Understanding LDAP `objectGUID` Encoding in Mattermost

Marco Kundt

Updated June 16, 2026 14:58

Problem

When Mattermost is configured with LDAP authentication using the recommended objectguid attribute as the IDAttribute, the value is stored in the users database table in the authdata column. This value is encoded in a specific binary format that differs from the standard GUID representation.

Administrators may need to understand this encoding when manual modification of the authdata column is required, such as when instructed by Mattermost support.

Symptoms

When viewing the authdata column in the database, the objectGUID appears as:

A sequence of escaped hexadecimal bytes instead of the familiar GUID format
A 16-byte binary value that does not match the standard GUID representation
Raw data that requires understanding of little-endian encoding to interpret

Solution

To properly handle LDAP objectGUID values in the Mattermost database, it's important to understand the little-endian binary encoding format used for storage.

Understanding the Encoding

The encoding is a little-endian binary representation of a GUID (Globally Unique Identifier), which is how objectGUID values are stored in Active Directory databases. The GUID is stored as a 16-byte binary value, and when exported or viewed in raw form (e.g., in a database dump), it appears as a sequence of escaped hexadecimal bytes.

GUID Structure and Conversion

A standard GUID such as 1ac95e2a-33c9-4bac-9629-610836a88152 is broken down into five components:

1ac95e2a → 4 bytes
33c9 → 2 bytes
4bac → 2 bytes
96 and 29 → 2 bytes
61 08 36 a8 81 52 → 6 bytes

In little-endian format, the first three components are byte-reversed, while the last two components are not. The binary representation becomes:

2a 5e c9 1a c9 33 ac 4b 96 29 61 08 36 a8 81 52

Important: This procedure should only be performed when explicitly instructed by Mattermost support staff. Incorrect database modifications can cause authentication failures, data corruption, or system instability. Always create a complete database backup before making any manual changes.