From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-46059][LOW] KVM: nSVM: Always use NextRIP as vmcb02's NextRIP after first L2 VMRUN Date: Wed, 27 May 2026 14:52:31 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-46059 X-AL-KERNEL-Priority: LOW X-AL-KERNEL-Severity: LOW X-AL-KERNEL-Base-Severity: LOW X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 2 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 3428ed1529a1af4cce5aff6c5bd2fcc39ad726bb List-Id: CVE: CVE-2026-46059 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: KVM: nSVM: Always use NextRIP as vmcb02's NextRIP after first L2 VMRUN Commit: 3428ed1529a1af4cce5aff6c5bd2fcc39ad726bb Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3428ed1529a1af4cce5aff6c5bd2fcc39ad726bb Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46059 Analysis date: Wed, 27 May 2026 14:52:31 -0400 ActionableScore: 2 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate / Low-like Manual review required: NO Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-46059 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46059 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: LOW Manual review required: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-46059 LOW 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:N/I:L/A:H';CWE-670;CWE-682;CWE-754;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.3';DESCR 'KVM nSVM can use the wrong NextRIP value for vmcb02 after the first L2 VMRUN when NRIPS is supported by hardware but not exposed to L1. This can corrupt nested guest control flow after save\/restore or similar nested state transitions and may cause L2 or L1 guest malfunction or denial of service. For the CVSS the PR:L is used because triggering requires access to KVM or control of a guest workload that can exercise nested virtualization, but not necessarily full host root where VM execution is delegated to users. The issue is not network reachable by itself and no host memory corruption primitive is supported by the patch context. Impact is mainly guest availability and possibly limited guest integrity, not host privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) MAYBE OOB DANGER VIRT HARDWARE LINUS DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 1. ActionableScore * Conservative score: 2 * Paranoid score: 2 * Final recommended bucket: **Ordinary Moderate / Low-like**:: 2. Signal breakdown * Local unprivileged trigger: +1. In deployments where `/dev/kvm` access is delegated, a local user able to run VMs may exercise nested SVM state. * Availability impact realistic: +1. Wrong `NextRIP` handling can break nested guest execution and cause L1 or L2 guest malfunction or DoS. * Broad/common subsystem: +1. KVM is widely deployed, though this specific path is nested AMD SVM. * Rare AND difficult-to-reach configuration: -1. Triggering requires nested SVM, NRIPS supported by hardware but not exposed to L1, soft interrupt injection, and save/restore or similar nested state transition. * Special conditions required: -1. This is not a natural packet or syscall crash path. It depends on a specific nested virtualization state sequence. * No memory corruption signal. The patch fixes architectural state selection, not UAF, OOB write, stale rmap, arbitrary write, or host memory lifetime corruption. 3. Reachability analysis The bug is reachable by a local actor with KVM access or by a guest workload that can exercise nested virtualization under an L1 hypervisor. Namespaces do not generally make this remotely reachable, but `/dev/kvm` access may be granted to non-root users in virtualization environments. The affected path is not network-triggerable and is not a default path for ordinary processes. Realistic exploitation is limited to nested virtualization correctness and guest DoS scenarios. 4. Severity interpretation This behaves like an ordinary Moderate or Low-like KVM correctness issue, not an Important-class vulnerability. Theoretical concern is incorrect nested guest control flow, but the patch does not support a host memory corruption, host privilege escalation, or guest-to-host escape primitive. Realistic impact is guest availability and possibly limited guest integrity within nested virtualization. 5. One-sentence report phrase Incorrect `NextRIP` selection in KVM nSVM after the first L2 `VMRUN` can corrupt nested guest control flow after save/restore and cause nested guest malfunction or DoS, without evidence of host memory corruption or privilege escalation. 6. Manual review recommendation NO MANUAL CHECK NEEDED. The issue is configuration-specific nested virtualization state corruption with no supported memory corruption, security-boundary bypass, or remote reachability. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: KVM: nSVM: Always use NextRIP as vmcb02's NextRIP after first L2 VMRUN Commit: 3428ed1529a1af4cce5aff6c5bd2fcc39ad726bb Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3428ed1529a1af4cce5aff6c5bd2fcc39ad726bb Commit description: For guests with NRIPS disabled, L1 does not provide NextRIP when running an L2 with an injected soft interrupt, instead it advances the current RIP before running it. KVM uses the current RIP as the NextRIP in vmcb02 to emulate a CPU without NRIPS. However, after L2 runs the first time, NextRIP will be updated by the CPU and/or KVM, and the current RIP is no longer the correct value to use in vmcb02. Hence, after save/restore, use the current RIP if and only if a nested run is pending, otherwise use NextRIP. Give soft_int_next_rip the same treatment, as it's the same logic, just for a narrower use case. Fixes: cc440cd ("KVM: nSVM: implement KVM_GET_NESTED_STATE and KVM_SET_NESTED_STATE") CC: stable@vger.kernel.org Signed-off-by: Yosry Ahmed Link: https://patch.msgid.link/20260225005950.3739782-6-yosry@kernel.org [sean: give soft_int_next_rip the same treatment] Signed-off-by: Sean Christopherson Signed-off-by: Greg Kroah-Hartman Changed files: arch/x86/kvm/svm/nested.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=3428ed1529a1af4cce5aff6c5bd2fcc39ad726bb ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-46059 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46059 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:N/I:N/A:L The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H The Best / paranoid CVSS score: 5.3 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: unknown Paranoid ActionableScore: 2 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: LOW KPANIC detected for this report: NO Published priority for this report (same as in Subject): LOW 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).