HighFix available

ksmbd: OOB read regression in smb_check_perm_dacl() ACE-walk loops

Type: advisorySources: OSV

In the Linux kernel, the following vulnerability has been resolved: ksmbd: OOB read regression in smb_check_perm_dacl() ACE-walk loops Commit d07b26f39246 ("ksmbd: require minimum ACE size in smb_check_perm_dacl()") introduced a transposed bounds check: if (offsetof(struct smb_ace, sid) + aces_size < CIFS_SID_BASE_SIZE) Since offsetof(..sid) is 8 and CIFS_SID_BASE_SIZE is 8, this evaluates to `aces_size < 0`. Because `aces_size` is always non-negative, this check becomes dead code and never breaks the loop. Worse, that commit removed the old 4-byte guard, meaning the loop now reads `ace->size` (offset 2) even when `aces_size` is 0-3 bytes. This re-opens a 2-byte heap out-of-bounds (OOB) read past the pntsd allocation during subsequent SMB2_CREATE operations. Fix this by properly transposing the comparison to require at least 16 bytes (8-byte offset + 8-byte SID base), matching the correct form used in smb_inherit_dacl().

Products: Kernel
Affected versions: Not specified
Fixed versions: 6.12.93, 6.18.35, 6.6.143, 7.0.12
CVEs: CVE-2026-63909
Confirmed fixed CVEs: Not specified
Updated in this feed: 7 Nov 2026, 16:43 UTC · Revision 1

Source evidence

ksmbd: OOB read regression in smb_check_perm_dacl() ACE-walk loops

core-osv · Original source

Published 19 Jul 2026, 14:55 UTC

osv:CVE-2026-63909

Kernel

Fixed versions: 6.6.143, 6.12.93, 6.18.35, 7.0.12

Complete source record

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  "url": "https://osv.dev/vulnerability/CVE-2026-63909",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "ksmbd: OOB read regression in smb_check_perm_dacl() ACE-walk loops",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: ksmbd: OOB read regression in smb_check_perm_dacl() ACE-walk loops Commit d07b26f39246 (\"ksmbd: require minimum ACE size in smb_check_perm_dacl()\") introduced a transposed bounds check: if (offsetof(struct smb_ace, sid) + aces_size < CIFS_SID_BASE_SIZE) Since offsetof(..sid) is 8 and CIFS_SID_BASE_SIZE is 8, this evaluates to `aces_size < 0`. Because `aces_size` is always non-negative, this check becomes dead code and never breaks the loop. Worse, that commit removed the old 4-byte guard, meaning the loop now reads `ace->size` (offset 2) even when `aces_size` is 0-3 bytes. This re-opens a 2-byte heap out-of-bounds (OOB) read past the pntsd allocation during subsequent SMB2_CREATE operations. Fix this by properly transposing the comparison to require at least 16 bytes (8-byte offset + 8-byte SID base), matching the correct form used in smb_inherit_dacl().",
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      "modified": "2026-11-01T02:30:52.888650123Z",
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  "source_id": "core-osv",
  "document_id": 519902,
  "published_at": "2026-07-19T14:55:15.06+00:00"
}