{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-99178", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-09-25T10:25:14.399Z", "datePublished": "2026-10-28T10:35:31.961Z", "dateUpdated": "2026-11-01T12:42:11.076Z"}, "containers": {"cna": {"providerMetadata": {"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-11-01T12:42:11.076Z"}, "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nx86/kvm: Don't consume async #PF flags on a kernel #PF in NMI context\n\nAn async #PF \"page not present\" event arrives through the #PF vector,\nand its reason sits in the per-CPU apf_reason.flags until\n__kvm_handle_async_pf() reads and clears it. If an NMI arrives after\nthe event is injected and before the #PF handler reads the flags, and\nthe NMI handler itself takes a #PF, that fault reads and clears the\nflags belonging to the #PF it interrupted. It then finds interrupts\ndisabled in the NMI context it interrupted, and panics:\n\n Kernel panic - not syncing: Host injected async #PF in interrupt\ndisabled region\n Call Trace:\n <NMI>\n panic+0x52/0x60\n __kvm_handle_async_pf+0xb0/0xb0\n exc_page_fault+0x71/0xb0\n asm_exc_page_fault+0x27/0x30\n RIP: 0010:__get_user_nocheck_8+0x6/0x20\n perf_callchain_user+0x147/0x1a0\n get_perf_callchain+0x12d/0x1c0\n ...\n perf_event_nmi_handler+0x26/0x50\n exc_nmi+0xe8/0x110\n RIP: 0010:asm_exc_page_fault+0x0/0x30\n </NMI>\n\nThe last RIP line shows the NMI landing on the first instruction of\nthe #PF entry. perf with user call chains takes such a fault: the\nsampling NMI walks the user stack with __get_user(), which faults when\na saved frame pointer is not a valid user address or the walk runs off\nthe top of the stack. The same window exists when KVM, running as an\nL1 hypervisor with DELIVERY_AS_PF_VMEXIT, reads the flags itself after\na #PF VM-exit.\n\nThe NMI entry code saves and restores CR2 for this nesting, but not the\nasync #PF reason. Andy Lutomirski described the race, with perf as the\nexample, when async #PF delivery was reworked in 2020 [1]. Saving and\nclearing the flags across the NMI, next to CR2, was discussed there but\nnot merged.\n\nSince that rework, Linux has stopped setting KVM_ASYNC_PF_SEND_ALWAYS,\nso the host delivers \"page not present\" only for user mode faults and\na kernel-mode fault in NMI context (including kernel-mode #MC and #DB)\ncannot be an async page fault. In that case, return without touching\nthe flags so that the interrupted handler finds them intact.\n\nTested on v7.3-rc5 in a 4-vCPU, 2 GiB guest restored from a snapshot\nwhose memory is served on demand through userfaultfd, so that reading\nit back takes async #PFs, while every thread samples hardware cycles\nwith user call chains and points its frame pointer at an unmapped page.\nWithout this patch the guest panicked as above in 3 of 3 runs. With it,\nthe guest survived 3 of 3 runs of 60 seconds, and the host counted\n148,441 to 153,334 kvm_async_pf_not_present events in the first 20\nseconds of each. On 6.18.50 the results were the same: the guest\npanicked without the patch and survived with it."}], "affected": [{"product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["arch/x86/kernel/kvm.c"], "versions": [{"version": "631bc4878220932fe67fc46fc7cf7cccdb1ec597", "lessThan": "fd60b32a99627fda479c9fa1d4a82fa9f7994670", "status": "affected", "versionType": "git"}, {"version": "631bc4878220932fe67fc46fc7cf7cccdb1ec597", "lessThan": "b77e9622bbade9812e2090c66d25c372f515e921", "status": "affected", "versionType": "git"}, {"version": "631bc4878220932fe67fc46fc7cf7cccdb1ec597", "lessThan": "f45ee1ff6358a22d7e22a4c53cb3148ea97b10d9", "status": "affected", "versionType": "git"}, {"version": "631bc4878220932fe67fc46fc7cf7cccdb1ec597", "lessThan": "81d99abe2bd81379abfb595e403bbbee6fbfc624", "status": "affected", "versionType": "git"}]}, {"product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["arch/x86/kernel/kvm.c"], "versions": [{"version": "2.6.38", "status": "affected"}, {"version": "0", "lessThan": "2.6.38", "status": "unaffected", "versionType": "semver"}, {"version": "6.12.115", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver"}, {"version": "6.18.59", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver"}, {"version": "7.2.13", "lessThanOrEqual": "7.2.