PT-2026-61226 · Linux · Linux

CVE-2026-63909 · Published 2026-07-19 · Updated 2026-07-19

Mitre

CVSS v3.1

8.1

High

Base vector

AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H

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().

Fix

Related Identifiers

CVE-2026-63909

Affected Products

Linux

References · 8

• https://nvd.nist.gov/vuln/detail/CVE-2026-63909 · Security Note
• https://git.kernel.org/stable/c/f6324b4240cf0b26a84c33f68a1222d727ff4af2 · Note
• https://git.kernel.org/stable/c/5500ba1d410aed1eded3eb04a76b10cfb4409334 · Note
• https://git.kernel.org/stable/c/d333af32e4451285e427f2d9c29de3a39f6f6d48 · Note
• https://git.kernel.org/stable/c/0fe08c5776a798f46df1fd74b331be26bdd644d6 · Note
• https://git.kernel.org/stable/c/4f7c131d2bdd7cd64b96f60d10be5ea72253f520 · Note
• https://git.kernel.org/stable/c/0e60dafe97eca61721f3db456f97d97a80c6c8ae · Note
• https://git.kernel.org/stable/c/94215d55b09445993929f4fc966061d61de74929 · Note