I am using jdbc PreparedStatement for data insertion.
Statement stmt = conn.prepareStatement(
"INESRT INTO" + tablename+ "("+columnString+") VALUES (?,?,?)");
tablename and columnString are something that is dynamically generated.
I've tried to parameterise tablename and columnString but they will just resolve to something like 'tablename' which will violate the syntax.
I've found somewhere online that suggest me to lookup the database to check for valid tablename/columnString, and cache it somewhere(a Hashset perhaps) for another query, but I'm looking for better performance/ quick hack that will solve the issue, perhaps a string validator/ regex that will do the trick.
Have anyone came across this issue and how do you solve it?
I am not a java-guy, so, only a theory.
You can either format dynamically added identifiers or white-list them.
Second option is way better. Because
most developers aren't familiar enough with identifiers to format them correctly. Say, to quote an identifier, which is offered in the first comment, won't make it protected at all.
there could be another attack vector, not entirely an injection, but similar: imagine there is a column in your table, an ordinary user isn't allowed to - say, called "admin". With dynamically built columnString using data coming from the client side, it's piece of cake to forge a privilege escalation.
Thus, to list all the possible (and allowed) variants in your code beforehand, and then to verify entered value against it, would be the best.
As of columnString - is consists of separate column names. Thus, to protect it, one have to verify each separate column name against a white list, and then assemble a final columnString from them.
Create a method that generates the sql string for you:
private static final String template = "insert into %s (%s) values (%s)";
private String buildStmt(String tblName, String ... colNames) {
StringJoiner colNamesJoiner = new StringJoiner(",");
StringJoiner paramsJoiner = new StringJoiner(",");
Arrays.stream(colNames).forEach(colName -> {
colNamesJoiner.add(colName);
paramsJoiner.add("?");
});
return String.format(template, tblName, colNamesJoiner.toString(), paramsJoiner.toString());
}
Then use it...
Statement stmt = conn.prepareStatement(buildStmt(tablename, [your column names]));
As an elaboration on #Anders' answer, don't use the input parameter as the name directly, but keep a properties file (or database table) that maps a set of allowed inputs to actual table names.
That way any invalid name will not lead to valid SQL (and can be caught before any SQL is generated) AND the actual names are never known outside the application, thus making it far harder to guess what would be valid SQL statements.
I think, the best approach is to get table and columns names from database or other non user input, and use parameters in prepared statement for the rest.
There are multiple solutions we can apply.
1) White List Input Validation
String tableName;
switch(PARAM):
case "Value1": tableName = "fooTable";
break;
case "Value2": tableName = "barTable";
break;
...
default : throw new InputValidationException("unexpected value provided for table name");
By doing this input validation on tableName, will allows only specified tables in the query, so it will prevents sql injection attack.
2) Bind your dynamic columnName(s) or tableName(s) with special characters as shown below
eg:
For Mysql : use back codes (`)
Select `columnName ` from `tableName `;
For MSSQL : Use double codes(" or [ ] )
select "columnName" from "tableName"; or
select [columnName] from [tableName];
Note: Before doing this you should sanitize your data with this special characters ( `, " , [ , ] )
Related
I have a requirement. The technology is quite old doesn't support spring at all . It is pure java application with jdbc connection.
Requirement is :
Suppose
select * from employee where empid = <<empid>> and designation = 'Doctor'
I am trying to replace <> with actual int value in java . How I can do it ?
String query = "select * from employee where empid = <<empid>> and designation = 'Doctor'";
if(query.contains("<<empid>>"))
/// Here I want to replace <<empid>> with actual int value in java
Any leads will be helpful
The code you didn't paste, that actually executes the SQL is either [A] a massive security leak that needs serious rewrites, or [B] is using PreparedStatement.
