{"id":"CVE-2026-99063","kind":"vulnerability","aliases":["CVE-2026-99063"],"related":[],"title":"Linux kernel: device-mapper ioctl over-reads a buffer, leaking adjacent kernel memory","description":"In the Linux kernel, the following vulnerability has been resolved:\n\ndm ioctl: don't let data_start run past the buffer\n\nstruct dm_ioctl has seven bytes of trailing padding, so the smallest\nbuffer userspace is allowed to ask for, offsetof(struct dm_ioctl, data),\nis seven bytes shorter than sizeof(struct dm_ioctl).\n\nget_result_buffer() sets data_start to sizeof(struct dm_ioctl) without\nlooking at how big the buffer actually is. Ask for the minimum and\ndata_start ends up seven bytes past the end. Callers add it to\ndata_size, and ctl_ioctl() copies that much back to userspace:\n\n  BUG: KASAN: slab-out-of-bounds in _copy_to_user+0xad/0xd0\n  Read of size 312 at addr ffff8880169e4c00 by task repro-dm/140\n   ctl_ioctl+0x5e3/0xcb0\n   dm_ctl_ioctl+0x25/0x40\n  allocated 305-byte region [ffff8880169e4c00, ffff8880169e4d31)\n\nA DM_LIST_DEVICES with data_size set to 305 is enough to hit it, and the\nseven bytes that leak are whatever sat next to the allocation.\n\nClamp data_start to the buffer size.\n\nNote that this is not a security bug because the out-of-bounds read can\nonly be triggered by root.","summary":"The device-mapper ioctl handler sets its data offset past a small caller-supplied buffer, so copying the result back to userspace reads seven bytes beyond the allocation. The sources say only root can trigger it, and that the leaked bytes are whatever sat next to the allocation.","severity":"low","cvss":null,"epss":0.00209,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["device-mapper","kernel","linux","runtime","self-hosted"],"not_affected_if":["managed-hosting","no-untrusted-root"],"how_to_check":null,"fix":null,"status":"open","published_at":"2026-10-23T13:17:30+00:00","first_seen_at":"2026-10-23T21:57:34+00:00","triaged_at":"2026-10-25T04:53:52+00:00","updated_at":"2026-10-25T12:38:50+00:00","category":"runtime","confidence":0.6,"triage":{"at":"2026-10-25T04:53:52Z","model":"claude-haiku-5-5","output":{"fix":"unknown","reach":"local","title":"Linux kernel: device-mapper ioctl over-reads a buffer, leaking adjacent kernel memory","impact":"low","summary":"The device-mapper ioctl handler sets its data offset past a small caller-supplied buffer, so copying the result back to userspace reads seven bytes beyond the allocation. The sources say only root can trigger it, and that the leaked bytes are whatever sat next to the allocation.","category":"runtime","nicknames":[],"who_cares":["linux","kernel","device-mapper","self-hosted"],"confidence":0.6,"needs_auth":"yes","worst_case":"root-only read of seven bytes of adjacent kernel memory","analyst_note":"Find the kernel release that carries the dm ioctl fix and the affected version range; the sources give neither.","how_to_check":"unknown","needs_analyst":true,"not_affected_if":["no-untrusted-root","managed-hosting"],"who_is_affected":"Only systems where a local user can already run device-mapper ioctls as root, which the sources say is the only way to trigger the over-read. Systems where no untrusted local account has root access are not exposed in practice. The sources do not name affected kernel versions.","user_interaction":"no","needs_special_setup":"unknown","severity_if_unknown":"low"},"cost_usd":0.000597,"input_tokens":3689,"output_tokens":457,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'+0':195C,212C,217C '-2026':17A,20A '-99063':18A,21A '/140':209C '305':220C,234C '312':200C 'actual':153C 'add':170C 'addr':202C 'adjac':13A 'alloc':60B,80B,219C,252C 'allow':117C 'ask':119C,155C 'back':52B,181C 'beyond':58B 'big':150C 'bound':190C,273C 'buffer':11A,47B,101C,114C,137C,152C,258C 'bug':184C,267C 'byte':57B,73B,107C,128C,165C,221C,243C 'caller':45B,169C 'caller-suppli':44B 'clamp':253C 'copi':49B,178C,192C 'ctl':176C,210C,215C 'cve':16A,19A 'data':39B,96C,125C,139C,160C,173C,230C,254C 'devic':4A,23B,33B,228C 'device-mapp':3A,22B,32B 'dm':91C,103C,123C,133C,144C,208C,214C,226C 'end':162C,168C 'enough':236C 'ffff8880169e4c00':203C,223C 'ffff8880169e4d31':224C 'follow':86C 'get':135C 'handler':36B 'hit':238C 'host':30B 'ioctl':6A,35B,92C,104C,124C,134C,145C,177C,211C,216C 'kasan':185C 'kernel':2A,14A,25B,84C 'leak':12A,72B,245C 'let':95C 'linux':1A,26B,83C 'list':227C 'look':147C 'mapper':5A,24B,34B 'memori':15A 'minimum':158C 'much':180C 'next':77B,249C 'note':260C 'offset':40B 'offsetof':121C 'out-of-bound':270C 'over-read':7A 'pad':110C 'past':41B,99C,166C 'read':9A,55B,197C,274C 'region':222C 'repro':207C 'repro-dm':206C 'resolv':90C 'result':51B,136C 'root':65B,280C 'run':98C 'runtim':27B 'sat':76B,248C 'say':63B 'secur':266C 'self':29B 'self-host':28B 'set':37B,138C,232C 'seven':56B,106C,127C,164C,242C 'shorter':129C 'size':174C,199C,231C,259C 'sizeof':131C,142C 'slab':187C 'slab-out-of-bound':186C 'small':43B 'smallest':113C 'sourc':62B 'start':97C,140C,161C,255C 'struct':102C,122C,132C,143C 'suppli':46B 'task':205C 'trail':109C 'trigger':67B,278C 'user':194C 'userspac':54B,115C,183C 'vulner':87C 'whatev':75B,247C 'without':146C 'x25/0x40':218C 'x5e3/0xcb0':213C 'xad/0xd0':196C","nicknames":[],"mitigations":[],"who_affected":"Only systems where a local user can already run device-mapper ioctls as root, which the sources say is the only way to trigger the over-read. Systems where no untrusted local account has root access are not exposed in practice. The sources do not name affected kernel versions.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-23T13:17:30+00:00","kev":null,"cvss_vector":null,"cvss_by":null,"poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-99063","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-99063","severity":null,"published_at":"2026-10-23T13:17:30+00:00","modified_at":"2026-10-23T13:17:30+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-2026-99063","url":"https://api.first.org/data/v1/epss?cve=CVE-2026-99063","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"}