{"id":"CVE-2026-99052","kind":"vulnerability","aliases":["CVE-2026-99052"],"related":[],"title":"Linux kernel SELinux: second NFSv4 mount silently disables per-file labeling","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nselinux: preserve NATIVE_LABELS on already-initialized sb in set_mnt_opts\n\nWhen an NFSv4 filesystem exported with security_label is mounted a\nsecond time, sget_fc() returns the existing superblock and\nnfs_get_root() calls security_sb_set_mnt_opts() again on it. Since the\nsuperblock is already SB_INITIALIZED, selinux_set_mnt_opts() takes an\nearly exit without setting SECURITY_LSM_NATIVE_LABELS in\n*set_kern_flags. nfs_get_root() then sees kflags without\nSECURITY_LSM_NATIVE_LABELS set and clears NFS_CAP_SECURITY_LABEL on\nthe shared nfs_server, silently disabling per-file labeling for both\nthe new and the original mount.\n\nCommit 3815a245b501 (\"security/selinux: fix SECURITY_LSM_NATIVE_LABELS\non reused superblock\") fixed the same problem in\nselinux_sb_clone_mnt_opts().  The reused-superblock path for a plain\nsecond mount now goes through sb_set_mnt_opts rather than\nsb_clone_mnt_opts, so it needs the same treatment: on both\nSE_SBINITIALIZED early exits, set SECURITY_LSM_NATIVE_LABELS in\n*set_kern_flags when the superblock was already using\nSECURITY_FS_USE_NATVE.","summary":"When an NFSv4 export with security labels is mounted a second time, the kernel's SELinux code fails to flag native labels on the reused superblock, so the NFS client clears the security label capability on the shared server. The result is that per-file SELinux labeling is silently turned off for both mounts.","severity":"low","cvss":null,"epss":0.00209,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["linux-kernel","nfs","runtime","selinux"],"not_affected_if":["no-nfsv4-security-label","no-selinux","single-mount"],"how_to_check":null,"fix":null,"status":"open","published_at":"2026-10-23T13:17:28+00:00","first_seen_at":"2026-10-23T21:57:33+00:00","triaged_at":"2026-10-25T04:54:03+00:00","updated_at":"2026-10-25T12:38:50+00:00","category":"runtime","confidence":0.6,"triage":{"at":"2026-10-25T04:54:03Z","model":"claude-haiku-5-5","output":{"fix":"unknown","reach":"local","title":"Linux kernel SELinux: second NFSv4 mount silently disables per-file labeling","impact":"low","summary":"When an NFSv4 export with security labels is mounted a second time, the kernel's SELinux code fails to flag native labels on the reused superblock, so the NFS client clears the security label capability on the shared server. The result is that per-file SELinux labeling is silently turned off for both mounts.","category":"runtime","nicknames":[],"who_cares":["linux-kernel","selinux","nfs"],"confidence":0.6,"needs_auth":"unknown","worst_case":"per-file SELinux labels silently disabled on NFS mounts","analyst_note":"Check the upstream kernel commit and stable backports to find affected and fixed kernel versions; the sources give no version data.","how_to_check":"unknown","needs_analyst":true,"not_affected_if":["no-selinux","no-nfsv4-security-label","single-mount"],"who_is_affected":"Linux hosts that mount NFSv4 filesystems exported with security_label and run SELinux, where the same export is mounted more than once. The sources do not name affected kernel versions, and the impact is loss of labeling rather than code execution.","user_interaction":"no","needs_special_setup":"yes","severity_if_unknown":"low"},"cost_usd":0.000601,"input_tokens":3718,"output_tokens":459,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-2026':14A,17A '-99052':15A,18A '3815a245b501':198C 'alreadi':96C,139C,266C 'already-initi':95C 'call':126C 'cap':175C 'capabl':59B 'clear':55B,173C 'client':54B 'clone':215C,238C 'code':41B 'commit':197C 'cve':13A,16A 'disabl':8A,184C 'earli':148C,251C 'exist':120C 'exit':149C,252C 'export':28B,107C 'fail':42B 'fc':117C 'file':11A,70B,187C 'filesystem':106C 'fix':200C,208C 'flag':44B,159C,261C 'follow':85C 'fs':269C 'get':124C,161C 'goe':229C 'initi':97C,141C 'kern':158C,260C 'kernel':2A,21B,38B,83C 'kflag':165C 'label':12A,31B,46B,58B,72B,93C,110C,155C,170C,177C,188C,204C,257C 'linux':1A,20B,82C 'linux-kernel':19B 'lsm':153C,168C,202C,255C 'mnt':101C,130C,144C,216C,233C,239C 'mount':6A,33B,79B,112C,196C,227C 'nativ':45B,92C,154C,169C,203C,256C 'natv':271C 'need':243C 'new':192C 'nfs':22B,53B,123C,160C,174C,181C 'nfsv4':5A,27B,105C 'opt':102C,131C,145C,217C,234C,240C 'origin':195C 'path':222C 'per':10A,69B,186C 'per-fil':9A,68B,185C 'plain':225C 'preserv':91C 'problem':211C 'rather':235C 'resolv':89C 'result':65B 'return':118C 'reus':49B,206C,220C 'reused-superblock':219C 'root':125C,162C 'runtim':23B 'sb':98C,128C,140C,214C,231C,237C 'sbiniti':250C 'se':249C 'second':4A,35B,114C,226C 'secur':30B,57B,109C,127C,152C,167C,176C,201C,254C,268C 'security/selinux':199C 'see':164C 'selinux':3A,24B,40B,71B,90C,142C,213C 'server':63B,182C 'set':100C,129C,143C,151C,157C,171C,232C,253C,259C 'sget':116C 'share':62B,180C 'silent':7A,74B,183C 'sinc':135C 'superblock':50B,121C,137C,207C,221C,264C 'take':146C 'time':36B,115C 'treatment':246C 'turn':75B 'use':267C,270C 'vulner':86C 'without':150C,166C","nicknames":[],"mitigations":[],"who_affected":"Linux hosts that mount NFSv4 filesystems exported with security_label and run SELinux, where the same export is mounted more than once. The sources do not name affected kernel versions, and the impact is loss of labeling rather than code execution.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-23T13:17:28+00:00","kev":null,"cvss_vector":null,"cvss_by":null,"poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-99052","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-99052","severity":null,"published_at":"2026-10-23T13:17:28+00:00","modified_at":"2026-10-23T13:17:28+00:00","first_seen_at":"2026-10-23T21:57:33+00:00","fetched_at":"2026-10-23T22:29:03+00:00","note":null},{"source":"epss","external_id":"CVE-2026-99052","url":"https://api.first.org/data/v1/epss?cve=CVE-2026-99052","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"}