Here's the problem: SQL injection. Creating the SQL string by mixing a template or a bunch of string constants together with a bunch of user input is a security leak. For example, if you try to make SELECT * FROM users WHERE email = 'foo#bar.com' by e.g. String sql = "SELECT * FROM users WHERE email = '" + email + "'";, the problem is, what if the user puts in the web form, in the 'email' field: whatever#foo.com'; DROP TABLE users CASCADE; EXEC 'FORMAT C: /y /force'; --? Then the SQL becomes:
SELECT * FROM users WHERE email = 'whatever#foo.com'; DROP TABLE users CASCADE; EXEC 'FORMAT C: /y /force'; --';
That is legal SQL and you really, really, really don't want your DB engine to execute it.
Each DB engine has its own ideas on what's actually legal, and may do crazy things such as treating curly quotes as real quotes, etc. So, there is no feasible blacklist or whitelist technology you can think of that will properly cover all the bases: You need to ask your DB engine to do this for you, you can't fix this hole yourself.
Java supports this, via java.sql.PreparedStatement. You instead always pass a fully constant SQL string to the engine, and then fill in the blanks, so to speak:
PreparedStatement ps = con.prepareStatement("SELECT * FROM users WHERE email = ?");
ps.setString(1, "foo#whatever.com");
ps.query();
That's how you do it (and add try-with-resources just like you should already be doing here; statements and resultsets are resources you must always close). Even if you call .setString(1, "foo#whatever.com'; DROP TABLE users CASCADE; --"), then it'll simply look for a row in the database that has that mouthful in the email field. It will not delete the entire users table. Security hole eliminated (and this is the only feasible way to eliminate it).
So, check out that code. Is it using preparedstatement? In that case, well, one way or another that code needs to be calling:
ps.setInt(1, 999);
Where ps is the PreparedStatement object created with connection.prepareStatement(...) where ... is either an SQL constant or at least your input string where the <<empid>> was replaced with a question mark and never with any string input from an untrusted source. The 1 in ps.setInt(1, 999) is the position of the question mark (1 = the first question becomes 999), and the 999 is your actual number. It may look like:
if (input instanceof String) {
ps.setString(idx++, (String) input);
} else if (input instanceof Integer) {
ps.setInt(idx++, ((Integer) input).intValue());
} ...
etcetera. If you don't see that, find the setInt invoke and figure out how to get there. If you don't see any setInt, then what you want is not possible without making some updates to this code.
If you don't even see PreparedStatement anywhere in the code, oh dear! Take that server offline right now, research if a security leak has occurred, if this server stored european data you have 72 hours to notify all users if it has or you can't reasonably figure out e.g. by inspecting logs that it hasn't, or you're in breach of the GDPR. Then rewrite that part using PreparedStatement to solve the problem.
I was wondering if there was any way to specify returned column names using prepared statements.
I am using MySQL and Java.
When I try it:
String columnNames="d,e,f"; //Actually from the user...
String name = "some_table"; //From user...
String query = "SELECT a,b,c,? FROM " + name + " WHERE d=?";//...
stmt = conn.prepareStatement(query);
stmt.setString(1, columnNames);
stmt.setString(2, "x");
I get this type of statement (printing right before execution).
SELECT a,b,c,'d,e,f' FROM some_table WHERE d='x'
I would, however, like to see:
SELECT a,b,c,d,e,f FROM some_table WHERE d='x'
I know that I cannot do this for table names, as discussed
here, but was wondering if there was some way to do it for column names.
If there is not, then I will just have to try and make sure that I sanitize the input so it doesn't lead to SQL injection vulnerabilities.
This indicates a bad DB design. The user shouldn't need to know about the column names. Create a real DB column which holds those "column names" and store the data along it instead.
And any way, no, you cannot set column names as PreparedStatement values. You can only set column values as PreparedStatement values
If you'd like to continue in this direction, you need to sanitize the column names (to avoid SQL Injection) and concatenate/build the SQL string yourself. Quote the separate column names and use String#replace() to escape the same quote inside the column name.
Prepare a whitelist of allowed column names. Use the 'query' to look up in the whitelist to see if the column name is there. If not, reject the query.
For MySQL prepared statements with NodeJS (mysqljs/mysql), what you need to know is that ? is for values, but if you need to escape column names, table names etc, use ?? instead.
