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If i have a php file which is receiving a $_GET['value'] is it safe from sql injection or code-injection for me to start my php file with
if (in_array($_GET['value'], $allowed_values);)
{ /* normal page code handling the $_GET['value'] */
} else { unset($_GET['name'])
}
$allowed values is obviously an array of all values which i am expecting as safe for $_Get['value']. Is this still unsafe? Thank you.
Yes, that's a common and safe technique that can be used in situations where query parameters can't be used. For instance, if the value will be used as a table or column name, you can't provide it as a query parameter, you have to substitute it directly into the SQL string. Whitelisting like this is the recommended way to ensure that this is safe.
It depends on the values in the $allowed_values array, and how you are interpolating the value into your SQL query.
For example:
$allowed_values = [ 'a word' ];
if (in_array($_GET['value'], $allowed_values)) {
$sql = "SELECT * FROM mytable WHERE id = {$_GET['value']};";
}
Definitely not safe. It results in the SQL:
SELECT * FROM mytable WHERE id = a word;
This is a syntax error.
Why would you not just use SQL query parameters? Then you don't need to worry if it's safe or not. Query parameters separate the values from the SQL parsing, so there's no way any kind of value can cause SQL injection.
You won't have to have an $allowed_values array. You won't have to remember to check if the GET input is in the array. You won't have to worry about quoting or escaping.
It's true that query parameters only work for values, that is in place of a quoted string literal or quoted datetime literal or numeric literal. If you need other parts of your query to be dynamic, like the table name or column name or SQL keywords, etc. then use an allow-list solution like you are showing.
But the more common case of interpolating dynamic values is better handled by query parameters:
$sql = "SELECT * FROM mytable WHERE id = ?";
$stmt = $pdo->prepare($sql);
$stmt-execute( [ $_GET['value'] ] );
let's discuss this thing in little details:
Your code is like this :
if (in_array($_GET['value'], $allowed_values);) {
...........
$sql = "SELECT * FROM mytable WHERE id = $_GET['value']";
...........
}
else {
unset($_GET['name'])
}
now let's assume, you have some values :
the in_array() function will allow only some pre-defined values, you couldn't have the option to take custom user input by $_GET, but as only pre-defined values are allowed,any SQL command will be safe inside if statement.
now take this example of $allowed_values array :
$allowed_values = ['some details' , 'another details' ,3, ' 105; DROP TABLE mytable;', 22 , 'ok'];
If any of these array values have a string that can have potential SQL injection capability, then there will be an issue. but I think you will not put any such string in the array $allowed_values. ( in this above-mentioned example, index 3, ' 105; DROP TABLE mytable;' can delete the table mytable ). else the SQL command will be safe.
now you can add an extra layer of safety in the code, by using PDO for any SQL query. (in this example you do not need that, as in_array() function is 100% safe unless you yourself put any malicious code in the array, as per my above-mentioned example). but for other types of user input where you have to do some SQL query depend on the user input, you can use PDO -prepared statement.
a PDO example is this :
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDBPDO";
$conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
// set the PDO error mode to exception
$conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$stmt = $conn->prepare("INSERT INTO photos (username, kname) VALUES (?, ?)");
$stmt->execute([ $username , $kname ]);
For more info, try w3school link: https://www.w3schools.com/php/php_mysql_prepared_statements.asp
So I'm making my own blog scripts using MYSQL and PHP.
I had the whole 'writing the blog to a database' thing working perfectly, until I realised that if you tried to write a blog with speech marks, this would prevent the INSERT statement from working (obviously - the speechmarks were ending the SQL statement).
So I tried to use real_escape_string, and now the INSERT doesn't work even if you exclude quotes.
I tried using:
sqlstate
in order to find out the issue, and it returned "42000" - which, after googling for a little bit, refers to a syntax error, which doesn't make much sense as there is no syntax error before the use of real_escape_string.
Also, I'm now getting this error:
Call to a member function close() on a non-object in /postarticle.php on line 37
Which refers to the close() call in the ELSE statement.