*", "status": "unaffected", "versionType": "semver"}, {"version": "7.3", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix"}]}], "cpeApplicability": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.38", "versionEndExcluding": "6.12.115"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.38", "versionEndExcluding": "6.18.59"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.38", "versionEndExcluding": "7.2.13"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.38", "versionEndExcluding": "7.3"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/fd60b32a99627fda479c9fa1d4a82fa9f7994670"}, {"url": "https://git.kernel.org/stable/c/b77e9622bbade9812e2090c66d25c372f515e921"}, {"url": "https://git.kernel.org/stable/c/f45ee1ff6358a22d7e22a4c53cb3148ea97b10d9"}, {"url": "https://git.kernel.org/stable/c/81d99abe2bd81379abfb595e403bbbee6fbfc624"}], "title": "x86/kvm: Don't consume async #PF flags on a kernel #PF in NMI context", "x_generator": {"engine": "bippy-1.2.0"}}}}

{}

{"affected": [{"affectedData": [{"defaultStatus": "unaffected", "product": "Linux", "programFiles": ["arch/x86/kernel/kvm.c"], "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "vendor": "Linux", "versions": [{"lessThan": "fd60b32a99627fda479c9fa1d4a82fa9f7994670", "status": "affected", "version": "631bc4878220932fe67fc46fc7cf7cccdb1ec597", "versionType": "git"}, {"lessThan": "b77e9622bbade9812e2090c66d25c372f515e921", "status": "affected", "version": "631bc4878220932fe67fc46fc7cf7cccdb1ec597", "versionType": "git"}, {"lessThan": "f45ee1ff6358a22d7e22a4c53cb3148ea97b10d9", "status": "affected", "version": "631bc4878220932fe67fc46fc7cf7cccdb1ec597", "versionType": "git"}, {"lessThan": "81d99abe2bd81379abfb595e403bbbee6fbfc624", "status": "affected", "version": "631bc4878220932fe67fc46fc7cf7cccdb1ec597", "versionType": "git"}]}, {"defaultStatus": "affected", "product": "Linux", "programFiles": ["arch/x86/kernel/kvm.c"], "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "vendor": "Linux", "versions": [{"status": "affected", "version": "2.6.38"}, {"lessThan": "2.6.38", "status": "unaffected", "version": "0", "versionType": "semver"}, {"lessThanOrEqual": "6.12.*", "status": "unaffected", "version": "6.12.115", "versionType": "semver"}, {"lessThanOrEqual": "6.18.*", "status": "unaffected", "version": "6.18.59", "versionType": "semver"}, {"lessThanOrEqual": "7.2.*", "status": "unaffected", "version": "7.2.13", "versionType": "semver"}, {"lessThanOrEqual": "*", "status": "unaffected", "version": "7.3", "versionType": "original_commit_for_fix"}]}], "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}], "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nx86/kvm: Don't consume async #PF flags on a kernel #PF in NMI context\n\nAn async #PF \"page not present\" event arrives through the #PF vector,\nand its reason sits in the per-CPU apf_reason.flags until\n__kvm_handle_async_pf() reads and clears it. If an NMI arrives after\nthe event is injected and before the #PF handler reads the flags, and\nthe NMI handler itself takes a #PF, that fault reads and clears the\nflags belonging to the #PF it interrupted. It then finds interrupts\ndisabled in the NMI context it interrupted, and panics:\n\n Kernel panic - not syncing: Host injected async #PF in interrupt\ndisabled region\n Call Trace:\n <NMI>\n panic+0x52/0x60\n __kvm_handle_async_pf+0xb0/0xb0\n exc_page_fault+0x71/0xb0\n asm_exc_page_fault+0x27/0x30\n RIP: 0010:__get_user_nocheck_8+0x6/0x20\n perf_callchain_user+0x147/0x1a0\n get_perf_callchain+0x12d/0x1c0\n ...