CVE intelligence

CVE-2026-63909

Vulnerability intelligence

Published Jul 19, 2026Sources checked Oct 8, 2026

8.1HIGHCVSS out of 10

What this means

Review the available evidence

CVE-2026-63909 and is rated High severity with a CVSS score of 8.1. It is not in the current CISA KEV record we collected. That does not prove exploitation has not occurred.

CISA KEVNot listedBased on the latest collected catalog

EPSS0.6%Estimated 30-day exploitation probability

Ransomware useNot markedCISA KEV ransomware field

Threat actors0Source-linked actor relationships

Overview

What is CVE-2026-63909?

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().

Source: NVD