Please may you help? Been going round in circles for a while. Here is my code:
<?php
$host = 'CENSORED';
$user = 'CENSORED';
$pass = 'CENSORED';
$db = 'CENSORED';
$connection = new mysqli($host,$user,$pass,$db);
$_SESSION["article"] = $_POST["article"];
$date_of_blog = getdate();
$article = ($_SESSION["article"]);
$sql1 = "SELECT * FROM `Blogs`";
$res1 = $connection->query($sql1);
$newrows = $res1->num_rows + 1;
$sql2 = "INSERT INTO Blogs(BlogID, Blog_Contents, D_O_B) VALUES ('$newrows','$article','$date_of_blog')";
$sql2 = $connection->real_escape_string($sql2);
$res2 = $connection->query($sql2);
if ($res2->num_rows == $newrows)
{
$res->close();
$connection->close();
header( 'Location: adminpanel.php' );
}
else
{
echo ($connection->sqlstate);
$connection->close();
$res->close();
}
exit();
?>
Also, on a side note, the getdate() call that I've got has never worked. In the database every blog post comes up as:
0000:00:00 00:00:00
EDIT:
Issue is now solved. Find the functional code below:
<?php
$host = 'CENSORED';
$user = 'CENSORED';
$pass = 'CENSORED';
$db = 'CENSORED';
$connection = new mysqli($host,$user,$pass,$db);
$_SESSION["article"] = $_POST["article"];
$article = ($_SESSION["article"]);
$article = $connection->real_escape_string($article);
$sql1 = "SELECT * FROM `Blogs`";
$res1 = $connection->query($sql1);
$newrows = $res1->num_rows + 1;
$sql2 = "INSERT INTO Blogs(BlogID, Blog_Contents, D_O_B) VALUES (\"$newrows\",\"$article\",CURDATE())";
$res2 = $connection->query($sql2);
if ($res2 != false)
{
header( 'Location: adminpanel.php' );
}
else
{
echo ($connection->sqlstate);
}
$connection->close();
$res->close();
exit();
?>
I'm very sorry if these questions are basic and annoy the professionals around here; I've tried to follow the guidelines and I've googled for a while etc. I just haven't found any solutions that match my issue(s).
Thankyou for your time.
There are a number issues with the code as originally posted. Chiefly, the cause of the two issues you initially identified is a misuse of mysqli::real_escape_string(). It needs to be called on each variable individually which appears in the code. So instead of calling it on the whole statement, it must be called multiple times for multiple variables like:
$article = $connection->real_escape_string($connection);
The failure of the query due to incorrect quoting (due to real_escape_string()) is the reason for the error message calling close().
As ascertained in the comments, you are using num_rows + 1 to validate that one new row has been inserted based on the previous number of rows returned. This is problematic for a few reasons. Mainly, it exposes a race condition wherein a row may be inserted from two sessions at once and one or both will fail because the expected value for $newrows doesn't match. Really BlogID should be an auto_increment column in your database. That eliminates the need for any logic around it whatsoever. You don't even need to include it in the INSERT because it will be automatically incremented.
That also completely eliminates the need for the first SELECT statement.
Substituting MySQL's native NOW() function for the date value, you can simplify the statement to:
INSERT INTO Blogs (Blog_Contents, D_O_B) VALUES ('$article', NOW())
To test success or failure of the insert, you just need to verify that its variable is not false.
Putting this together, your code can be reduced as:
if (!isset($_POST['article'])) {
// exit or handle an empty post somehow...
}
$connection = new mysqli($host,$user,$pass,$db);
$_SESSION["article"] = $_POST["article"];
// Escape $article for later use
$article = $connection->real_escape_string($_SESSION["article"]);
// Only an INSERT is needed. $article is already escaped
$sql = "INSERT INTO Blogs (Blog_Contents, D_O_B) VALUES ('$article', NOW())";
// Run the query
$res = $connection->query($sql);
// Test for failure by checking for a false value
if ($res) {
// The connection & resource closure can be omitted
// PHP will handle that automatically and implicitly.
header( 'Location: adminpanel.php' );
// Explictly exit as good practice after redirection
exit();
}
else {
// The INSERT failed. Check the error message
echo $connection->error;
}
This should bring your current code into working order. However, since you're learning this it is an excellent time to begin learning to use prepared statements via prepare()/bind_param()/execute() in MySQLi. This is a recommended best practice to prevent SQL injection, although using real_escape_string() works as long as you use it correctly and never forget.
See How can I prevent SQL injection in PHP for examples.
But it would look like:
// connection already established, etc...
