{"id":"CVE-2026-98653","kind":"vulnerability","aliases":["CVE-2026-98653"],"related":[],"title":"Linux KVM on s390: nested guest shadow fault returns wrong error","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: s390: Fix _gaccess_shadow_fault()\n\nIn some circumstances, it is possible that the page of nested guest\nmemory that is being shadowed is not present at all in the parent guest\ngmap. dat_entry_walk() will not find any leaf entry and return with\n-ENOENT, which will erroneously be propagated all the way to userspace.\n\nFix by manually calling gmap_link() on the memory of the nested guest\nthat is being shadowed if the mapping was not already present.","summary":"In the Linux kernel's KVM for IBM s390, a nested guest's memory page that is missing from the parent guest mapping is reported as an error and propagated to userspace instead of being mapped. The sources describe this as a correctness bug fixed by linking the missing mapping, and do not state an attacker gain.","severity":"unknown","cvss":null,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["infrastructure","kvm","linux-kernel","s390","self-hosted"],"not_affected_if":["no-nested-guests","non-s390-architecture"],"how_to_check":"- Run `uname -r` on s390 hosts to see the kernel version, then compare against the fixed kernel release in the upstream commit.\n- Check whether the host runs KVM nested virtualization on s390 (unknown from the sources).","fix":"- Update the Linux kernel to a release that includes the upstream fix for _gaccess_shadow_fault() (the exact version is unknown from the sources).","status":"open","published_at":"2026-10-18T16:17:18+00:00","first_seen_at":"2026-10-23T21:57:16+00:00","triaged_at":"2026-10-25T05:19:37+00:00","updated_at":"2026-10-25T05:19:37+00:00","category":"infrastructure","confidence":0.4,"triage":{"at":"2026-10-25T05:19:37Z","model":"claude-haiku-5-5","output":{"fix":"- Update the Linux kernel to a release that includes the upstream fix for _gaccess_shadow_fault() (the exact version is unknown from the sources).","reach":"unknown","title":"Linux KVM on s390: nested guest shadow fault returns wrong error","impact":"low","summary":"In the Linux kernel's KVM for IBM s390, a nested guest's memory page that is missing from the parent guest mapping is reported as an error and propagated to userspace instead of being mapped. The sources describe this as a correctness bug fixed by linking the missing mapping, and do not state an attacker gain.","category":"infrastructure","nicknames":[],"who_cares":["linux-kernel","kvm","s390","self-hosted"],"confidence":0.4,"needs_auth":"unknown","worst_case":"unknown; the sources describe a wrong error return to userspace","analyst_note":"Check the NVD entry and the upstream kernel commit for the affected version range and any security impact beyond the error propagation.","how_to_check":"- Run `uname -r` on s390 hosts to see the kernel version, then compare against the fixed kernel release in the upstream commit.\n- Check whether the host runs KVM nested virtualization on s390 (unknown from the sources).","needs_analyst":true,"not_affected_if":["non-s390-architecture","no-nested-guests"],"who_is_affected":"Only hosts running the Linux kernel KVM module on IBM s390 hardware with nested guests are plausibly affected. Hosts on other architectures, or without nested KVM guests on s390, can likely skip it; the sources do not say more.","user_interaction":"no","needs_special_setup":"yes","severity_if_unknown":"unknown"},"cost_usd":0.000634,"input_tokens":3402,"output_tokens":588,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-2026':13A,16A '-98653':14A,17A 'alreadi':172C 'attack':82B 'bug':70B 'call':153C 'circumst':102C 'correct':69B 'cve':12A,15A 'dat':127C 'describ':65B 'enoent':139C 'entri':128C,135C 'erron':142C 'error':11A,54B 'fault':8A,99C 'find':132C 'fix':71B,96C,150C 'follow':89C 'gaccess':97C 'gain':83B 'gmap':126C,154C 'guest':6A,38B,48B,111C,125C,162C 'host':26B 'ibm':34B 'infrastructur':18B 'instead':59B 'kernel':22B,30B,87C 'kvm':2A,19B,32B,94C 'leaf':134C 'link':73B,155C 'linux':1A,21B,29B,86C 'linux-kernel':20B 'manual':152C 'map':49B,62B,76B,169C 'memori':40B,112C,158C 'miss':44B,75B 'nest':5A,37B,110C,161C 'page':41B,108C 'parent':47B,124C 'possibl':105C 'present':119C,173C 'propag':56B,144C 'report':51B 'resolv':93C 'return':9A,137C 's390':4A,23B,35B,95C 'self':25B 'self-host':24B 'shadow':7A,98C,116C,166C 'sourc':64B 'state':80B 'userspac':58B,149C 'vulner':90C 'walk':129C 'way':147C 'wrong':10A","nicknames":[],"mitigations":[],"who_affected":"Only hosts running the Linux kernel KVM module on IBM s390 hardware with nested guests are plausibly affected. Hosts on other architectures, or without nested KVM guests on s390, can likely skip it; the sources do not say more.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-18T16:17:18+00:00","kev":null,"cvss_vector":null,"cvss_by":null,"poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-98653","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-98653","severity":null,"published_at":"2026-10-18T16:17:18+00:00","modified_at":"2026-10-19T10:19:29+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"}