{"id":"CVE-2026-98683","kind":"vulnerability","aliases":["CVE-2026-98683"],"related":[],"title":"Linux kernel SMB client: interior zero-range can refill with stale data","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: flush dirty data before zeroing a range\n\nsmb3_zero_range() emulates FALLOC_FL_ZERO_RANGE by invalidating the\npage cache over the target range with truncate_pagecache_range() and\nthen issuing FSCTL_SET_ZERO_DATA to the server.\n\nDirty data was only flushed conditionally, when the range reached or\nextended EOF.  For a purely interior zero range that does not reach\nEOF, no flush happened, so a dirty folio overlapping the range could\nbe written back to the server after the FSCTL and refill the range\nthat was just zeroed with stale data.\n\nFix this by unconditionally flushing and waiting for dirty data in the\nrange before invalidating the page cache and issuing\nFSCTL_SET_ZERO_DATA, exactly as was done for smb3_punch_hole() in\ncommit d7d2adcd022b (\"smb/client: flush dirty data before punching a\nhole\"); the two paths are structurally identical here.\n\nThis is observed as generic/363 randomly reading stale data where a\nzeroed range is expected against Windows Server.","summary":"In the Linux kernel's SMB3 client, a zero-range operation over an interior part of a file did not flush dirty page-cache data first, so a dirty page could be written back after the server zeroed the range and restore old contents. The fix flushes and waits for dirty data in the range before invalidating the cache and issuing the zero-data request.","severity":"unknown","cvss":null,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["cifs","kernel","linux","runtime","smb3","windows-server"],"not_affected_if":["no-smb-mounts","no-zero-range-fallocate"],"how_to_check":"- `uname -r` and compare against the kernel version that contains the upstream fix (unknown from the sources)\n- Check whether the kernel includes commit d7d2adcd022b's sibling change for smb3_zero_range (unknown from the sources)\n- Mounts using SMB3 with `mount -t cifs` or `mount -t smb3` on the affected host","fix":"- Update the Linux kernel to a release that includes the upstream fix for smb3_zero_range (fixed version unknown from the sources)\n- Until patched, avoid fallocate zero-range on SMB3 mounts where data integrity matters (unknown from the sources)","status":"open","published_at":"2026-10-18T16:17:21+00:00","first_seen_at":"2026-10-23T21:57:16+00:00","triaged_at":"2026-10-25T05:19:12+00:00","updated_at":"2026-10-25T05:19:12+00:00","category":"runtime","confidence":0.5,"triage":{"at":"2026-10-25T05:19:12Z","model":"claude-haiku-5-5","output":{"fix":"- Update the Linux kernel to a release that includes the upstream fix for smb3_zero_range (fixed version unknown from the sources)\n- Until patched, avoid fallocate zero-range on SMB3 mounts where data integrity matters (unknown from the sources)","reach":"network","title":"Linux kernel SMB client: interior zero-range can refill with stale data","impact":"low","summary":"In the Linux kernel's SMB3 client, a zero-range operation over an interior part of a file did not flush dirty page-cache data first, so a dirty page could be written back after the server zeroed the range and restore old contents. The fix flushes and waits for dirty data in the range before invalidating the cache and issuing the zero-data request.","category":"runtime","nicknames":[],"who_cares":["linux","kernel","smb3","cifs","windows-server"],"confidence":0.5,"needs_auth":"unknown","worst_case":"stale file data reappears in ranges expected to be zeroed","analyst_note":"Find the fixed kernel versions and the stable backport commit for the smb3_zero_range flush fix in the NVD or kernel.org stable entries.","how_to_check":"- `uname -r` and compare against the kernel version that contains the upstream fix (unknown from the sources)\n- Check whether the kernel includes commit d7d2adcd022b's sibling change for smb3_zero_range (unknown from the sources)\n- Mounts using SMB3 with `mount -t cifs` or `mount -t smb3` on the affected host","needs_analyst":true,"not_affected_if":["no-smb-mounts","no-zero-range-fallocate"],"who_is_affected":"Systems running a Linux kernel with the SMB3 client (cifs/smb3) that mount network shares and use fallocate FALLOC_FL_ZERO_RANGE on files over SMB. The sources observed stale reads against Windows Server in the generic/363 test. Hosts that do not mount SMB shares, or that do not use zero-range fallocate, can skip it.","user_interaction":"unknown","needs_special_setup":"unknown","severity_if_unknown":"unknown"},"cost_usd":0.000726,"input_tokens":3598,"output_tokens":733,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-2026':15A,18A '-98683':16A,19A 'back':63B,183C 'cach':53B,88B,127C,218C 'cif':20B 'client':4A,34B,107C 'commit':234C 'condit':151C 'content':73B 'could':60B,180C 'cve':14A,17A 'd7d2adcd022b':235C 'data':13A,54B,81B,94B,110C,142C,147C,200C,210C,224C,239C,259C 'dirti':50B,58B,80B,109C,146C,175C,209C,238C 'done':228C 'emul':118C 'eof':158C,169C 'exact':225C 'expect':265C 'extend':157C 'falloc':119C 'file':46B 'first':55B 'fix':75B,201C 'fl':120C 'flush':49B,76B,108C,150C,171C,205C,237C 'folio':176C 'follow':101C 'fsctl':139C,189C,221C 'generic/363':255C 'happen':172C 'hole':232C,243C 'ident':249C 'interior':5A,42B,162C 'invalid':86B,124C,215C 'issu':90B,138C,220C 'kernel':2A,21B,31B,99C 'linux':1A,22B,30B,98C 'observ':253C 'old':72B 'oper':39B 'overlap':177C 'page':52B,59B,126C,217C 'page-cach':51B 'pagecach':134C 'part':43B 'path':246C 'punch':231C,241C 'pure':161C 'random':256C 'rang':8A,38B,69B,84B,114C,117C,122C,131C,135C,154C,164C,179C,193C,213C,263C 'reach':155C,168C 'read':257C 'refil':10A,191C 'request':95B 'resolv':105C 'restor':71B 'runtim':23B 'server':27B,66B,145C,186C,268C 'set':140C,222C 'smb':3A,106C 'smb/client':236C 'smb3':24B,33B,115C,230C 'stale':12A,199C,258C 'structur':248C 'target':130C 'truncat':133C 'two':245C 'uncondit':204C 'vulner':102C 'wait':78B,207C 'window':26B,267C 'windows-serv':25B 'written':62B,182C 'zero':7A,37B,67B,93B,112C,116C,121C,141C,163C,197C,223C,262C 'zero-data':92B 'zero-rang':6A,36B","nicknames":[],"mitigations":[],"who_affected":"Systems running a Linux kernel with the SMB3 client (cifs/smb3) that mount network shares and use fallocate FALLOC_FL_ZERO_RANGE on files over SMB. The sources observed stale reads against Windows Server in the generic/363 test. Hosts that do not mount SMB shares, or that do not use zero-range fallocate, can skip it.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-18T16:17:21+00:00","kev":null,"cvss_vector":null,"cvss_by":null,"poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-98683","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-98683","severity":null,"published_at":"2026-10-18T16:17:21+00:00","modified_at":"2026-10-19T10:19:32+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"}