// Prepare the statement using a ? placeholder for article
$stmt = $connection->prepare("INSERT INTO Blogs (Blog_Contents, D_O_B) VALUES (?, NOW())");
if ($stmt) {
// bind in the variable and execute
// Note that real_escape_string() is not needed when using
// the ? placeholder for article
$stmt->bind_param('s', $_SESSION['article']);
$stmt->execute();
// Redirect
header( 'Location: adminpanel.php' );
exit();
}
else {
echo $connection->error;
}
You need to apply the real_escape_string function to the variables not the entire SQL string.
$sql2 = "INSERT INTO Blogs(BlogID, Blog_Contents, D_O_B) VALUES ('".$connection->real_escape_string($newrows)."','".$connection->real_escape_string($article)."','".$connection->real_escape_string($date_of_blog)."')";
The purpose is to remove anything that might be misinterpreted as query functions by MySQL, but there are parts of the query that you obviously want to be interpreted as such.
So in this program I'm writing, I actually grab a SQL query from the user using a form. I then go on to run that query on my database.
I know not to "trust" user input, so I want to do sanitization on the input. I'm trying to use mysql_real_escape_string but have been unsuccessful in getting it to work.
Here's what I'm trying, given the input:
select * from Actor;
//"query" is the input string:
$clean_string = mysql_real_escape_string($query, $db_connection);
$rs = mysql_query($clean_string, $db_connection);
if (!$rs)
{
echo "Invalid input!";
}
This is ALWAYS giving me the
"Invalid input!"
error.
When I take out the clean_string part and just run mysql_query on query, the
"invalid
input"
message is not output. Rather, when I do this:
$rs = mysql_query($query, $db_connection);
if (!$rs)
{
echo "Invalid input!";
}
It does NOT output
"invalid input".
However, I need to use the mysql_real_escape_string function. What am I doing wrong?
Update:
Given
select * from Actor; as an input, I've found the following.
Using echo statements I've
found that before sanitizing, the string holds the value:
select * from Actor;
which is correct. However, after sanitizing it holds the incorrect
value of select *\r\nfrom Actor;, hence the error message. Why is
mysql_real_escape_string doing this?
use it on the actual values in your query, not the whole query string itself.
example:
$username = mysql_real_escape_string($_POST['username']);
$query = "update table set username='$username' ...";
$rs = mysql_query($query);
Rather than using the outdated mysql extension, switch to PDO. Prepared statement parameters aren't vulnerable to injection because they keep values separate from statements. Prepared statements and PDO have other advantages, including performance, ease of use and additional features. If you need a tutorial, try "Writing MySQL Scripts with PHP and PDO".
mysql_real_escape_string() is the string escaping function. It does not make any input safe, just string values, not for use with LIKE clauses, and integers need to be handled differently still.
An easier and more universal example might be:
$post = array_map("mysql_real_escape_string", $_POST);
// cleans all input variables at once
mysql_query("SELECT * FROM tbl WHERE id='$post[id]'
OR name='$post[name]' OR mtime<'$post[mtime]' ");
// uses escaped $post rather than the raw $_POST variables
Note how each variable must still be enclosed by ' single quotes for SQL strings. (Otherwise the escaping would be pointless.)
You should use mysql_real_escape_string to escape the parameters to the query, not the entire query itself.
For example, let's say you have two variables you received from a form. Then, your code would look like this:
$Query = sprintf(
'INSERT INTO SomeTable VALUES("%s", "%s")',
mysql_real_escape_string($_POST['a'], $DBConnection),
mysql_real_escape_string($_POST['b'], $DBConnection)
);
$Result = mysql_query($Query, $DBConnection);
manual mysql_real_escape_string()
Escapes special characters in a string
for use in an SQL statement
So you can't escape entire query, just data... because it will escape all unsafe characters like quotes (valid parts of query).
If you try something like that (to escape entire query)
echo mysql_real_escape_string("INSERT INTO some_table VALUES ('xyz', 'abc', '123');");
Output is
INSERT INTO some_table VALUES (\'xyz\',
\'abc\', \'123\');
and that is not valid query any more.
This worked for me. dwolf (wtec.co)
<?php
// add data to db
require_once('../admin/connect.php');
$mysqli = new mysqli($servername, $username, $password, $dbname);
/* check connection */
if (mysqli_connect_errno()) {
printf("Connect failed: %s\n", mysqli_connect_error());
exit();
}
$post = $mysqli->real_escape_string($_POST['name']);
$title = $mysqli->real_escape_string($_POST['message']);
/* this query with escaped $post,$title will work */
if ($mysqli->query("INSERT into press (title, post) VALUES ('$post', '$title')")) {
printf("%d Row inserted.\n", $mysqli->affected_rows);
}
$mysqli->close();
//header("location:../admin");
?>
So in this program I'm writing, I actually grab a SQL query from the user using a form. I then go on to run that query on my database.
