GHSA-GX4W-GWRQ-P4GH
Vulnerability from github – Published: 2026-08-10 15:33 – Updated: 2026-08-23 15:32In the Linux kernel, the following vulnerability has been resolved:
ksmbd: validate num_subauth when copying ACE in set_ntacl_dacl
set_ntacl_dacl() copies each ACE from the attacker-controlled stored
security descriptor verbatim into the response DACL without checking
sid.num_subauth. The ACE bytes (including an unchecked num_subauth)
originate from an authenticated SMB2_SET_INFO(SecInfo=DACL) that is
stored raw via ksmbd_vfs_set_sd_xattr(); parse_dacl() rejects a bad ACE
with break rather than an error, so parse_sec_desc() still returns
success and the malformed SD reaches the xattr intact.
On a subsequent SMB2_QUERY_INFO(SecInfo=DACL) for an inode carrying a POSIX access ACL, build_sec_desc() -> set_ntacl_dacl() -> set_posix_acl_entries_dacl() walks the copied ACEs and reads
ntace->sid.sub_auth[ntace->sid.num_subauth - 1]
with num_subauth taken straight from the stored SD. Since sub_auth[] is fixed at SID_MAX_SUB_AUTHORITIES (15), a crafted num_subauth (e.g. 255) drives an out-of-bounds heap read of ~1 KB with an offset fully controlled by an authenticated client.
The sibling functions already gate this field: parse_dacl() -- num_subauth == 0 || > SID_MAX_SUB_AUTHORITIES parse_sid() -- num_subauth > SID_MAX_SUB_AUTHORITIES smb_copy_sid() -- min_t(u8, num_subauth, SID_MAX_SUB_AUTHORITIES) set_ntacl_dacl() is the lone inconsistent path that omits the check.
Add the same num_subauth validation in set_ntacl_dacl() before copying the ACE, matching the gate already enforced by parse_dacl().
{
"affected": [],
"aliases": [
"CVE-2026-68100"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-08-10T13:19:54Z",
"severity": "HIGH"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: validate num_subauth when copying ACE in set_ntacl_dacl\n\nset_ntacl_dacl() copies each ACE from the attacker-controlled stored\nsecurity descriptor verbatim into the response DACL without checking\nsid.num_subauth. The ACE bytes (including an unchecked num_subauth)\noriginate from an authenticated SMB2_SET_INFO(SecInfo=DACL) that is\nstored raw via ksmbd_vfs_set_sd_xattr(); parse_dacl() rejects a bad ACE\nwith `break` rather than an error, so parse_sec_desc() still returns\nsuccess and the malformed SD reaches the xattr intact.\n\nOn a subsequent SMB2_QUERY_INFO(SecInfo=DACL) for an inode carrying a\nPOSIX access ACL, build_sec_desc() -\u003e set_ntacl_dacl() -\u003e\nset_posix_acl_entries_dacl() walks the copied ACEs and reads\n\n ntace-\u003esid.sub_auth[ntace-\u003esid.num_subauth - 1]\n\nwith num_subauth taken straight from the stored SD. Since sub_auth[]\nis fixed at SID_MAX_SUB_AUTHORITIES (15), a crafted num_subauth (e.g.\n255) drives an out-of-bounds heap read of ~1 KB with an offset fully\ncontrolled by an authenticated client.\n\nThe sibling functions already gate this field:\n parse_dacl() -- num_subauth == 0 || \u003e SID_MAX_SUB_AUTHORITIES\n parse_sid() -- num_subauth \u003e SID_MAX_SUB_AUTHORITIES\n smb_copy_sid() -- min_t(u8, num_subauth, SID_MAX_SUB_AUTHORITIES)\nset_ntacl_dacl() is the lone inconsistent path that omits the check.\n\nAdd the same num_subauth validation in set_ntacl_dacl() before copying\nthe ACE, matching the gate already enforced by parse_dacl().",
"id": "GHSA-gx4w-gwrq-p4gh",
"modified": "2026-08-23T15:32:56Z",
"published": "2026-08-10T15:33:35Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-68100"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/26cb845e22a00c85bf566337417fa33492395f10"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/47f0b34f6bc98ed85bfdc293e8f3e432ec24958d"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/5acbd3012fd4a7ccfebd91ea6f784120084eb897"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/b6d3cc6a524416dfdb2b47e4bba2e7e20011d056"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/e31fada5143784bc05c7ae44c79eed9b7a2e147e"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/fb3dc8e6da46a1ccad1956cda57de29d9b3033e0"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H",
"type": "CVSS_V3"
}
]
}
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