{"cve":"CVE-2026-64394","nvd":{"published":"2026-07-25T10:17:22.790","modified":"2026-09-04T15:31:40.967","status":"Analyzed","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: add a WRITE_DAC/WRITE_OWNER check to SMB2 SET_INFO SECURITY\n\ncommit cc57232cae23 (\"ksmbd: fix FSCTL permission bypass by adding a\npermission check for FSCTL_SET_SPARSE\") added a fp->daccess gate to\nfsctl_set_sparse and noted that \"similar handle-level checks exist in other\nfunctions but are missing here.\" The SMB2 SET_INFO SECURITY arm is one of\nthe missing ones, and the most security-relevant: smb2_set_info_sec() calls\nset_info_sec() with no per-handle access check.\n\nset_info_sec() (fs/smb/server/smbacl.c) re-permissions the file: it\nrewrites owner/group/mode via notify_change(), rewrites the POSIX ACL via\nset_posix_acl(), and on KSMBD_SHARE_FLAG_ACL_XATTR shares removes and\nrewrites the Windows security descriptor via ksmbd_vfs_set_sd_xattr().\nEvery other persistent-mutation arm of the sibling handler\nsmb2_set_info_file() checks fp->daccess first (FILE_WRITE_DATA /\nFILE_DELETE / FILE_WRITE_EA / FILE_WRITE_ATTRIBUTES); the SECURITY arm —\nwhich mutates the access control itself — is the only one with no gate.\n\nA client can therefore open a handle with FILE_WRITE_ATTRIBUTES only (no\nFILE_WRITE_DAC / FILE_WRITE_OWNER) and use SMB2_SET_INFO with InfoType\nSMB2_O_INFO_SECURITY to rewrite the file's DACL and owner, granting itself\naccess the handle's daccess never carried. Unlike the FSCTL data arms this\nis a metadata/xattr operation, so there is no FMODE_WRITE VFS backstop —\nthe missing fp->daccess check is the entire gate.\n\nSetting a security descriptor is the WRITE_DAC / WRITE_OWNER operation, so\nrequire at least one of those on the handle before re-permissioning the\nfile. -EACCES is mapped to STATUS_ACCESS_DENIED by smb2_set_info().","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","score":8.8},"cwes":[],"references":["https://git.kernel.org/stable/c/0848b1d8b403f530878195dcbe241a2fddb9d0e1","https://git.kernel.org/stable/c/44df157a1183a7f746caa970c169255da5ac61f8","https://git.kernel.org/stable/c/9ab2ffd3ed3d4ca1667c52de27026ddabc11e537","https://git.kernel.org/stable/c/aae600cdaffc6d9ce97645f129799a103a97d06d","https://git.kernel.org/stable/c/e6aa731f1b4b3e08caebf66a99f04b22bdab2e99"],"products":["linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-19T22:46:40.600842820+00:00"},"epss":{"cve":"CVE-2026-64394","score":0.0047,"percentile":0.40652,"date":"2026-10-31"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}