I know not to "trust" user input, so I want to do sanitization on the input. I'm trying to use mysql_real_escape_string but have been unsuccessful in getting it to work.
Here's what I'm trying, given the input:
select * from Actor;
//"query" is the input string:
$clean_string = mysql_real_escape_string($query, $db_connection);
$rs = mysql_query($clean_string, $db_connection);
if (!$rs)
{
echo "Invalid input!";
}
This is ALWAYS giving me the
"Invalid input!"
error.
When I take out the clean_string part and just run mysql_query on query, the
"invalid
input"
message is not output. Rather, when I do this:
$rs = mysql_query($query, $db_connection);
if (!$rs)
{
echo "Invalid input!";
}
It does NOT output
"invalid input".
However, I need to use the mysql_real_escape_string function. What am I doing wrong?
Update:
Given
select * from Actor; as an input, I've found the following.
Using echo statements I've
found that before sanitizing, the string holds the value:
select * from Actor;
which is correct. However, after sanitizing it holds the incorrect
value of select *\r\nfrom Actor;, hence the error message. Why is
mysql_real_escape_string doing this?
use it on the actual values in your query, not the whole query string itself.
example:
$username = mysql_real_escape_string($_POST['username']);
$query = "update table set username='$username' ...";
$rs = mysql_query($query);
Rather than using the outdated mysql extension, switch to PDO. Prepared statement parameters aren't vulnerable to injection because they keep values separate from statements. Prepared statements and PDO have other advantages, including performance, ease of use and additional features. If you need a tutorial, try "Writing MySQL Scripts with PHP and PDO".
mysql_real_escape_string() is the string escaping function. It does not make any input safe, just string values, not for use with LIKE clauses, and integers need to be handled differently still.
An easier and more universal example might be:
$post = array_map("mysql_real_escape_string", $_POST);
// cleans all input variables at once
mysql_query("SELECT * FROM tbl WHERE id='$post[id]'
OR name='$post[name]' OR mtime<'$post[mtime]' ");
// uses escaped $post rather than the raw $_POST variables
Note how each variable must still be enclosed by ' single quotes for SQL strings. (Otherwise the escaping would be pointless.)
You should use mysql_real_escape_string to escape the parameters to the query, not the entire query itself.
For example, let's say you have two variables you received from a form. Then, your code would look like this:
$Query = sprintf(
'INSERT INTO SomeTable VALUES("%s", "%s")',
mysql_real_escape_string($_POST['a'], $DBConnection),
mysql_real_escape_string($_POST['b'], $DBConnection)
);
$Result = mysql_query($Query, $DBConnection);
manual mysql_real_escape_string()
Escapes special characters in a string
for use in an SQL statement
So you can't escape entire query, just data... because it will escape all unsafe characters like quotes (valid parts of query).
If you try something like that (to escape entire query)
echo mysql_real_escape_string("INSERT INTO some_table VALUES ('xyz', 'abc', '123');");
Output is
INSERT INTO some_table VALUES (\'xyz\',
\'abc\', \'123\');
and that is not valid query any more.
This worked for me. dwolf (wtec.co)
<?php
// add data to db
require_once('../admin/connect.php');
$mysqli = new mysqli($servername, $username, $password, $dbname);
/* check connection */
if (mysqli_connect_errno()) {
printf("Connect failed: %s\n", mysqli_connect_error());
exit();
}
$post = $mysqli->real_escape_string($_POST['name']);
$title = $mysqli->real_escape_string($_POST['message']);
/* this query with escaped $post,$title will work */
if ($mysqli->query("INSERT into press (title, post) VALUES ('$post', '$title')")) {
printf("%d Row inserted.\n", $mysqli->affected_rows);
}
$mysqli->close();
//header("location:../admin");
?>
I am trying to insert values in database and values are not being inserted, here is the code i have:
$user_name = "username";
$password = "password";
$database = "database";
$server = "localhost";
$db_handle = mysql_connect($server, $user_name, $password);
$db_found = mysql_select_db($database, $db_handle);
if ($db_found) {
$SQL = 'INSERT INTO table (anInt, DomainName, URL, Rank, PageRank, Google, Bing, Boss, IndexedPage, Backlinks) VALUES ($anInt, $Domain, $URL, $Rank, $Pagerank, $Google, $Bing, $Yahoo, $Pages, $backlinks)';
$result = mysql_query($SQL);
mysql_close($db_handle);
print "Records added to the database";
it is printing that records added to the database but when looking at the database nothing is being added. some of the values are doubles, text, and ints. Is there anyway to debug this? I will be adding more information to the post if someone asks me to.
and of course I have an else statement i just thought it is not relevant since it is telling me that records are added.
