Progressive Robot hMailServer up to 6.3.7 Plugin Loading hMailServer.exe privileges management

Summaryinfo

A vulnerability described as critical has been identified in Progressive Robot hMailServer up to 6.3.7. Affected is an unknown function of the file hMailServer.exe of the component Plugin Loading. The manipulation results in privileges management. This vulnerability is known as CVE-2026-126607. Attacking locally is a requirement. No exploit is available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability, which was classified as critical, was found in Progressive Robot hMailServer up to 6.3.7. Affected is an unknown code block of the file hMailServer.exe of the component Plugin Loading. 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 confidentiality, integrity, and availability. CVE summarizes:

Progressive Robot hMailServer 6.2.3 through 6.3.7 on Windows, with a MySQL or MariaDB database, hands the bundled MariaDB Connector/C the folder of its authentication plugins (the plugin folder in the installation's Bin folder) as Latin-1 bytes, which the client reads in the system's ANSI code page when it builds a plugin's path and loads the plugin with LoadLibraryExA, which allows a local authenticated user to execute code as the hMailServer service's account (LocalSystem, or the service's virtual account for a new installation from 6.3.4) by creating the folder those bytes name in the code page and placing in it a DLL with a plugin's name, when the installation folder's path holds a character between U+0080 and U+00FF whose byte the code page reads as another character, and none above U+00FF, and the user can create that other folder (by default any authenticated user may create a folder directly under the root of the system drive). The server converted the path with the C runtime's wcstombs_s in the C locale, which writes each character up to U+00FF as the byte of the same value: on code page 1252 those bytes are the same letters, while on another code page, such as 1251, or on a UTF-8 code page, they name another folder. The client loads the plugin the database server names in its greeting, unless it is built in, and any plugin the server names in an authentication switch, and tries again at each connection while a load fails, so with a MySQL 8.0 or later server, whose greeting names caching_sha2_password by default, the DLL is loaded at the next connection the service makes, whatever plugin the database account uses; a DLL's entry point runs when it is loaded. A path holding any character above U+00FF was handed over as an empty string, whatever the code page, from which the client makes a plugin's name at the root of the current drive: for the service, whose current folder is System32, that is the root of the system drive, where by default only administrators can create a file, but the server's own database commands (hMailServer.exe --check-database, --upgrade-database and the others from 6.3.4, and the /Debug and /Test console modes from 6.2.3) run in the folder they are started from - the product tells administrators to run them from an elevated prompt in the Bin folder, and the setup of 6.3.4 and 6.3.5 ran two or three of them itself with the Bin folder as their working folder for a new installation with an external database - so a DLL that a local authenticated user placed under a plugin's name at the root of a drive other users may write, such as a FAT or exFAT volume, was loaded into the administrator's process at the command's first connection to a MySQL 8.0 or later server. 6.3.8 fixes both cases: it hands the folder in the code page's bytes or by its short (8.3) name, and where neither can be written, a folder under the Windows system folder that holds no plugin and that only administrators can create, or else refuses the connection before attempting it; it never hands the empty value or a folder the current drive completes. The configuration is not the default: the default installation folder, under Program Files, is ASCII. Linux builds set no plugin folder and are not affected.

The advisory is shared for download at gitlab.com. This vulnerability is traded as CVE-2026-126607 since 11/11/2026. 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 6.3.8 eliminates this vulnerability.

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

Productinfo

Type

• Mail Server Software

Vendor

• Progressive Robot

Name

• hMailServer

Version

• 6.3.0
• 6.3.1
• 6.3.2
• 6.3.3
• 6.3.4
• 6.3.5
• 6.3.6
• 6.3.7

CPE 2.3info

• 🔒
• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒
• 🔒

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

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

Discussion