{"id":"CVE-2026-99071","kind":"vulnerability","aliases":["CVE-2026-99071"],"related":[],"title":"Linux kernel: IPv4 route notification size race triggers spurious kernel warning","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nipv4: do not warn on route notification size race\n\nCommit 680aea08e78c (\"net: ipv4: Emit notification when fib hardware\nflags are changed\") added asynchronous route notifications for hardware\nflag changes.\n\nfib_alias_hw_flags_set() sizes the skb with fib_nlmsg_size() and later\nfills it with fib_dump_info() while holding only RCU.  With nexthop\ncompatibility mode enabled, a concurrent replacement can grow the group\nbetween these independent snapshots.  fib_dump_info() can then\nlegitimately return -EMSGSIZE, so the warning does not prove a sizing bug.\n\nRemove the warning.  The existing error path still frees the skb and\nreports the error to listeners.","summary":"When hardware flags on an IPv4 route change while nexthop groups are being replaced, the kernel can build a route notification that is too small and then hit a warning path. The fix removes that warning; the error path that frees the buffer and reports the failure is unchanged.","severity":"unknown","cvss":null,"epss":0.00209,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["ipv4-routing","linux-kernel","nexthop-groups","runtime"],"not_affected_if":["default-config"],"how_to_check":"- unknown","fix":"- unknown","status":"open","published_at":"2026-10-23T13:17:31+00:00","first_seen_at":"2026-10-23T21:57:34+00:00","triaged_at":"2026-10-25T04:53:46+00:00","updated_at":"2026-10-25T12:38:50+00:00","category":"runtime","confidence":0.5,"triage":{"at":"2026-10-25T04:53:46Z","model":"claude-haiku-5-5","output":{"fix":"- unknown","reach":"local","title":"Linux kernel: IPv4 route notification size race triggers spurious kernel warning","impact":"low","summary":"When hardware flags on an IPv4 route change while nexthop groups are being replaced, the kernel can build a route notification that is too small and then hit a warning path. The fix removes that warning; the error path that frees the buffer and reports the failure is unchanged.","category":"runtime","nicknames":[],"who_cares":["linux-kernel","ipv4-routing","nexthop-groups"],"confidence":0.5,"needs_auth":"unknown","worst_case":"Kernel log warning fires; no clear code execution or data exposure stated.","analyst_note":"Check the upstream kernel commit 680aea08e78c and the fixing commit for affected and fixed kernel versions, and confirm there is no security impact beyond the warning.","how_to_check":"- unknown","needs_analyst":true,"not_affected_if":["default-config"],"who_is_affected":"Systems running a Linux kernel with IPv4 routing and nexthop compatibility mode enabled, where routes are offloaded to hardware and replaced concurrently. The sources do not say which kernel versions are affected or whether the warning has any security consequence beyond log noise.","user_interaction":"no","needs_special_setup":"yes","severity_if_unknown":"unknown"},"cost_usd":0.000585,"input_tokens":3475,"output_tokens":474,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-2026':13A,16A '-99071':14A,17A '680aea08e78c':97C 'add':108C 'alia':117C 'asynchron':109C 'buffer':70B 'bug':172C 'build':45B 'chang':35B,107C,115C 'commit':96C 'compat':142C 'concurr':146C 'cve':12A,15A 'dump':134C,157C 'emit':100C 'emsgsiz':163C 'enabl':144C 'error':65B,178C,187C 'exist':177C 'failur':74B 'fib':103C,116C,125C,133C,156C 'fill':130C 'fix':60B 'flag':30B,105C,114C,119C 'follow':82C 'free':68B,181C 'group':26B,38B,151C 'grow':149C 'hardwar':29B,104C,113C 'hit':55B 'hold':137C 'hw':118C 'independ':154C 'info':135C,158C 'ipv4':3A,19B,33B,87C,99C 'ipv4-routing':18B 'kernel':2A,10A,23B,43B,80C 'later':129C 'legitim':161C 'linux':1A,22B,79C 'linux-kernel':21B 'listen':189C 'mode':143C 'net':98C 'nexthop':25B,37B,141C 'nexthop-group':24B 'nlmsg':126C 'notif':5A,48B,93C,101C,111C 'path':58B,66B,179C 'prove':169C 'race':7A,95C 'rcu':139C 'remov':61B,173C 'replac':41B,147C 'report':72B,185C 'resolv':86C 'return':162C 'rout':4A,20B,34B,47B,92C,110C 'runtim':27B 'set':120C 'size':6A,94C,121C,127C,171C 'skb':123C,183C 'small':52B 'snapshot':155C 'spurious':9A 'still':180C 'trigger':8A 'unchang':76B 'vulner':83C 'warn':11A,57B,63B,90C,166C,175C","nicknames":[],"mitigations":[],"who_affected":"Systems running a Linux kernel with IPv4 routing and nexthop compatibility mode enabled, where routes are offloaded to hardware and replaced concurrently. The sources do not say which kernel versions are affected or whether the warning has any security consequence beyond log noise.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-23T13:17:31+00:00","kev":null,"cvss_vector":null,"cvss_by":null,"poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-99071","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-99071","severity":null,"published_at":"2026-10-23T13:17:31+00:00","modified_at":"2026-10-23T13:17:31+00:00","first_seen_at":"2026-10-23T21:57:34+00:00","fetched_at":"2026-10-23T22:29:03+00:00","note":null},{"source":"epss","external_id":"CVE-2026-99071","url":"https://api.first.org/data/v1/epss?cve=CVE-2026-99071","severity":null,"published_at":null,"modified_at":null,"first_seen_at":"2026-10-25T12:38:50+00:00","fetched_at":"2026-10-25T12:38:50+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"}