RuntimeError: mssql-auth.dll not found. If you are using Entra ID, please ensure it is present.

[mattiasthalen]

Describe the bug

The package complains about mssql-auth.dll, same thing happens if I run it in a venv.

Exception message: RuntimeError: mssql-auth.dll not found. If you are using Entra ID, please ensure it is present.
Stack trace:
Traceback (most recent call last):
  File "C:\Users\MattiasThalén\Repositories\enqore\test.py", line 21, in <module>
    conn = mssql_python.connect(connection_string)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\MattiasThalén\Repositories\enqore\.venv\Lib\site-packages\mssql_python\db_connection.py", line 46, in connect
    conn = Connection(
           ^^^^^^^^^^^
  File "C:\Users\MattiasThalén\Repositories\enqore\.venv\Lib\site-packages\mssql_python\connection.py", line 239, in __init__
    self._conn = ddbc_bindings.Connection(

To reproduce

import mssql_python
import os

host = os.getenv("DESTINATION__CREDENTIALS__HOST")
database = os.getenv("DESTINATION__CREDENTIALS__DATABASE")

connection_string = f"""
Server={host};
Database={database};
Authentication=ActiveDirectoryInteractive;
Encrypt=yes;
"""

conn = mssql_python.connect(connection_string)

Expected behavior

Connection successful.

Further technical details

Python version: 3.11.11
SQL Server version: Fabric Warehouse
Operating system: Windows 11

[dlevy-msft-sql]

Describe the bug

The package complains about mssql-auth.dll, same thing happens if I run it in a venv.

Exception message: RuntimeError: mssql-auth.dll not found. If you are using Entra ID, please ensure it is present.
Stack trace:
Traceback (most recent call last):
  File "C:\Users\MattiasThalén\Repositories\enqore\test.py", line 21, in <module>
    conn = mssql_python.connect(connection_string)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\MattiasThalén\Repositories\enqore\.venv\Lib\site-packages\mssql_python\db_connection.py", line 46, in connect
    conn = Connection(
           ^^^^^^^^^^^
  File "C:\Users\MattiasThalén\Repositories\enqore\.venv\Lib\site-packages\mssql_python\connection.py", line 239, in __init__
    self._conn = ddbc_bindings.Connection(

To reproduce

import mssql_python
import os

host = os.getenv("DESTINATION__CREDENTIALS__HOST")
database = os.getenv("DESTINATION__CREDENTIALS__DATABASE")

connection_string = f"""
Server={host};
Database={database};
Authentication=ActiveDirectoryInteractive;
Encrypt=yes;
"""

conn = mssql_python.connect(connection_string)

Expected behavior

Connection successful.

Further technical details

Python version: 3.11.11 SQL Server version: Fabric Warehouse Operating system: Windows 11

Hi @mattiasthalen - That's an error I haven't seen before. Can you add a call to mssql_python.setup_logging() toward the top of your script and share the output? (Please redact your connection string).

Something like this would be perfect:

import mssql_python
import os

mssql_python.setup_logging()

host = os.getenv("DESTINATION__CREDENTIALS__HOST")
database = os.getenv("DESTINATION__CREDENTIALS__DATABASE")

connection_string = f"""
Server={host};
Database={database};
Authentication=ActiveDirectoryInteractive;
Encrypt=yes;
"""

conn = mssql_python.connect(connection_string)

[mattiasthalen]

239, in __init__
    self._conn = ddbc_bindings.Connection(
                 ^^^^^^^^^^^^^^^^^^^^^^^^^
RuntimeError: mssql-auth.dll not found. If you are using Entra ID, please ensure it is present.
[Python] Error closing database connection: 'Connection' object has no attribute '_conn'
[Python] Error during connection cleanup: 'Connection' object has no attribute '_conn'

[dlevy-msft-sql]

239, in __init__
    self._conn = ddbc_bindings.Connection(
                 ^^^^^^^^^^^^^^^^^^^^^^^^^
RuntimeError: mssql-auth.dll not found. If you are using Entra ID, please ensure it is present.
[Python] Error closing database connection: 'Connection' object has no attribute '_conn'
[Python] Error during connection cleanup: 'Connection' object has no attribute '_conn'

Did it generate any sort of log file or did it not get that far?

[mattiasthalen]

Sorry, I missed it!

