{"id":"CVE-2026-98585","kind":"vulnerability","aliases":["CVE-2026-98585"],"related":[],"title":"Linux kernel fbnic driver: zero ring size handling in ethtool","description":"In the Linux kernel, the following vulnerability has been resolved:\n\neth: fbnic: Avoid rounding zero ring sizes\n\nroundup_pow_of_two() is undefined for zero. ethtool permits a zero ring\nsize to reach the driver, where the minimum-size check should reject it.\n\nLeave zero unchanged while rounding nonzero ring sizes. The minimum-size\ncheck then rejects zero deterministically without changing the established\nbehavior for other values.","summary":"A Linux kernel driver for Meta's fbnic network hardware passed zero ring sizes through ethtool to a rounding function that is undefined for zero. The fix leaves zero unchanged so the existing minimum-size check rejects it.","severity":"unknown","cvss":null,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["fbnic","infrastructure","linux-kernel","network-driver"],"not_affected_if":["no-fbnic-hardware"],"how_to_check":"- unknown","fix":"- Update to a Linux kernel release that includes the fbnic ring size fix (the sources do not name the version).","status":"open","published_at":"2026-10-18T16:17:11+00:00","first_seen_at":"2026-10-23T21:57:15+00:00","triaged_at":"2026-10-25T05:22:57+00:00","updated_at":"2026-10-25T05:22:57+00:00","category":"infrastructure","confidence":0.4,"triage":{"at":"2026-10-25T05:22:57Z","model":"claude-haiku-5-5","output":{"fix":"- Update to a Linux kernel release that includes the fbnic ring size fix (the sources do not name the version).","reach":"local","title":"Linux kernel fbnic driver: zero ring size handling in ethtool","impact":"low","summary":"A Linux kernel driver for Meta's fbnic network hardware passed zero ring sizes through ethtool to a rounding function that is undefined for zero. The fix leaves zero unchanged so the existing minimum-size check rejects it.","category":"infrastructure","nicknames":[],"who_cares":["linux-kernel","fbnic","network-driver"],"confidence":0.4,"needs_auth":"unknown","worst_case":"unknown; the sources describe undefined behavior from a zero ring size","analyst_note":"Check the NVD entry and the upstream kernel commit for the fixed kernel versions and the actual impact of the undefined behavior.","how_to_check":"- unknown","needs_analyst":true,"not_affected_if":["no-fbnic-hardware"],"who_is_affected":"Systems running the Linux kernel with the fbnic network driver loaded, which is only present on hosts with that Meta fbnic NIC hardware. The sources do not say what an attacker would need to trigger the flaw, and the impact is not described beyond undefined behavior. Hosts without fbnic hardware can skip it.","user_interaction":"unknown","needs_special_setup":"unknown","severity_if_unknown":"low"},"cost_usd":0.000588,"input_tokens":3370,"output_tokens":502,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-2026':12A,15A '-98585':13A,16A 'avoid':75C 'behavior':128C 'chang':125C 'check':61B,103C,119C 'cve':11A,14A 'determinist':123C 'driver':4A,24B,28B,97C 'establish':127C 'eth':73C 'ethtool':10A,40B,88C 'exist':57B 'fbnic':3A,17B,32B,74C 'fix':51B 'follow':68C 'function':44B 'handl':8A 'hardwar':34B 'infrastructur':18B 'kernel':2A,21B,27B,66C 'leav':52B,107C 'linux':1A,20B,26B,65C 'linux-kernel':19B 'meta':30B 'minimum':59B,101C,117C 'minimum-s':58B,100C,116C 'network':23B,33B 'network-driv':22B 'nonzero':112C 'pass':35B 'permit':89C 'pow':81C 'reach':95C 'reject':62B,105C,121C 'resolv':72C 'ring':6A,37B,78C,92C,113C 'round':43B,76C,111C 'roundup':80C 'size':7A,38B,60B,79C,93C,102C,114C,118C 'two':83C 'unchang':54B,109C 'undefin':47B,85C 'valu':131C 'vulner':69C 'without':124C 'zero':5A,36B,49B,53B,77C,87C,91C,108C,122C","nicknames":[],"mitigations":[],"who_affected":"Systems running the Linux kernel with the fbnic network driver loaded, which is only present on hosts with that Meta fbnic NIC hardware. The sources do not say what an attacker would need to trigger the flaw, and the impact is not described beyond undefined behavior. Hosts without fbnic hardware can skip it.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-18T16:17:11+00:00","kev":null,"cvss_vector":null,"cvss_by":null,"poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-98585","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-98585","severity":null,"published_at":"2026-10-18T16:17:11+00:00","modified_at":"2026-10-19T10:19:19+00:00","first_seen_at":"2026-10-23T21:57:15+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"}