{"id":"CVE-2026-99131","kind":"vulnerability","aliases":["CVE-2026-99131"],"related":[],"title":"Linux kernel XFS: capability check lets users bypass group quota limits","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nxfs: fix capability check in xfs\n\nAn user reported a bug where he managed to evade group's quota\nby changing a file's gid to a different group id the same user\nbelonged to, even though quotas were enforced on both gids and the\nfile's size was big enough to exceed the quota's hardlimit.\n\nCommit eba0549bc7d1 replaced a capable() call by a\nhas_capability_noaudit() to prevent unnecessary selinux audit messages.\nTurns out that both calls have slightly different semantics even though\ntheir documentation seems similar. Where in a nutshell:\n\ncapable() - Tests the task's effective credentials\nhas_ns_capability_noaudit() - Tests the task's real credentials\n\nThis most of the time has no practical difference but in some cases like\nchanging attrs (specifically group id in this case) through a NFS client\nthis will allow the quota code to use XFS_QMOPT_FORCE_RES, effectively\nbypassing quota accounting checks.\n\nUsing instead ns_capable_noaudit() should fix this issue and prevent\nselinux audit messages.\n\nThis also fix the remaining calls to has_capability_noaudit()","summary":"The Linux kernel XFS filesystem checked the wrong credential set for a capability, so a user could change a file's group ID to another group they belong to and skip quota accounting. The result is that a user can exceed a group's quota hard limit.","severity":"unknown","cvss":null,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["infrastructure","kernel","linux","nfs","self-hosted","xfs"],"not_affected_if":["no-nfs-client-access","no-xfs-quotas"],"how_to_check":"- unknown","fix":"- unknown","status":"open","published_at":"2026-10-28T11:17:32+00:00","first_seen_at":"2026-10-28T11:32:35+00:00","triaged_at":"2026-10-28T11:36:15+00:00","updated_at":"2026-10-28T11:36:15+00:00","category":"infrastructure","confidence":0.6,"triage":{"at":"2026-10-28T11:36:15Z","model":"claude-haiku-5-5","output":{"fix":"- unknown","reach":"local","title":"Linux kernel XFS: capability check lets users bypass group quota limits","impact":"low","summary":"The Linux kernel XFS filesystem checked the wrong credential set for a capability, so a user could change a file's group ID to another group they belong to and skip quota accounting. The result is that a user can exceed a group's quota hard limit.","category":"infrastructure","nicknames":[],"who_cares":["linux","xfs","kernel","nfs","self-hosted"],"confidence":0.6,"needs_auth":"yes","worst_case":"quota limits bypassed; group disk accounting can be evaded","analyst_note":"Find the fixed kernel versions and stable backport commits from the NVD entry at https://nvd.nist.gov/vuln/detail/CVE-2026-99131 and the kernel git commit eba0549bc7d1 reference.","how_to_check":"- unknown","needs_analyst":true,"not_affected_if":["no-xfs-quotas","no-nfs-client-access"],"who_is_affected":"Systems running a Linux kernel with XFS filesystems and group quotas enforced, particularly where file attributes are changed through an NFS client. Systems without XFS quotas enforced, or that do not use XFS, are unlikely to be affected. The sources do not give affected kernel version ranges.","user_interaction":"no","needs_special_setup":"yes","severity_if_unknown":"unknown"},"cost_usd":0.00061,"input_tokens":3598,"output_tokens":500,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-2026':13A,16A '-99131':14A,17A 'account':58B,234C 'allow':221C 'also':251C 'anoth':50B 'attr':208C 'audit':155C,248C 'belong':53B,116C 'big':132C 'bug':93C 'bypass':8A,232C 'call':145C,161C,255C 'capabl':4A,38B,85C,144C,149C,176C,185C,239C,258C 'case':205C,214C 'chang':43B,103C,207C 'check':5A,31B,86C,235C 'client':218C 'code':224C 'commit':140C 'could':42B 'credenti':34B,182C,192C 'cve':12A,15A 'differ':110C,164C,201C 'document':169C 'eba0549bc7d1':141C 'effect':181C,231C 'enforc':122C 'enough':133C 'evad':98C 'even':118C,166C 'exceed':66B,135C 'file':45B,105C,128C 'filesystem':30B 'fix':84C,242C,252C 'follow':78C 'forc':229C 'gid':107C,125C 'group':9A,47B,51B,68B,99C,111C,210C 'hard':71B 'hardlimit':139C 'host':24B 'id':48B,112C,211C 'infrastructur':18B 'instead':237C 'issu':244C 'kernel':2A,19B,28B,76C 'let':6A 'like':206C 'limit':11A,72B 'linux':1A,20B,27B,75C 'manag':96C 'messag':156C,249C 'nfs':21B,217C 'noaudit':150C,186C,240C,259C 'ns':184C,238C 'nutshel':175C 'practic':200C 'prevent':152C,246C 'qmopt':228C 'quota':10A,57B,70B,101C,120C,137C,223C,233C 'real':191C 'remain':254C 'replac':142C 'report':91C 'res':230C 'resolv':82C 'result':60B 'seem':170C 'self':23B 'self-host':22B 'selinux':154C,247C 'semant':165C 'set':35B 'similar':171C 'size':130C 'skip':56B 'slight':163C 'specif':209C 'task':179C,189C 'test':177C,187C 'though':119C,167C 'time':197C 'turn':157C 'unnecessari':153C 'use':226C,236C 'user':7A,41B,64B,90C,115C 'vulner':79C 'wrong':33B 'xfs':3A,25B,29B,83C,88C,227C","nicknames":[],"mitigations":[],"who_affected":"Systems running a Linux kernel with XFS filesystems and group quotas enforced, particularly where file attributes are changed through an NFS client. Systems without XFS quotas enforced, or that do not use XFS, are unlikely to be affected. The sources do not give affected kernel version ranges.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-28T11:17:32+00:00","kev":null,"cvss_vector":null,"cvss_by":null,"poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-99131","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-99131","severity":null,"published_at":"2026-10-28T11:17:32+00:00","modified_at":"2026-10-28T11:17:32+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"}