Fix MySQL Access Denied Error (0x80004005)

As a server administrator, when I see MySqlConnector.MySqlException (0x80004005): Access Denied for User, I know it's an authentication issue. This usually happens due to incorrect credentials, missing privileges, host restrictions, or authentication plugin mismatches.

I follow these steps to diagnose and fix the issue:

This guide is written from a server administrator's perspective and includes commands that require root or sudo privileges.

Verify the Correct Username and Password

First, I check if the credentials in the application's connection string are correct.

Manual Authentication Test

I try logging into MySQL manually:

mysql -u myuser -p

If authentication fails, I check if the user exists:

SELECT user, host FROM mysql.user;

If myuser is not listed, I create it:

CREATE USER 'myuser'@'localhost' IDENTIFIED BY 'mypassword';
GRANT ALL PRIVILEGES ON *.* TO 'myuser'@'localhost' WITH GRANT OPTION;
FLUSH PRIVILEGES;

If authentication fails but the user exists, I reset the password:

ALTER USER 'myuser'@'localhost' IDENTIFIED BY 'newpassword';
FLUSH PRIVILEGES;

Then, I restart MySQL to ensure changes apply:

sudo systemctl restart mysql

Check Remote Access Settings

If the application connects from another server, MySQL may be blocking the remote connection.

Grant Remote Access

I check if the user is restricted to localhost:

SELECT user, host FROM mysql.user WHERE user = 'myuser';

If the host is localhost, I allow remote access:

GRANT ALL PRIVILEGES ON *.* TO 'myuser'@'%' IDENTIFIED BY 'mypassword';
FLUSH PRIVILEGES;

Check MySQL Bind Address

If MySQL only listens on 127.0.0.1, remote connections won't work. I check my.cnf:

cat /etc/mysql/mysql.conf.d/mysqld.cnf

If I see:

bind-address = 127.0.0.1

I change it to:

bind-address = 0.0.0.0

Then restart MySQL:

sudo systemctl restart mysql

Ensure the Correct Authentication Plugin

Newer MySQL versions (8.0+) use caching_sha2_password, which some connectors don't support. I check:

SELECT user, host, plugin FROM mysql.user WHERE user = 'myuser';

If plugin is caching_sha2_password, but the application requires mysql_native_password, I fix it:

ALTER USER 'myuser'@'%' IDENTIFIED WITH mysql_native_password BY 'mypassword';
FLUSH PRIVILEGES;

Then I update MySQL Connector to ensure compatibility.

Ensure MySQL Connector Is Updated

If the application uses an old MySQL Connector, it may not support the new authentication method. I update the connector:

C# (.NET):
Install-Package MySql.Data -Version 8.0.33
Python (MySQL Connector):
pip install --upgrade mysql-connector-python
Node.js:
npm install mysql2@latest
PHP (MySQLi / PDO):
sudo apt update && sudo apt install php-mysql

Check Firewall and MySQL Port

If MySQL denies access, a firewall might be blocking port 3306. I check with:

sudo ufw status

If it's blocking MySQL, I allow it:

sudo ufw allow 3306/tcp

For iptables, I add:

sudo iptables -A INPUT -p tcp --dport 3306 -j ACCEPT

I also verify MySQL listens on port 3306:

sudo netstat -tulnp | grep mysql

Restart Services and Test the Connection

Once I make changes, I restart MySQL:

sudo systemctl restart mysql

Then I test the connection manually and via the application.

Final Thoughts

If I see "Access Denied for User", I:

Verify username and password.
Grant remote access if needed.
Check authentication plugin compatibility.
Update MySQL Connector.
Check firewall settings.
Restart MySQL and test the connection.

Following these steps always gets MySQL authentication working!

Fixing MySqlConnector.MySqlException (0x80004005): Access Denied for User – A Server Administrator's Guide

Verify the Correct Username and Password

Manual Authentication Test

Check Remote Access Settings

Grant Remote Access

Check MySQL Bind Address

Ensure the Correct Authentication Plugin

Ensure MySQL Connector Is Updated

Check Firewall and MySQL Port

Restart Services and Test the Connection

Final Thoughts

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Fixing MySqlConnector.MySqlException (0x80004005): Access Denied for User – A Server Administrator's Guide

Verify the Correct Username and Password

Manual Authentication Test

Check Remote Access Settings

Grant Remote Access

Check MySQL Bind Address

Ensure the Correct Authentication Plugin

Ensure MySQL Connector Is Updated

Check Firewall and MySQL Port

Restart Services and Test the Connection

Final Thoughts

Cloud Windows VDS

Hosting

Cloud Solution

For You

VDS

Website Builders

Our services

Client Area

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