\n perf_event_nmi_handler+0x26/0x50\n exc_nmi+0xe8/0x110\n RIP: 0010:asm_exc_page_fault+0x0/0x30\n </NMI>\n\nThe last RIP line shows the NMI landing on the first instruction of\nthe #PF entry. perf with user call chains takes such a fault: the\nsampling NMI walks the user stack with __get_user(), which faults when\na saved frame pointer is not a valid user address or the walk runs off\nthe top of the stack. The same window exists when KVM, running as an\nL1 hypervisor with DELIVERY_AS_PF_VMEXIT, reads the flags itself after\na #PF VM-exit.\n\nThe NMI entry code saves and restores CR2 for this nesting, but not the\nasync #PF reason. Andy Lutomirski described the race, with perf as the\nexample, when async #PF delivery was reworked in 2020 [1]. Saving and\nclearing the flags across the NMI, next to CR2, was discussed there but\nnot merged.\n\nSince that rework, Linux has stopped setting KVM_ASYNC_PF_SEND_ALWAYS,\nso the host delivers \"page not present\" only for user mode faults and\na kernel-mode fault in NMI context (including kernel-mode #MC and #DB)\ncannot be an async page fault. In that case, return without touching\nthe flags so that the interrupted handler finds them intact.\n\nTested on v7.3-rc5 in a 4-vCPU, 2 GiB guest restored from a snapshot\nwhose memory is served on demand through userfaultfd, so that reading\nit back takes async #PFs, while every thread samples hardware cycles\nwith user call chains and points its frame pointer at an unmapped page.\nWithout this patch the guest panicked as above in 3 of 3 runs. With it,\nthe guest survived 3 of 3 runs of 60 seconds, and the host counted\n148,441 to 153,334 kvm_async_pf_not_present events in the first 20\nseconds of each. On 6.18.50 the results were the same: the guest\npanicked without the patch and survived with it."}], "id": "CVE-2026-99178", "lastModified": "2026-11-01T13:18:02.150", "metrics": {}, "published": "2026-10-28T11:17:38.503", "references": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "url": "https://git.kernel.org/stable/c/81d99abe2bd81379abfb595e403bbbee6fbfc624"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "url": "https://git.kernel.org/stable/c/b77e9622bbade9812e2090c66d25c372f515e921"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "url": "https://git.kernel.org/stable/c/f45ee1ff6358a22d7e22a4c53cb3148ea97b10d9"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "url": "https://git.kernel.org/stable/c/fd60b32a99627fda479c9fa1d4a82fa9f7994670"}], "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "vulnStatus": "Received"}

{"bugzilla": {"description": "kernel: kernel: Denial of Service via race condition in KVM asynchronous page fault handling", "id": "2562721", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2562721"}, "csaw": false, "cvss3": {"cvss3_base_score": "4.7", "cvss3_scoring_vector": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H", "status": "draft"}, "cwe": "CWE-364", "details": ["In the Linux kernel, the following vulnerability has been resolved:\nx86/kvm: Don't consume async #PF flags on a kernel #PF in NMI context\nAn async #PF \"page not present\" event arrives through the #PF vector,\nand its reason sits in the per-CPU apf_reason.flags until\n__kvm_handle_async_pf() reads and clears it. If an NMI arrives after\nthe event is injected and before the #PF handler reads the flags, and\nthe NMI handler itself takes a #PF, that fault reads and clears the\nflags belonging to the #PF it interrupted. It then finds interrupts\ndisabled in the NMI context it interrupted, and panics:\nKernel panic - not syncing: Host injected async #PF in interrupt\ndisabled region\nCall Trace:\n<NMI>\npanic+0x52/0x60\n__kvm_handle_async_pf+0xb0/0xb0\nexc_page_fault+0x71/0xb0\nasm_exc_page_fault+0x27/0x30\nRIP: 0010:__get_user_nocheck_8+0x6/0x20\nperf_callchain_user+0x147/0x1a0\nget_perf_callchain+0x12d/0x1c0\n...