{"api_version":"1","generated_at":"2026-11-10T17:21:27+00:00","cve":"CVE-2026-99131","urls":{"html":"https://cve.report/CVE-2026-99131","api":"https://cve.report/api/cve/CVE-2026-99131.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-99131","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-99131"},"summary":{"title":"xfs: fix capability check in xfs","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()","state":"PUBLISHED","assigner":"Linux","published_at":"2026-10-28 11:17:32","updated_at":"2026-10-31 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Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-99131","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected eba0549bc7d100691c13384b774346b8aa9cf9a9 29f994db0447104a7a52fb6495193c80007cb66a git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected eba0549bc7d100691c13384b774346b8aa9cf9a9 e84bfb08016496ec5ce09a5ef9c813f23c060781 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected eba0549bc7d100691c13384b774346b8aa9cf9a9 87881f816ab721d8a727cba20c36b9c71b489c8e git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected eba0549bc7d100691c13384b774346b8aa9cf9a9 19a1a22029ad3ae3604c763af6bd1195cb73648f git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 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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()"}],"metrics":[{"cvssV3_1":{"baseScore":8.2,"baseSeverity":"HIGH","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H","version":"3.1"},"scenarios":[{"lang":"en","value":"AV:N - An NFSv4 COMPOUND/SETATTR request carries FATTR4_OWNER_GROUP; nfsd4_decode_setattr() sets ATTR_GID, and nfsd4_setattr()->nfsd_setattr()->notify_change()->xfs_vn_setattr() reaches the patched xfs_setattr_nonsize(). NFS is routable, so the vector is Network.\nAC:L - The attacker controls the deterministic sequence: AUTH_SYS credentials assert both groups, NFS WRITE fills the source group's quota, and SETATTR moves each file to the over-limit destination group. No race or external state transition is required.\nPR:N - svcauth_unix_accept() accepts the uid, gid, and supplementary groups asserted in an AUTH_SYS RPC without account verification, and nfsd_setuser() installs them as subjective credentials. chgrp_ok() then requires only the asserted owner identity and destination-group membership.\nUI:N - The remote client creates and fills the file and sends the SETATTR group change itself; neither nfsd_setattr() nor xfs_setattr_nonsize() requires a separate victim action.\nS:U - xfs_trans_dqresv() skips a quota check and xfs_qm_vop_chown() updates dquots within the same host XFS security authority; no VM, sandbox, or other security boundary is crossed.\nC:N - XFS_QMOPT_FORCE_RES only bypasses the limit branch in xfs_trans_dqresv(), after which quota counters and inode ownership are updated; the path performs no out-of-bounds read or disclosure of kernel or other-file data.\nI:L - With XFS_QMOPT_FORCE_RES set, xfs_trans_dqresv() omits the hard-limit test and xfs_qm_vop_chown() charges blocks and inodes to an already over-limit group. This defeats quota policy and modifies resource accounting, but provides no arbitrary write or control over other users' file contents.\nA:H - xfs_qm_vop_chown() debits the source dquot and, after forced reservation, credits the already over-limit destination; repeating NFS writes and group changes can consume the entire XFS volume. Full-volume exhaustion denies allocations to all users and services on that filesystem."}]}],"providerMetadata":{"dateUpdated":"2026-10-31T12:43:34.118Z","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux"},"references":[{"url":"https://git.kernel.org/stable/c/29f994db0447104a7a52fb6495193c80007cb66a"},{"url":"https://git.kernel.org/stable/c/e84bfb08016496ec5ce09a5ef9c813f23c060781"},{"url":"https://git.kernel.org/stable/c/87881f816ab721d8a727cba20c36b9c71b489c8e"},{"url":"https://git.kernel.org/stable/c/19a1a22029ad3ae3604c763af6bd1195cb73648f"},{"url":"https://git.kernel.org/stable/c/7809ac0161c7c5f52ed348fb1ec683b2b454a83e"},{"url":"https://git.kernel.org/stable/c/e2f62a9744ebad3bcb6347a648e615026e9efeff"}],"title":"xfs: fix capability check in xfs","x_generator":{"engine":"bippy-1.2.0"}}},"cveMetadata":{"assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","assignerShortName":"Linux","cveId":"CVE-2026-99131","datePublished":"2026-10-28T10:34:45.102Z","dateReserved":"2026-09-25T10:25:14.394Z","dateUpdated":"2026-10-31T12:43:34.118Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-10-28 11:17:32","lastModifiedDate":"2026-10-31 13:17:56","problem_types":[],"metrics":{"cvssMetricV31":[{"source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","type":"Secondary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H","baseScore":8.2,"baseSeverity":"HIGH","attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"NONE","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"NONE","integrityImpact":"LOW","availabilityImpact":"HIGH"},"exploitabilityScore":3.9,"impactScore":4.2}]},"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"99131","Ordinal":"1","Title":"xfs: fix capability check in xfs","CVE":"CVE-2026-99131","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"99131","Ordinal":"1","NoteData":"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()","Type":"Description","Title":"xfs: fix capability check in xfs"}]}}}