# CVE-2026-99110: smb: client: fix heap overflow in cifs_do_set_acl()

CVE-2026-99110 is fixed in linux on 1 platform, first by DEBIAN-CVE-2026-99110, released November 3, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-99110
- Priority: High
- CVSS: 7.8 (Important)
- EPSS: 0.0013
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 28, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-99110

## Description

In the Linux kernel, the following vulnerability has been resolved:  smb: client: fix heap overflow in cifs_do_set_acl()  cifs_set_acl() validates ACL size using posix_acl_xattr_size():          4 + (count * 8)  // 4-byte header + 8 bytes per ACE  cifs_do_set_acl() then calls posix_acl_to_cifs() to write the CIFS wire format into the same buffer:          6 + (count * 10)  // 6-byte header + 10 bytes per ACE  An ACL that passes the xattr-based check in cifs_set_acl() can overflow the heap when posix_acl_to_cifs() writes the larger CIFS format.  Validate the CIFS format size against the remaining buffer space and USHRT_MAX before converting--data_count is __u16, so sizes above USHRT_MAX truncate the on-wire packet length, causing the server to apply a partial ACL.  Replace MaxDataCount = 1000 with min(CIFSMaxBufSize, USHRT_MAX).

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.115-2 | [DEBIAN-CVE-2026-99110](https://patchblox.com/security/data/fix/linux/debian-cve-2026-99110.md) | Nov 3, 2026 |
| Linux | linux Debian 14 | 7.2.13-1 | [DEBIAN-CVE-2026-99110](https://patchblox.com/security/data/fix/linux/debian-cve-2026-99110.md) | Nov 3, 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 Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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