LOAD DATA statement loads a
data file into a table. The statement can load a file located on
the server host, or, if the
LOCAL keyword is
specified, on the client host.
LOCAL version of
DATA has two potential security issues:
LOAD DATA LOCALis an SQL statement, parsing occurs on the server side, and transfer of the file from the client host to the server host is initiated by the MySQL server, which tells the client the file named in the statement. In theory, a patched server could tell the client program to transfer a file of the server's choosing rather than the file named in the statement. Such a server could access any file on the client host to which the client user has read access. (A patched server could in fact reply with a file-transfer request to any statement, not just
LOAD DATA LOCAL, so a more fundamental issue is that clients should not connect to untrusted servers.)
In a Web environment where the clients are connecting from a Web server, a user could use
LOAD DATA LOCALto read any files that the Web server process has read access to (assuming that a user could run any statement against the SQL server). In this environment, the client with respect to the MySQL server actually is the Web server, not a remote program being run by users who connect to the Web server.
To avoid connecting to untrusted servers, clients can establish a
secure connection and verify the server identity by connecting
and the appropriate CA certificate.
LOAD DATA issues, clients
should avoid using
LOCAL unless proper
client-side precautions have been taken.
For control over local data loading, MySQL permits the capability to be enabled or disabled. In addition, as of MySQL 8.0.21, MySQL enables clients to restrict local data loading operations to files located in a designated directory.
Adminstrators and applications can configure whether to permit local data loading as follows:
On the server side:
local_infilesystem variable controls server-side
LOCALcapability. Depending on the
local_infilesetting, the server refuses or permits local data loading by clients that request local data loading.
local_infileis disabled. To explicitly cause the server to refuse or permit
LOAD DATA LOCALstatements (regardless of how client programs and libraries are configured at build time or runtime), start mysqld with
local_infiledisabled or enabled.
local_infilecan also be set at runtime.
On the client side:
ENABLED_LOCAL_INFILECMake option controls the compiled-in default
LOCALcapability for the MySQL client library (see Section 2.9.7, “MySQL Source-Configuration Options”). Clients that make no explicit arrangements therefore have
LOCALcapability disabled or enabled according to the
ENABLED_LOCAL_INFILEsetting specified at MySQL build time.
By default, the client library in MySQL binary distributions is compiled with
ENABLED_LOCAL_INFILEdisabled. If you compile MySQL from source, configure it with
ENABLED_LOCAL_INFILEdisabled or enabled based on whether clients that make no explicit arrangements should have
LOCALcapability disabled or enabled.
For client programs that use the C API, local data loading capability is determined by the default compiled into the MySQL client library. To enable or disable it explicitly, invoke the
mysql_options()C API function to disable or enable the
MYSQL_OPT_LOCAL_INFILEoption. See mysql_options().
For the mysql client, local data loading capability is determined by the default compiled into the MySQL client library. To disable or enable it explicitly, use the
If you use
LOAD DATA LOCALin Perl scripts or other programs that read the
[client]group from option files, you can add a
local-infileoption setting to that group. To prevent problems for programs that do not understand this option, specify it using the
In all cases, successful use of a
LOCALload operation by a client also requires that the server permits local loading.
LOCAL capability is disabled, on either
the server or client side, a client that attempts to issue a
LOCAL statement receives the following error message:
ERROR 3950 (42000): Loading local data is disabled; this must be enabled on both the client and server side
As of MySQL 8.0.21, the MySQL client library enables client applications to restrict local data loading operations to files located in a designated directory. Certain MySQL client programs take advantage of this capability.
Client programs that use the C API can control which files to
permit for load data loading using the
MYSQL_OPT_LOAD_DATA_LOCAL_DIR options of the
mysql_options() C API function
The effect of
depends on whether
LOCAL data loading is
enabled or disabled:
LOCALdata loading is enabled, either by default in the MySQL client library or by explicitly enabling
MYSQL_OPT_LOAD_DATA_LOCAL_DIRoption has no effect.
LOCALdata loading is disabled, either by default in the MySQL client library or by explicitly disabling
MYSQL_OPT_LOAD_DATA_LOCAL_DIRoption can be used to designate a permitted directory for locally loaded files. In this case,
LOCALdata loading is permitted but restricted to files located in the designated directory. Interpretation of the
MYSQL_OPT_LOAD_DATA_LOCAL_DIRvalue is as follows:
If the value is the null pointer (the default), it names no directory, with the result that no files are permitted for
If the value is a directory path name,
LOCALdata loading is permitted but restricted to files located in the named directory. Comparison of the directory path name and the path name of files to be loaded is case-sensitive regardless of the case sensitivity of the underlying file system.
MySQL client programs use the preceding
mysql_options() options as
The mysql client has a
--load-data-local-diroption that takes a directory path or an empty string. mysql uses the option value to set the
MYSQL_OPT_LOAD_DATA_LOCAL_DIRoption (with an empty string setting the value to the null pointer). The effect of
--load-data-local-dirdepends on whether
LOCALdata loading is enabled:
--load-data-local-dirapplies, the option value designates the directory in which local data files must be located. Comparison of the directory path name and the path name of files to be loaded is case-sensitive regardless of the case sensitivity of the underlying file system. If the option value is the empty string, it names no directory, with the result that no files are permitted for local data loading.
MYSQL_OPT_LOAD_DATA_LOCAL_DIRfor each file that it processes so that the directory containing the file is the permitted local loading directory.
For data loading operations corresponding to
LOAD DATAstatements, mysqlbinlog extracts the files from the binary log events, writes them as temporary ffiles to the local file system, and writes
LOAD DATA LOCALstatements to cause the files to be loaded. By default, mysqlbinlog writes these temporary files to an operating system-specific directory. The
--local-loadoption can be used to explicitly specify the directory where mysqlbinlog should prepare local temporary files.
Because other processes can write files to the default system-specific directory, it is advisable to specify the
--local-loadoption to mysqlbinlog to designate a different directory for data files, and then designate that same directory by specifying the
--load-data-local-diroption to mysql when processing the output from mysqlbinlog.