From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74439][MODERATE 7.0] iommu/vt-d: Clear Present bit before tearing down scalable-mode context entry [ Upstream Date: Sat, 15 Aug 2026 11:51:42 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74439 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: 7 X-AL-KERNEL-ActionableScore-Lower: 4 X-AL-KERNEL-Commit: e9e83bcfe37dc719182500dd823c03ab57d934f0 List-Id: CVE: CVE-2026-74439 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: iommu/vt-d: Clear Present bit before tearing down scalable-mode context entry [ Upstream Commit: e9e83bcfe37dc719182500dd823c03ab57d934f0 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e9e83bcfe37dc719182500dd823c03ab57d934f0 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74439 Analysis date: Sat, 15 Aug 2026 11:51:42 -0400 ActionableScore: 7 ActionableScore lower bound: 4 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74439 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74439 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-2026-74439 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-362;*CWE-416;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'VT-d scalable mode context teardown can clear the full 128-bit context entry while the Present bit is still set. During this window the IOMMU may fetch a torn entry or continue walking a stale entry that references freed PASID directory pages, which is a use-after-free candidate in the DMA translation path. For the CVSS the PR:L is used for the paranoid score because reliable triggering may be possible for a local actor with delegated device or VFIO or PASID management access, even if many deployments restrict this to administrators. The issue is not network reachable. Impact is at least local denial of service through IOMMU faults or device malfunction, and in the worst defensible case may affect confidentiality and integrity if stale DMA translation state can be abused.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 6) YES INIT UAF HARDWARE KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=7 ActionableScoreLower=4 1. ActionableScore * Conservative score: 4 * Paranoid score: 7 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: 2. Signal breakdown * Firmware-mediated external influence: +1. The IOMMU hardware can observe a torn or stale Present context entry during teardown. * Weak LPE concern: +1. A stale DMA translation context pointing at freed PASID structures could theoretically affect isolation, but no controlled exploit primitive is demonstrated. * Memory corruption, weak/indirect corruption candidate: +1. The bug is a stale freed-memory reference candidate in the IOMMU translation path, not a proven arbitrary write. * Real lifetime corruption: +1. PASID directory pages may be freed while hardware can still walk a Present entry. * Reliable kernel crash / strong DoS: +1. Spurious IOMMU faults, device malfunction, or unpredictable DMA behavior are realistic. * Privileged kernel/device-management memory corruption path: +1. The issue is in VT-d PASID/context teardown, a high-trust DMA isolation path. * Confidentiality impact plausible: +1 paranoid only. Stale translation state may theoretically expose memory through DMA isolation failure. * Integrity impact plausible: +1 paranoid only. Stale translation state may theoretically allow DMA writes outside intended mappings. * Hard or unreliable race / special timing required: -1. The issue depends on a teardown window and hardware fetching state at the wrong time. * Requires admin/root/CAP_* in typical deployments: -2 conservative. Device teardown and PASID/IOMMU management are normally privileged. This penalty is reduced in the paranoid score because VFIO, SVA, iommufd, or delegated device access may lower practical privileges. * Corruption primitive constrained or not directly attacker-controlled: -1 conservative. The patch does not show attacker-controlled reclaim, payload, or target selection. 3. Reachability analysis The typical trigger requires local control over device lifecycle, PASID teardown, VFIO/iommufd, SVA, or another device-management path. In ordinary deployments this is usually restricted to root or privileged services. In containerized or delegated-device environments, a reduced-privilege local actor may have enough device access to reach the path, which supports the paranoid PR:L interpretation. The issue is not network reachable. It depends on Intel VT-d scalable mode and PASID-related teardown behavior, so exposure is hardware and configuration dependent, but the affected path is security-sensitive because it protects DMA translation and device memory isolation. 4. Severity interpretation This is not an ordinary low-risk cleanup because the stale Present bit can let hardware walk freed PASID structures. Realistic impact is most clearly local DoS through IOMMU faults or device malfunction. Theoretical impact is higher because stale DMA translation state can affect confidentiality and integrity if a device or delegated device user can influence timing and memory reuse. No arbitrary code execution or strong LPE primitive is proven by the patch, so the conservative result remains Moderate, but the paranoid result is a Strong Important candidate for manual review. 5. One-sentence report phrase VT-d scalable-mode context teardown may leave Present set while PASID context memory is being cleared and later freed, allowing the IOMMU to observe stale or torn translation state with realistic DoS impact and plausible DMA isolation consequences. 6. Manual review recommendation MANUAL CHECK REQUIRED. The bug affects IOMMU/DMA translation lifetime rules and includes a stale freed PASID table walk candidate, so it should not be auto-closed even though practical exploitation is likely configuration dependent. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: iommu/vt-d: Clear Present bit before tearing down scalable-mode context entry [ Upstream Commit: e9e83bcfe37dc719182500dd823c03ab57d934f0 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e9e83bcfe37dc719182500dd823c03ab57d934f0 Changed files: drivers/iommu/intel/pasid.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=e9e83bcfe37dc719182500dd823c03ab57d934f0 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74439 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74439 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: 4 Paranoid ActionableScore: 7 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).