CVE-2026-63909

Published: July 22, 2026Last modified: July 22, 2026

Description

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().

Severity score breakdown

Status

References

• https://git.kernel.org/stable/c/0e60dafe97eca61721f3db456f97d97a80c6c8ae
• https://git.kernel.org/stable/c/0fe08c5776a798f46df1fd74b331be26bdd644d6
• https://git.kernel.org/stable/c/4f7c131d2bdd7cd64b96f60d10be5ea72253f520
• https://git.kernel.org/stable/c/5500ba1d410aed1eded3eb04a76b10cfb4409334
• https://git.kernel.org/stable/c/94215d55b09445993929f4fc966061d61de74929
• https://git.kernel.org/stable/c/d333af32e4451285e427f2d9c29de3a39f6f6d48
• https://git.kernel.org/stable/c/f6324b4240cf0b26a84c33f68a1222d727ff4af2