\nperf_event_nmi_handler+0x26/0x50\nexc_nmi+0xe8/0x110\nRIP: 0010:asm_exc_page_fault+0x0/0x30\n</NMI>\nThe last RIP line shows the NMI landing on the first instruction of\nthe #PF entry. perf with user call chains takes such a fault: the\nsampling NMI walks the user stack with __get_user(), which faults when\na saved frame pointer is not a valid user address or the walk runs off\nthe top of the stack. The same window exists when KVM, running as an\nL1 hypervisor with DELIVERY_AS_PF_VMEXIT, reads the flags itself after\na #PF VM-exit.\nThe NMI entry code saves and restores CR2 for this nesting, but not the\nasync #PF reason. Andy Lutomirski described the race, with perf as the\nexample, when async #PF delivery was reworked in 2020 [1]. Saving and\nclearing the flags across the NMI, next to CR2, was discussed there but\nnot merged.\nSince that rework, Linux has stopped setting KVM_ASYNC_PF_SEND_ALWAYS,\nso the host delivers \"page not present\" only for user mode faults and\na kernel-mode fault in NMI context (including kernel-mode #MC and #DB)\ncannot be an async page fault. In that case, return without touching\nthe flags so that the interrupted handler finds them intact.\nTested on v7.3-rc5 in a 4-vCPU, 2 GiB guest restored from a snapshot\nwhose memory is served on demand through userfaultfd, so that reading\nit back takes async #PFs, while every thread samples hardware cycles\nwith user call chains and points its frame pointer at an unmapped page.\nWithout this patch the guest panicked as above in 3 of 3 runs. With it,\nthe guest survived 3 of 3 runs of 60 seconds, and the host counted\n148,441 to 153,334 kvm_async_pf_not_present events in the first 20\nseconds of each. On 6.18.50 the results were the same: the guest\npanicked without the patch and survived with it.", "A flaw was found in the Linux kernel's KVM (Kernel-based Virtual Machine) subsystem. When an asynchronous page fault is interrupted by a Non-Maskable Interrupt (NMI) that also encounters a page fault, the kernel improperly clears the pending fault status flags belonging to the interrupted handler. A local user can trigger this condition, causing the guest kernel to panic and resulting in a Denial of Service (DoS)."], "name": "CVE-2026-99178", "package_state": [{"cpe": "cpe:/o:redhat:enterprise_linux:10", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 10"}, {"cpe": "cpe:/o:redhat:enterprise_linux:6", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 6"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Not affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Not affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 9"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Not affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 9"}, {"cpe": "cpe:/a:redhat:openshift:4", "fix_state": "Not affected", "package_name": "openshift/ose-rhel-coreos-8", "product_name": "Red Hat OpenShift Container Platform 4"}, {"cpe": "cpe:/a:redhat:openshift:4", "fix_state": "Not affected", "package_name": "openshift/ose-rhel-coreos-9", "product_name": "Red Hat OpenShift Container Platform 4"}], "public_date": "2026-10-28T10:35:31Z", "references": ["https://www.cve.org/CVERecord?id=CVE-2026-99178\nhttps://nvd.nist.gov/vuln/detail/CVE-2026-99178\nhttps://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-99178.mbox"], "threat_severity": "Moderate"}