CVE-2026-63909

High

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().

Package Linux Kernel
Published 2026-07-19
Last modified 2026-07-27
CVSS version 3.1
Patch available
Yes

CVSS 3.1 score

8.1

out of 10
High
Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
High
Vector string
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H

Affected versions

Linux kernel versions 6.6.140, 6.12.84, 6.18.25, 7.0.2 and later are affected. Fixed in 6.6.143, 6.12.93, 6.18.35, 7.0.12 and their respective stable series.

Affected from
≥ 6.6.140 ≥ 6.12.84 ≥ 6.18.25 ≥ 7.0.2
Fixed in
✓ 6.6.143 6.6.x ✓ 6.12.93 6.12.x ✓ 6.18.35 6.18.x ✓ 7.0.12 7.0.x

References

7 total
Showing 5 of 7 references View all on NVD

Frequently asked questions

  • What is CVE-2026-63909?

    CVE-2026-63909 is a High severity Linux kernel vulnerability with a CVSS score of 8.1 out of 10 . It affects Linux kernel versions from 6.6.140 onward and has been patched in 6.6.143, 6.12.93, 6.18.35 and others. CVE-2026-63909 has not been confirmed as actively exploited and is not listed in the CISA KEV catalog.

  • What is the CVSS score for CVE-2026-63909?

    CVE-2026-63909 has a CVSS score of 8.1 out of 10, rated High severity (CVSS 3.1). The vector string is CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H .

  • Is there a patch available for CVE-2026-63909?

    Yes. CVE-2026-63909 has been patched. Fixed versions include 6.6.143, 6.12.93, 6.18.35 and others. If you are running Linux kernel 6.6.140 or later up to the fix versions, apply the relevant patch for your kernel branch.

  • Is CVE-2026-63909 actively exploited?

    No. CVE-2026-63909 has not been confirmed as actively exploited. It is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog.

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