is a real UAF, but it is a race-dependent stale access after BUSY is cleared. The patch does not show attacker-controlled reclaim, callback dispatch, type confusion, arbitrary write, or controlled object replacement. * Real lifetime corruption: +1 irq_work_sync() may return while irq_work_single() still accesses the same work object, allowing the caller to free it too early. * Reliable kernel crash / strong DoS: +1 A stale dereference of freed kernel memory can plausibly crash the kernel. * Broad/core kernel helper relevance: +1 in paranoid scoring irq_work is a core kernel mechanism used by multiple subsystems, although the affected path is PREEMPT_RT-specific. * Availability impact realistic: +1 in paranoid scoring If triggered, the likely impact is host-wide kernel crash or severe instability, not just a local task failure. Subtracting signals: * Hard or unreliable race / special timing required: -1 The exploitability depends on a precise interleaving between irq_work_single(), BUSY clearing, irq_work_sync(), and object free. * PREEMPT_RT-specific configuration: -1 in conservative scoring The affected behavior is specific to PREEMPT_RT non-HARD irq_work running through per-CPU kthreads. This is important in RT deployments but not universal across all Linux systems. Race-UAF downgrade applied: * No strong LPE bonus is awarded. * No confidentiality or integrity bonus is awarded for the conservative score. * Paranoid score is capped at 5 because the patch shows UAF lifetime corruption but not a demonstrated reclaim or write primitive. ## 3. Reachability analysis The issue is local, not network reachable. Triggering requires a code path where an irq_work item is queued, synchronized with irq_work_sync(), and then freed while PREEMPT_RT executes non-HARD irq_work in run_irq_workd(). A fully remote attacker cannot directly reach this path from the patch context. Namespaces and containers may matter if an untrusted workload can exercise a subsystem that uses irq_work and exposes the vulnerable lifetime pattern, but the patch does not identify such a direct unprivileged interface. PREEMPT_RT is deployment-specific. On RT kernels this is more relevant because the affected execution model is part of normal operation. Call-site confidence: medium. The patch clearly shows the lifetime bug inside irq_work synchronization, but the input does not include concrete external call sites showing a reliable user-controlled trigger. ## 4. Severity interpretation This behaves more like an actionable Moderate than an ordinary Moderate because it is a real kernel UAF lifetime race in a core helper. It is not enough for a Strong Important classification on conservative scoring because the patch does not show attacker-controlled reclaim, stale callback execution, write-after-free, type confusion, or refcount takeover. Theoretical memory corruption potential exists because freed kernel memory is accessed after irq_work_sync() may allow object release. Realistic exploitation evidence is weaker and points primarily to local DoS unless a reachable subsystem provides controlled timing and object reuse. ## 5. One-sentence report phrase A PREEMPT_RT irq_work lifetime race allows irq_work_sync() to return before irq_work_single() has finished accessing the work object, creating a local use-after-free that can crash the kernel and warrants manual review for possible exploitability. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: this is a real kernel UAF race in core irq_work lifetime handling. Even though the demonstrated primitive is weak and race-dependent, UAF bugs should not be auto-closed without checking reachable call sites and whether any local subsystem gives attackers enough control over object lifetime or reclaim. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: irq_work: Fix use-after-free in irq_work_single() on PREEMPT_RT [ Upstream Commit: 2dc79362302922cb18f35e262712b5e58de65442 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2dc79362302922cb18f35e262712b5e58de65442 Changed files: kernel/irq_work.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=2dc79362302922cb18f35e262712b5e58de65442 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64073 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64073 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: 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).