Unity Linux 20.1050e / 20.1060e / 20.1070e Security Update: kernel (UTSA-2026-151309)

high Nessus Plugin ID 378301

Synopsis

The Unity Linux host is missing one or more security updates.

Description

The Unity Linux 20 host has a package installed that is affected by a vulnerability as referenced in the UTSA-2026-151309 advisory.

In the Linux kernel, the following vulnerability has been resolved:

smb: client: clear setuid/setgid bit on write with cifsacl/modefromsid/posix extensions

When a file has the setuid or setgid bit set and is written to, the VFS strips those bits and issues a setattr with ATTR_KILL_SUID/ATTR_KILL_SGID together with an ATTR_MODE carrying the already-cleared mode.

Both cifs_setattr_unix() and cifs_setattr_nounix() unconditionally dropped ATTR_MODE in that case:

/* skip mode change if it's just for clearing setuid/setgid */ if (attrs->ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) attrs->ia_valid &= ~ATTR_MODE;

This is fine for the default mount, where the mode is only emulated via the DOS read-only attribute and cannot represent the setuid/setgid bits anyway. However, with the cifsacl or modefromsid mount options the mode is stored on the server through an ACL (id_mode_to_cifs_acl()), with the SMB3.1.1 POSIX extensions the mode is sent to the server directly, and with the SMB1 Unix extensions (cifs_setattr_unix) the mode is sent via CIFSSMBUnixSetPathInfo(). In all those cases dropping ATTR_MODE means the cleared mode is never pushed to the server, so the setuid/setgid bit survives the write.

This is a security issue: on local filesystems the setuid bit is stripped when a file is written, but over these cifs.ko mounts the bit persists on the server, potentially allowing an unexpected privilege escalation on subsequent execution.

Fix this in two places:

1. cifs_setattr_nounix(): only take the skip mode change shortcut when the mode is emulated via the DOS read-only attribute (i.e.
neither cifsacl/modefromsid nor the SMB3.1.1 POSIX extensions are in effect), so that the cleared mode is propagated to the server in the ACL / POSIX cases.

2. cifs_setattr_unix(): this function is only called when Unix extensions are in effect, so the mode is always stored on the server. Remove the shortcut entirely so that the cleared mode is always pushed.

Tenable has extracted the preceding description block directly from the Unity Linux security advisory.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

Solution

Update the affected kernel package.

Plugin Details

Severity: High

ID: 378301

File Name: unity_linux_UTSA-2026-151309.nasl

Version: 1.1

Type: Local

Family: Unity Linux Local Security Checks

Published: 11/10/2026

Updated: 11/10/2026

Supported Sensors: Nessus

Risk Information

VPR

Risk Factor: Medium

Score: 4.9

Percentile: 58.39

CVSS v2

Risk Factor: Medium

Base Score: 6.8

Temporal Score: 5

Vector: CVSS2#AV:L/AC:L/Au:S/C:C/I:C/A:C

CVSS Score Source: CVE-2026-89638

CVSS v3

Risk Factor: High

Base Score: 7.8

Temporal Score: 6.8

Vector: CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Temporal Vector: CVSS:3.0/E:U/RL:O/RC:C

Vulnerability Information

Required KB Items: Host/local_checks_enabled, Host/cpu, Host/UOS-Server/release, Host/UOS-Server/rpm-list

Exploit Ease: No known exploits are available

Patch Publication Date: 11/10/2026

Vulnerability Publication Date: 9/11/2026

Reference Information

CVE: CVE-2026-89638

Detections

Analytics