# CVE-2026-63909: linux: In the Linux kernel, the following vulnerability has been resolved:  ksmbd: OOB read regression in smb_check_perm_dac...

CVE-2026-63909 is fixed in linux on 1 platform, first by DEBIAN-CVE-2026-63909, released July 20, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-63909
- Priority: High
- CVSS: 8.1 (high)
- EPSS: 0.0063
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jul 19, 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().

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.94-1 | [DEBIAN-CVE-2026-63909](https://patchblox.com/security/data/fix/linux/debian-cve-2026-63909.md) | Jul 20, 2026 |
| Linux | linux Debian 14 | 7.0.12-1 | [DEBIAN-CVE-2026-63909](https://patchblox.com/security/data/fix/linux/debian-cve-2026-63909.md) | Jul 20, 2026 |

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Data as of 2026-11-10T13:56:55Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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