Passwords can be written as plain text in SQL statements such as
SET PASSWORD. If such statements
are logged by the MySQL server as written, passwords in them
become visible to anyone with access to the logs.
Statement logging avoids writing passwords as cleartext for the following statements:
CREATE USER ... IDENTIFIED BY ... ALTER USER ... IDENTIFIED BY ... SET PASSWORD ... START SLAVE ... PASSWORD = ... START REPLICA ... PASSWORD = ... CREATE SERVER ... OPTIONS(... PASSWORD ...) ALTER SERVER ... OPTIONS(... PASSWORD ...)
Passwords in those statements are rewritten to not appear
literally in statement text written to the general query log,
slow query log, and binary log. Rewriting does not apply to
other statements. In particular,
UPDATE statements for the
mysql.user system table that refer to literal
passwords are logged as is, so you should avoid such statements.
(Direct modification of grant tables is discouraged, anyway.)
For the general query log, password rewriting can be suppressed
by starting the server with the
--log-raw option. For security
reasons, this option is not recommended for production use. For
diagnostic purposes, it may be useful to see the exact text of
statements as received by the server.
By default, contents of audit log files produced by the audit log plugin are not encrypted and may contain sensitive information, such as the text of SQL statements. For security reasons, audit log files should be written to a directory accessible only to the MySQL server and to users with a legitimate reason to view the log. See Section 18.104.22.168, “MySQL Enterprise Audit Security Considerations”.
An implication of password rewriting is that statements that
cannot be parsed (due, for example, to syntax errors) are not
written to the general query log because they cannot be known to
be password free. Use cases that require logging of all
statements including those with errors should use the
--log-raw option, bearing in mind
that this also bypasses password rewriting.
Password rewriting occurs only when plain text passwords are expected. For statements with syntax that expect a password hash value, no rewriting occurs. If a plain text password is supplied erroneously for such syntax, the password is logged as given, without rewriting.
To guard log files against unwarranted exposure, locate them in
a directory that restricts access to the server and the database
administrator. If the server logs to tables in the
mysql database, grant access to those tables
only to the database administrator.
Replicas store the password for the replication source server in
their connection metadata repository, which by default is a
table in the
mysql database named
slave_master_info. The use of a file in the
data directory for the connection metadata repository is now
deprecated, but still possible (see
Section 17.2.4, “Relay Log and Replication Metadata Repositories”). Ensure that the connection
metadata repository can be accessed only by the database
administrator. An alternative to storing the password in the
connection metadata repository is to use the
REPLICA (or before MySQL 8.0.22,
GROUP_REPLICATION statement to specify credentials for
connecting to the source.
Use a restricted access mode to protect database backups that include log tables or log files containing passwords.