{"id":"CVE-2026-98637","kind":"vulnerability","aliases":["CVE-2026-98637"],"related":[],"title":"Linux KVM on arm64: SVE init failure leaves NULL state for guests","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: arm64: Do not clear VM-wide SVE feature on vCPU init failure\n\npkvm_vcpu_init_sve() clears KVM_ARM_VCPU_SVE in kvm->arch.vcpu_features\nwhen it fails, but vcpu_has_sve() tests KVM_ARCH_FLAG_GUEST_HAS_SVE,\nwhich is left set. Later vCPUs on that VM then skip the SVE setup and\nregister with a NULL sve_state, which the guest's first FP access hands\nto sve_load_state().\n\nReturn the error without touching vcpu_features.","summary":"When SVE setup fails for one vCPU in a pKVM arm64 guest, later vCPUs on the same VM skip SVE setup and are registered with a NULL SVE state. The guest's first floating-point access then passes that NULL pointer into sve_load_state(), which can crash the host kernel.","severity":"unknown","cvss":null,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["arm64","kvm","linux-kernel","pkvm","runtime"],"not_affected_if":[],"how_to_check":"- unknown","fix":"- Update the Linux kernel to a release containing the upstream commit that returns the error from pkvm_vcpu_init_sve() without clearing KVM_ARM_VCPU_SVE (version unknown from sources)","status":"open","published_at":"2026-10-18T16:17:16+00:00","first_seen_at":"2026-10-23T21:57:16+00:00","triaged_at":"2026-10-25T05:20:58+00:00","updated_at":"2026-10-25T05:20:58+00:00","category":"runtime","confidence":0.5,"triage":{"at":"2026-10-25T05:20:58Z","model":"claude-haiku-5-5","output":{"fix":"- Update the Linux kernel to a release containing the upstream commit that returns the error from pkvm_vcpu_init_sve() without clearing KVM_ARM_VCPU_SVE (version unknown from sources)","reach":"local","title":"Linux KVM on arm64: SVE init failure leaves NULL state for guests","impact":"medium","summary":"When SVE setup fails for one vCPU in a pKVM arm64 guest, later vCPUs on the same VM skip SVE setup and are registered with a NULL SVE state. The guest's first floating-point access then passes that NULL pointer into sve_load_state(), which can crash the host kernel.","category":"runtime","nicknames":[],"who_cares":["linux-kernel","kvm","arm64","pkvm"],"confidence":0.5,"needs_auth":"unknown","worst_case":"host kernel crash via NULL pointer dereference in guest SVE path","analyst_note":"Check the linked NVD entry and the upstream kernel stable commit for affected kernel version ranges and a CVSS score.","how_to_check":"- unknown","needs_analyst":true,"not_affected_if":[],"who_is_affected":"Hosts running the Linux kernel KVM hypervisor on arm64 with protected KVM (pKVM) and SVE-capable vCPUs are the relevant case. The sources do not say which configurations beyond that are affected, so treat the scope as unknown.","user_interaction":"no","needs_special_setup":"yes","severity_if_unknown":"unknown"},"cost_usd":0.000609,"input_tokens":3441,"output_tokens":529,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-2026':14A,17A '-98637':15A,18A 'access':62B,156C 'arch':124C 'arch.vcpu':113C 'arm':108C 'arm64':4A,19B,36B,89C 'clear':92C,106C 'crash':74B 'cve':13A,16A 'error':164C 'fail':29B,117C 'failur':7A,101C 'featur':97C,114C,168C 'first':58B,154C 'flag':125C 'float':60B 'floating-point':59B 'follow':83C 'fp':155C 'guest':12A,37B,56B,126C,152C 'hand':157C 'host':76B 'init':6A,100C,104C 'kernel':23B,77B,81C 'kvm':2A,20B,88C,107C,112C,123C 'later':38B,133C 'leav':8A 'left':131C 'linux':1A,22B,80C 'linux-kernel':21B 'load':70B,160C 'null':9A,52B,66B,147C 'one':31B 'pass':64B 'pkvm':24B,35B,102C 'point':61B 'pointer':67B 'regist':49B,144C 'resolv':87C 'return':162C 'runtim':25B 'set':132C 'setup':28B,46B,142C 'skip':44B,139C 'state':10A,54B,71B,149C,161C 'sve':5A,27B,45B,53B,69B,96C,105C,110C,121C,128C,141C,148C,159C 'test':122C 'touch':166C 'vcpu':32B,99C,103C,109C,119C,167C 'vcpus':39B,134C 'vm':43B,94C,137C 'vm-wide':93C 'vulner':84C 'wide':95C 'without':165C","nicknames":[],"mitigations":[],"who_affected":"Hosts running the Linux kernel KVM hypervisor on arm64 with protected KVM (pKVM) and SVE-capable vCPUs are the relevant case. The sources do not say which configurations beyond that are affected, so treat the scope as unknown.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-18T16:17:16+00:00","kev":null,"cvss_vector":null,"cvss_by":null,"poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-98637","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-98637","severity":null,"published_at":"2026-10-18T16:17:16+00:00","modified_at":"2026-10-19T10:19:27+00:00","first_seen_at":"2026-10-23T21:57:16+00:00","fetched_at":"2026-10-23T22:28:56+00:00","note":null}],"documents":[],"notice":"Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai"}