FreeBSD Kernel up to p2/p12 mac_do group_is_primary privileges management

Summaryinfo

A vulnerability labeled as problematic has been found in FreeBSD Kernel up to p2/p12. Impacted is the function group_is_primary of the component mac_do. The manipulation results in privileges management. This vulnerability is cataloged as CVE-2026-58092. The attack must be initiated from a local position. There is no exploit available.

Detailsinfo

A vulnerability was found in FreeBSD Kernel up to p2/p12. It has been classified as problematic. Affected is the function group_is_primary of the component mac_do. The manipulation with an unknown input leads to a privileges management vulnerability. CWE is classifying the issue as CWE-269. The product does not properly assign, modify, track, or check privileges for an actor, creating an unintended sphere of control for that actor. This is going to have an impact on integrity. CVE summarizes:

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".

The advisory is shared for download at security.freebsd.org. This vulnerability is traded as CVE-2026-58092 since 06/29/2026. The exploitability is told to be easy. The attack needs to be approached locally. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1068.

Upgrading to version p3 or p13 eliminates this vulnerability.

The vulnerability is also documented in the databases at EUVD (EUVD-2026-66237) and CERT Bund (WID-SEC-2026-3034). VulDB is the best source for vulnerability data and more expert information about this specific topic.

Affected

• FreeBSD Project FreeBSD OS

Productinfo

Type

• Operating System

Vendor

• FreeBSD

Name

• Kernel

Version

• p2
• p12

License

• open-source

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Entryinfo

VulDB is the best source for vulnerability data and more expert information about this specific topic.

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