GHSA-HJ5Q-PP4Q-JPFG
Vulnerability from github – Published: 2026-07-25 12:31 – Updated: 2026-07-27 06:30In the Linux kernel, the following vulnerability has been resolved:
ksmbd: add a WRITE_DAC/WRITE_OWNER check to SMB2 SET_INFO SECURITY
commit cc57232cae23 ("ksmbd: fix FSCTL permission bypass by adding a permission check for FSCTL_SET_SPARSE") added a fp->daccess gate to fsctl_set_sparse and noted that "similar handle-level checks exist in other functions but are missing here." The SMB2 SET_INFO SECURITY arm is one of the missing ones, and the most security-relevant: smb2_set_info_sec() calls set_info_sec() with no per-handle access check.
set_info_sec() (fs/smb/server/smbacl.c) re-permissions the file: it rewrites owner/group/mode via notify_change(), rewrites the POSIX ACL via set_posix_acl(), and on KSMBD_SHARE_FLAG_ACL_XATTR shares removes and rewrites the Windows security descriptor via ksmbd_vfs_set_sd_xattr(). Every other persistent-mutation arm of the sibling handler smb2_set_info_file() checks fp->daccess first (FILE_WRITE_DATA / FILE_DELETE / FILE_WRITE_EA / FILE_WRITE_ATTRIBUTES); the SECURITY arm — which mutates the access control itself — is the only one with no gate.
A client can therefore open a handle with FILE_WRITE_ATTRIBUTES only (no FILE_WRITE_DAC / FILE_WRITE_OWNER) and use SMB2_SET_INFO with InfoType SMB2_O_INFO_SECURITY to rewrite the file's DACL and owner, granting itself access the handle's daccess never carried. Unlike the FSCTL data arms this is a metadata/xattr operation, so there is no FMODE_WRITE VFS backstop — the missing fp->daccess check is the entire gate.
Setting a security descriptor is the WRITE_DAC / WRITE_OWNER operation, so require at least one of those on the handle before re-permissioning the file. -EACCES is mapped to STATUS_ACCESS_DENIED by smb2_set_info().
{
"affected": [],
"aliases": [
"CVE-2026-64394"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-07-25T10:17:22Z",
"severity": "HIGH"
},
"details": "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-\u003edaccess 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-\u003edaccess first (FILE_WRITE_DATA /\nFILE_DELETE / FILE_WRITE_EA / FILE_WRITE_ATTRIBUTES); the SECURITY arm \u2014\nwhich mutates the access control itself \u2014 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\u0027s DACL and owner, granting itself\naccess the handle\u0027s daccess never carried. Unlike the FSCTL data arms this\nis a metadata/xattr operation, so there is no FMODE_WRITE VFS backstop \u2014\nthe missing fp-\u003edaccess 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().",
"id": "GHSA-hj5q-pp4q-jpfg",
"modified": "2026-07-27T06:30:36Z",
"published": "2026-07-25T12:31:34Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-64394"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/0848b1d8b403f530878195dcbe241a2fddb9d0e1"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/44df157a1183a7f746caa970c169255da5ac61f8"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/9ab2ffd3ed3d4ca1667c52de27026ddabc11e537"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/aae600cdaffc6d9ce97645f129799a103a97d06d"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/e6aa731f1b4b3e08caebf66a99f04b22bdab2e99"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/f56535db508ead8dec1c481ad93d7d8acd8f8f1e"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
Sightings
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