# CVE-2026-68100: ksmbd: validate num_subauth when copying ACE in set_ntacl_dacl

CVE-2026-68100 is fixed in 2 products on 1 platform, first by DEBIAN-CVE-2026-68100, released August 11, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-68100
- Priority: High
- CVSS: 8.1 (Moderate)
- EPSS: 0.0044
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Aug 10, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-68100

## Description

In the Linux kernel, the following vulnerability has been resolved:  ksmbd: validate num_subauth when copying ACE in set_ntacl_dacl  set_ntacl_dacl() copies each ACE from the attacker-controlled stored security descriptor verbatim into the response DACL without checking sid.num_subauth. The ACE bytes (including an unchecked num_subauth) originate from an authenticated SMB2_SET_INFO(SecInfo=DACL) that is stored raw via ksmbd_vfs_set_sd_xattr(); parse_dacl() rejects a bad ACE with `break` rather than an error, so parse_sec_desc() still returns success and the malformed SD reaches the xattr intact.  On a subsequent SMB2_QUERY_INFO(SecInfo=DACL) for an inode carrying a POSIX access ACL, build_sec_desc() -> set_ntacl_dacl() -> set_posix_acl_entries_dacl() walks the copied ACEs and reads      ntace->sid.sub_auth[ntace->sid.num_subauth - 1]  with num_subauth taken straight from the stored SD. Since sub_auth[] is fixed at SID_MAX_SUB_AUTHORITIES (15), a crafted num_subauth (e.g. 255) drives an out-of-bounds heap read of ~1 KB with an offset fully controlled by an authenticated client.  The sibling functions already gate this field:   parse_dacl()    -- num_subauth == 0 || > SID_MAX_SUB_AUTHORITIES   parse_sid()     -- num_subauth > SID_MAX_SUB_AUTHORITIES   smb_copy_sid()  -- min_t(u8, num_subauth, SID_MAX_SUB_AUTHORITIES) set_ntacl_dacl() is the lone inconsistent path that omits the check.  Add the same num_subauth validation in set_ntacl_dacl() before copying the ACE, matching the gate already enforced by parse_dacl().

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 6.1.187-1 | [DEBIAN-CVE-2026-68100](https://patchblox.com/security/data/fix/linux/debian-cve-2026-68100.md) | Aug 11, 2026 |
| Linux | linux Debian 13.5 (trixie) | 6.12.101-1 | [DEBIAN-CVE-2026-68100](https://patchblox.com/security/data/fix/linux/debian-cve-2026-68100.md) | Aug 11, 2026 |
| Linux | linux Debian 14 | 7.1.6-1 | [DEBIAN-CVE-2026-68100](https://patchblox.com/security/data/fix/linux/debian-cve-2026-68100.md) | Aug 11, 2026 |
| Linux | linux-6.12 Debian 12.15 (bookworm) | 6.12.101-1~deb12u1 | [DEBIAN-CVE-2026-68100](https://patchblox.com/security/data/fix/linux/debian-cve-2026-68100.md) | Aug 11, 2026 |

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Data as of 2026-11-08T06:59:42Z 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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