First of all, you should escape the string values you are passing into the SQL query, using mysql_real_escape_string.
Then, you should add quotes, in your SQL query, arround the fields that are meant to contain strings.
I don't really know which fields are integers and which fields are strings, but you should be using something like this to build your SQL query :
// Escape the string data, and make sure integer really contain integers
$anInt = intval($anInt);
$Domain = mysql_real_escape_string($Domain);
$URL = mysql_real_escape_string($URL);
$Rank = intval($Rank);
$Pagerank = = intval($Pagerank);
$Google = intval($Google);
$Bing = intval($Bing);
$Yahoo = intval($Yahoo);
$Pages = intval($Pages);
$backlinks = intval($backlinks );
// Build the SQL query, using the "safe" variables
$SQL = 'INSERT INTO table (anInt, DomainName, URL, Rank, PageRank, Google, Bing, Boss, IndexedPage, Backlinks)
VALUES ($anInt, '$Domain', '$URL', $Rank, $Pagerank, $Google, $Bing, $Yahoo, $Pages, $backlinks)';
This is supposing that only DomainName and URL are meant to contain strings -- you might have to use mysql_real_escape_string and add quotes arround the values for some other fields too, if needed.
Then, you should take a look at the return value of mysql_query : for an insert query, in case of an error, it'll return false.
Here, if your $result variable is false, you should use mysql_error and mysql_errno : they'll allow you to know what error happened -- it will help detecting errors in your SQL query, for instance.
If this doesn't solve the problem, you should try outputting the SQL query, and run it using something like phpMyAdmin, to make sure it's OK.
I am no PHP expert, but I have 2 remarks.
You don't check the error (perhaps with mysql_errno()) so you don't know whether the records were added
I think the values, if they are strings, should be given like
'$Domain'
that is, escaped with ' characters.
better would be, of course, using something like
$sql = sprintf("INSERT ... VALUES(%d, '%s', '%s',...)",
$anInt, mysql_real_escape_string($Domain), ...);
if you insert user-supplied input.
You could examine the $result:
$result = mysql_query($query);
if (!$result) {
print "An error occured: " . mysql_error() . "\n";
}
My guess is that you're passing a string without quotes, like:
VALUES (Hello)
where you should pass it like:
VALUES ('Hello')
Like the commenter said, if the user can control these strings, you are open to an SQL Injection attack. You can prevent that attack by escaping the strings, for example:
$query = sprintf("INSERT INTO table (DomainName) VALUES ('%s')",
mysql_real_escape_string($domain_name));
In SQL queries, you need to enquote strings correctly, or it will produce an error. So all your variables that are used to store non-int or non-boolean values in the database need quotes around the values.
Additionally you should make sure that SQL injections are not a problem by escaping all values with mysql_real_escape_string first.
Apart from sql injections your error handling is not complete...
if (!$db_found) {
echo "datbase not found.";
}
else {
$SQL = 'INSERT INTO
table
(...)
VALUES
(...)
';
$result = mysql_query($SQL, $db_handle);
if ( !$result ) {
echo "error: ", mysql_error($db_handle);
}
else {
print "Records added to the database";
}
}
mysql_close($db_handle);
In case a query causes an error mysql_query() return FALSE and mysql_error() will tell you more about the error.
Well there are security issues with the code but to address one problem
you are not enclosing your string values in quotes in the SQL statement.
First of all, please regard everybody else's advice on safe database handling and avoiding injection.
The reason your query isn't doing anything is probably that you enclosed the string in single quotes. In PHP single quotes enforce the string to be literal. Unlike when using double quotes, variables will NOT be substituted. So '$foo' represents the sequence of characters '$'.'f'.'o'.'o'. "$foo" on the other hand represents the sequence of characters of whatever the variable $foo contains at the time of the string's definition.
You can use mysql_error() to catch most problems with MySQL. Even if the message isn't helping you, you at least know whether the query was parsed properly, i.e. on which end of the connection the problem lies.