Fixing MySqlConnector.MySqlException (0x80004005): Access Denied for User

Verify the Correct Username and Password

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

For other MySQL/MariaDB access topics, see MySQL Error #1227 — SUPER Privilege Required, MySQL native_password Access Denied, and MySql.Data 0x80004005 (.NET classic).

SELECT user, host FROM mysql.user;

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

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

Check Remote Access Settings

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

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

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

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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

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