# MSSQL-Python Driver Log | Script: test.py | PID: 28356 | Log Level: DEBUG | Python: 3.11.11 | Driver: 1.0.0 | Start: 2025-12-13 00:38:59 | OS: Windows-10-10.0.26200-SP0
Timestamp, ThreadID, Level, Location, Source, Message
2025-12-13 00:38:59.815, 53552, DEBUG, logging.py:374, Python, sanitize_connection_string: Sanitizing connection string (length=221)
2025-12-13 00:38:59.815, 53552, DEBUG, logging.py:374, Python, sanitize_connection_string: Password fields masked
2025-12-13 00:38:59.815, 53552, INFO, logging.py:374, Python, Final connection string: Driver={ODBC Driver 18 for SQL Server};APP=MSSQL-Python;Authentication=ActiveDirectoryInteractive;Database=bronze;Encrypt=yes;Server=[REDACTED].datawarehouse.fabric.microsoft.com
2025-12-13 00:38:59.815, 53552, DEBUG, logging.py:374, Python, process_connection_string: Starting - conn_str_length=221
2025-12-13 00:38:59.815, 53552, DEBUG, logging.py:374, Python, process_connection_string: Split connection string - parameter_count=6
2025-12-13 00:38:59.815, 53552, DEBUG, logging.py:374, Python, process_auth_parameters: Processing 6 connection parameters
2025-12-13 00:38:59.815, 53552, DEBUG, logging.py:374, Python, process_auth_parameters: Interactive authentication detected
2025-12-13 00:38:59.815, 53552, DEBUG, logging.py:374, Python, process_auth_parameters: Windows platform - using native AADInteractive
2025-12-13 00:38:59.815, 53552, DEBUG, logging.py:374, Python, process_auth_parameters: Processing complete - auth_type=None, param_count=6
2025-12-13 00:38:59.815, 53552, DEBUG, logging.py:374, Python, process_connection_string: Connection string processing complete - has_auth=False
2025-12-13 00:38:59.815, 53552, DEBUG, logging.py:374, Python, PoolingManager.enable: Attempting to enable pooling - max_size=100, idle_timeout=600
2025-12-13 00:38:59.815, 53552, INFO, logging.py:374, Python, PoolingManager.enable: Enabling connection pooling - max_size=100, idle_timeout=600 seconds
2025-12-13 00:38:59.815, 53552, INFO, logging.py:374, Python, PoolingManager.enable: Connection pooling enabled successfully
2025-12-13 00:38:59.815, 53552, DEBUG, connection_pool.cpp:122, DDBC, Creating new connection pool
2025-12-13 00:38:59.815, 53552, DEBUG, connection.cpp:22, DDBC, Allocating ODBC environment handle
2025-12-13 00:38:59.818, 53552, DEBUG, connection.cpp:24, DDBC, Function pointers not initialized, loading driver
2025-12-13 00:38:59.818, 53552, DEBUG, ddbc_bindings.cpp:887, DDBC, LoadDriverOrThrowException: Module directory resolved to 'C:\Users\MattiasThalén\Repositories\enqore\.venv\Lib\site-packages\mssql_python'
2025-12-13 00:38:59.818, 53552, DEBUG, ddbc_bindings.cpp:890, DDBC, LoadDriverOrThrowException: Architecture detected as 'x64'
2025-12-13 00:38:59.818, 53552, DEBUG, ddbc_bindings.cpp:899, DDBC, LoadDriverOrThrowException: ODBC driver path determined - path='C:\Users\MattiasThalén\Repositories\enqore\.venv\Lib\site-packages\mssql_python\libs\windows\x64\msodbcsql18.dll'
2025-12-13 00:38:59.818, 53552, DEBUG, ddbc_bindings.cpp:921, DDBC, LoadDriverOrThrowException: mssql-auth.dll not found at 'C:\Users\MattiasThalén\Repositories\enqore\.venv\Lib\site-packages\mssql_python\libs\windows\x64\mssql-auth.dll' - Entra ID authentication will not be available

A search for the dll resulted in C:\Users\MattiasThalén\Repositories\enqore\.venv\Lib\site-packages\mssql_python\libs\windows\x64\mssql-auth.dll

[bewithgaurav]

Hi @mattiasthalen - thank you for reporting this issue & sending over the logs. Really appreciate it!
We've confirmed this is a bug in the driver related to path encoding on Windows.

Root Cause
The issue occurs because the full windows path contains a non-ASCII character (Thalén with é). The C++ code in ddbc_bindings.cpp uses ANSI APIs and incorrect UTF-8 to UTF-16 conversion, which corrupts paths containing non-ASCII characters. As a result, the driver cannot locate mssql-auth.dll even though the file exists at the correct location.

This affects only windows platforms with:

• Non-ASCII characters in their Windows username (like é, ñ, ü, etc.)
• Non-ASCII characters anywhere in the installation path

Workaround
As a temporary workaround, could you try creating your virtual environment in a path that contains only ASCII characters? For example:

mkdir C:\dev\my_project
cd C:\dev\my_project
python -m venv .venv
.\.venv\Scripts\Activate.ps1
pip install mssql-python

This should bypass the encoding issue until we ship the fix. Please let us know if you're still facing issues with workaround.
It will be included in the next release, which will be done by this end of this week.
We will keep this issue updated until this fix is merged & shipped.
Thanks again for your contribution and for your patience!