FreeBSD : FreeBSD -- Unauthorized credential switching (55fbe7b1-a0fe-11f1-ae1f-bc241121aa0a)

high Nessus Plugin ID 340055

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Synopsis

The remote FreeBSD host is missing one or more security-related updates.

Description

The version of FreeBSD installed on the remote host is prior to tested version. It is, therefore, affected by a vulnerability as referenced in the 55fbe7b1-a0fe-11f1-ae1f-bc241121aa0a advisory.

In FreeBSD 15.0, the kernel structure used to represent user credentials changed: previously the primary group ID was stored in the first element of the array containing the list of supplementary group IDs, whereas now the primary group ID is stored in a dedicated field. This change was largely internal to the kernel and not user-visible.
One function, group_is_primary(), was not properly updated as a part of this transition. This function is used by mac_do to determine the primary group ID of the credential after applying a transition rule, used when the rule target does not explicitly specify a group.
As a result, with certain mac_do rules, it is possible for a credential switch to incorrectly set the primary group ID to the ID stored in the first element of the original credential's supplementary group array. If the list of supplementary groups is empty, this value will be 0, corresponding to the wheel group.
For example, a rule such as uid=1001>uid=1002 can be abused to set the primary group ID to 0 even if the process did not originally belong to group 0.
Certain mac_do rules can be abused to set a process' group ID to 0. Note however, that the rule must apply to the caller in order for the bug to be triggered, e.g., given the ruleset uid=1001>uid=1002, the user must have user ID 1001 in order to trigger the bug.
Further, logged-in users will in general have a non-empty supplementary group list, in which case the bug can at worst be used to set the credential's first supplementary group ID as its primary group ID.
Processes must explicitly remove themselves from all supplementary groups, using the privileged setgroups(2) system call, in order to exploit the bug to set 0 as the primary group ID.
Since membership in group 0 is often used to enable controlled privilege escalation, the bug might be further exploitable to obtain root privileges, depending on the system configuration. For instance, a ruleset such as the following could be exploited by a process running as user 1001 and with an empty supplementary group list:
uid=1001>uid=1002;gid=0>uid=0.

Tenable has extracted the preceding description block directly from the FreeBSD 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 packages.

Plugin Details

Severity: High

ID: 340055

File Name: freebsd_pkg_55fbe7b1a0fe11f1ae1fbc241121aa0a.nasl

Version: 1.2

Type: Local

Family: FreeBSD Local Security Checks

Published: 8/26/2026

Updated: 8/28/2026

Configuration: Enable paranoid mode

Supported Sensors: Nessus

Risk Information

VPR

Risk Factor: High

Score: 7

Percentile: 98.2

CVSS v2

Risk Factor: Medium

Base Score: 6

Temporal Score: 4.4

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

CVSS Score Source: CVE-2026-58092

CVSS v3

Risk Factor: High

Base Score: 8.1

Temporal Score: 7.1

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

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

Vulnerability Information

CPE: cpe:/o:freebsd:freebsd, p-cpe:/a:freebsd:freebsd:freebsd-kernel

Required KB Items: Settings/ParanoidReport, Host/local_checks_enabled, Host/FreeBSD/release, Host/FreeBSD/pkg_info

Exploit Ease: No known exploits are available

Patch Publication Date: 8/26/2026

Vulnerability Publication Date: 8/26/2026

Reference Information

CVE: CVE-2026-58092

Detections

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