From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-46082][MODERATE REGULAR] KVM: SVM: Inject #UD for INVLPGA if EFER.SVME=0 Date: Fri, 07 Aug 2026 10:09:44 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-46082 X-AL-KERNEL-Priority: MODERATE REGULAR X-AL-KERNEL-Severity: MODERATE REGULAR X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 4 X-AL-KERNEL-ActionableScore-Lower: 3 X-AL-KERNEL-Commit: 3ac9d4241d205f5d0df06358349ca718ebb0fa12 List-Id: CVE: CVE-2026-46082 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: KVM: SVM: Inject #UD for INVLPGA if EFER.SVME=0 Commit: 3ac9d4241d205f5d0df06358349ca718ebb0fa12 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3ac9d4241d205f5d0df06358349ca718ebb0fa12 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46082 Analysis date: Fri, 07 Aug 2026 10:09:44 -0400 ActionableScore: 4 ActionableScore lower bound: 3 Actionable bucket: Borderline, manual review recommended Manual review required: YES Summary: KVM SVM handled INVLPGA without checking EFER.SVME, allowing a guest to reach invalid virtualization-instruction emulation instead of receiving the architecturally required UD exception, with likely impact limited to availability or virtualization correctness. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-46082 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46082 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 REGULAR 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-2026-46082 MODERATE CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-754;CWE-284;CWE-693;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'KVM SVM handled INVLPGA without first checking whether nested SVM execution was permitted when EFER.SVME was clear. A guest could execute INVLPGA in a state where AMD architecture requires a UD exception, causing KVM to emulate a privileged virtualization instruction instead of rejecting it. For the CVSS the PR:L is used in the paranoid score because a guest user or tenant that can run code in a VM may be able to trigger the intercept without host administrator privileges. The issue is not network reachable and is triggered from guest code through the virtualization control path. Impact is mainly availability and isolation correctness, with no evidence of memory corruption or a direct host privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 4) SKIP CVE-2026-46082 SKIP The Fixes patch not applied yet, so unlikely that actual: ff092385e828 YES NO NO unknown MAYBE OOB VIRT SIMPLEFIX HARDWARE LINUS DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=3 ## 1. ActionableScore * Conservative score: 3 * Paranoid score: 4 * Final recommended bucket: **Borderline, manual review recommended**:: ## 2. Signal breakdown * Local or guest-controlled trigger: +1 A guest that can execute relevant code paths can issue INVLPGA and reach the KVM SVM interception path. * Cross-boundary isolation or policy correctness concern: +1 KVM handled a virtualization instruction when AMD architecture requires #UD if EFER.SVME=0. This is a guest-to-host emulation correctness boundary issue, but not a demonstrated host compromise primitive. * Availability or VM correctness impact plausible: +1 Incorrect handling of INVLPGA may affect guest execution or TLB-related virtualization behavior. The patch does not show a host UAF, OOB access, arbitrary write, or kernel panic path. * Broad virtualization subsystem exposure: +1 in paranoid score only KVM SVM is a security-sensitive virtualization boundary on AMD systems, so manual review is justified even though the concrete primitive is weak. No memory corruption, UAF, rmap/SPTE lifetime issue, page-cache corruption, or LPE primitive is shown by the patch. ## 3. Reachability analysis The bug is triggerable from guest execution, not from the network. The attacker normally needs the ability to run code in a KVM guest on an AMD SVM host, and possibly guest-kernel or nested-virtualization-level control depending on how INVLPGA reaches the intercept path. This does not require host root, but it is also not a normal unprivileged host-local syscall interface. Containers and namespaces on the host do not materially lower the privilege requirement unless they provide access to create or control KVM guests. ## 4. Severity interpretation This behaves more like a borderline Moderate KVM correctness issue than an Important-class vulnerability. The theoretical concern is that KVM incorrectly emulates a privileged virtualization instruction across a guest-host boundary. The realistic evidence from the patch supports incorrect exception injection and possible availability or isolation-correctness impact, but not memory corruption or privilege escalation. ## 5. One-sentence report phrase KVM SVM handled INVLPGA without checking EFER.SVME, allowing a guest to reach invalid virtualization-instruction emulation instead of receiving the architecturally required UD exception, with likely impact limited to availability or virtualization correctness. ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED Manual review is recommended because this is guest-triggerable KVM behavior across a virtualization boundary, but the patch does not show a concrete memory corruption or host privilege escalation primitive. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: KVM: SVM: Inject #UD for INVLPGA if EFER.SVME=0 Commit: 3ac9d4241d205f5d0df06358349ca718ebb0fa12 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3ac9d4241d205f5d0df06358349ca718ebb0fa12 Commit description: INVLPGA should cause a #UD when EFER.SVME is not set. Add a check to properly inject #UD when EFER.SVME=0. Fixes: ff09238 ("KVM: SVM: Implement INVLPGA") Cc: stable@vger.kernel.org Signed-off-by: Kevin Cheng Reviewed-by: Yosry Ahmed Link: https://patch.msgid.link/20260228033328.2285047-3-chengkev@google.com [sean: tag for stable@] Signed-off-by: Sean Christopherson Signed-off-by: Greg Kroah-Hartman Changed files: arch/x86/kvm/svm/svm.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=3ac9d4241d205f5d0df06358349ca718ebb0fa12 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-46082 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46082 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:L/PR:L/UI:N/S:U/C:N/I:N/A:L The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 5.5 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: 4 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 REGULAR 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).