{"id":"CVE-2026-99137","kind":"vulnerability","aliases":["CVE-2026-99137"],"related":[],"title":"Linux kernel CIFS: truncate can leave a wrong file size on failed open","description":"In the Linux kernel, the following vulnerability has been resolved:\n\ncifs: don't update i_size in cifs_do_truncate without a cached handle\n\nIf find_writable_file() returns null, cifs_file_flush will return\n0 without issuing set_file_size, and the outer 'if (!rc)' block\nwill set i_size to 0 before telling the server to truncate.  If\nthe cifs_open() then fails, the inode will have size 0, while\nthe server file is unchanged.\n\nMove the netfs_resize_file() and cifs_setsize() into the 'if\n(cfile)', so they only run after a successful set_file_size.\n\nIn the no-handle else branch, evict stale pages with\ntruncate_inode_pages before the O_TRUNC open to dispose of old\ncache pages, and let the open response set the i_size.","summary":"In the Linux kernel's CIFS client, a truncate with no cached file handle could set the local inode size to 0 even when the server-side truncate never happened. The mismatch between local and server file size is the reported flaw; the sources do not describe an attacker gaining code execution or data access.","severity":"unknown","cvss":null,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["cifs","linux-kernel","runtime","smb"],"not_affected_if":["no-cifs-mounts"],"how_to_check":"- unknown","fix":"- unknown","status":"open","published_at":"2026-10-28T11:17:33+00:00","first_seen_at":"2026-10-28T11:32:35+00:00","triaged_at":"2026-10-28T11:36:10+00:00","updated_at":"2026-10-28T11:36:10+00:00","category":"runtime","confidence":0.5,"triage":{"at":"2026-10-28T11:36:10Z","model":"claude-haiku-5-5","output":{"fix":"- unknown","reach":"unknown","title":"Linux kernel CIFS: truncate can leave a wrong file size on failed open","impact":"low","summary":"In the Linux kernel's CIFS client, a truncate with no cached file handle could set the local inode size to 0 even when the server-side truncate never happened. The mismatch between local and server file size is the reported flaw; the sources do not describe an attacker gaining code execution or data access.","category":"runtime","nicknames":[],"who_cares":["linux-kernel","cifs","smb"],"confidence":0.5,"needs_auth":"unknown","worst_case":"local file size metadata becomes inconsistent with server copy","analyst_note":"Find the NVD entry's affected kernel version ranges and the upstream fix commit to fill in the fix and check fields.","how_to_check":"- unknown","needs_analyst":true,"not_affected_if":["no-cifs-mounts"],"who_is_affected":"Systems running a Linux kernel that includes the CIFS/SMB client and mount SMB shares for file access. The sources do not give affected kernel versions or say whether systems without CIFS mounts are exposed.","user_interaction":"unknown","needs_special_setup":"unknown","severity_if_unknown":"unknown"},"cost_usd":0.000567,"input_tokens":3477,"output_tokens":439,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-2026':15A,18A '-99137':16A,19A '0':47B,117C,134C,152C 'access':81B 'attack':75B 'block':128C 'branch':187C 'cach':37B,104C,204C 'cfile':170C 'cif':3A,20B,31B,92C,99C,112C,143C,165C 'client':32B 'code':77B 'could':40B 'cve':14A,17A 'data':80B 'describ':73B 'dispos':201C 'els':186C 'even':48B 'evict':188C 'execut':78B 'fail':12A,146C 'file':9A,38B,63B,109C,113C,121C,156C,163C,179C 'find':107C 'flaw':68B 'flush':114C 'follow':87C 'gain':76B 'handl':39B,105C,185C 'happen':56B 'inod':44B,148C,193C 'issu':119C 'kernel':2A,23B,29B,85C 'leav':6A 'let':207C 'linux':1A,22B,28B,84C 'linux-kernel':21B 'local':43B,60B 'mismatch':58B 'move':159C 'netf':161C 'never':55B 'no-handl':183C 'null':111C 'o':197C 'old':203C 'open':13A,144C,199C,209C 'outer':125C 'page':190C,194C,205C 'rc':127C 'report':67B 'resiz':162C 'resolv':91C 'respons':210C 'return':110C,116C 'run':174C 'runtim':24B 'server':52B,62B,138C,155C 'server-sid':51B 'set':41B,120C,130C,178C,211C 'setsiz':166C 'side':53B 'size':10A,45B,64B,97C,122C,132C,151C,180C,214C 'smb':25B 'sourc':70B 'stale':189C 'success':177C 'tell':136C 'trunc':198C 'truncat':4A,34B,54B,101C,140C,192C 'unchang':158C 'updat':95C 'vulner':88C 'without':102C,118C 'writabl':108C 'wrong':8A","nicknames":[],"mitigations":[],"who_affected":"Systems running a Linux kernel that includes the CIFS/SMB client and mount SMB shares for file access. The sources do not give affected kernel versions or say whether systems without CIFS mounts are exposed.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-28T11:17:33+00:00","kev":null,"cvss_vector":null,"cvss_by":null,"poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-99137","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-99137","severity":null,"published_at":"2026-10-28T11:17:33+00:00","modified_at":"2026-10-28T11:17:33+00:00","first_seen_at":"2026-10-28T11:32:35+00:00","fetched_at":"2026-10-28T11:32:35+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"}