Something like this will work:
SELECT ??, ??, ?? FROM ?? WHERE ?? < ?
Set values to ['id', 'name', 'address', 'user', 'id', 100]
I think this case can't work because the whole point of the prepared statement is to prevent the user from putting in unescaped query bits - so you're always going to have the text quoted or escaped.
You'll need to sanitize this input in Java if you want to affect the query structure safely.
Use sql injection disadvantage of Statement Interface as advantage.
Ex:
st=conn.createStatement();
String columnName="name";
rs=st.executeQuery("select "+ columnName+" from ad_org ");
public void MethodName(String strFieldName1, String strFieldName2, String strTableName)
{
//Code to connect with database
String strSQLQuery=String.format("select %s, %s from %s", strFieldName, strFieldName2, strTableName);
st=conn.createStatement();
rs=st.executeQuery(strSQLQuery);
//rest code
}
Below is the solution in java.
String strSelectString = String.format("select %s, %s from %s", strFieldName, strFieldName2, strTableName);
I have a problem - I create my SQL queries dynamically and basing on user input options. So the user has 5 parameters (actually it's more) and he can choose to use some of them (all if he wants) or none and specify their value in the query. So I construct my query String (basic the WHERE conditions) by checking if a parameter was selected and if a value was provided. However now there is the problem of special characters like '. I could try to use replaceAll("'", "\\") but this is quite dull and I know that preparedStatement.setString() does the job better. However for me I would need than to check again if the parameter was provided and if the previous one were also (to specify the poison of ? and connect it to the right parameter). This causes a lot of combinations and does not look elegant.
So my question is - can I somehow receive the string preparedStatement.setString() produces? Or is there a similar function that would do the same job and give me the String so I can put it in the query manually.
Maybe the intro was too long but someone might have a better idea and I wanted to explain why I need it.
What you can do is construct the basic, unparameterized SQL query based on whether the parameters were specified, and then use the prepared statement to fill in the parameters.
It could look something like this (rough sketch):
Map<String, Object> parameterValues = /*from user*/;
List<String> parameterNames = Arrays.asList("field1", "field2", "field3");
List<Object> valueList = new ArrayList<Object>();
StringBuilder statementBuilder = new StringBuilder("select * from table where ");
for ( String parameterName : parameterNames ) {
if ( parameterValues.containsKey(parameterName) ) {
statementBuilder.append(parameterName + " = ? AND");
valueList.add(parameterValues.get(parameterName));
}
}
PreparedStatement st = conn.prepareStatement(statementBuilder.toString(),
valueList);
//set each parameter here.
It's only hard the first time; then you can make it generic. That said there are probably query builders that abstract all of this away for you. I use QueryDSL but that does not have bindings for pure JDBC but rather JPA and JDO, etc.
On another forum I was given a different, simpler and cleaner approach that work perfectly.
Here are some links for others with the same problem:
http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:1669972300346534908
http://www.akadia.com/services/dyn_modify_where_clause.html
I am trying to build a dynamic sql query in java (shown below)
sqlStr = "Select * " +
"from " + tableName
if(tableName!=null){
if(tableName.equals("Table1"){
sqlStr = sqlStr.concat("order by city desc");
}else if(tableName.equals("Table2"){
sqlStr = sqlStr.concat("order by country desc");
}else if(tableName.equals("Table3"){
sqlStr = sqlStr.concat("order by price desc");
}
}
Now what i would like to do is to add a final 'else' statement which would order the query based on whether the table contains a column named 'custID'. There will be several tables with that column so i want to sort the ones that have that column by custID. (Rather than having hundreds of additional if statements for each table that does have that column name.) Is this possible? i have seen people using the 'decode' function but i cant work out how to use it here.
Use DatabaseMetaData to get the table information.
You can use the getTablexxx() and getColumnxx() methods to get the table information.
Connection conn = DriverManager.getConnection(.....);
DatabaseMetaData dbmd = conn.getMetaData();
dbmd.getxxxx();
Note: you forgot space in your code before ORDER BY clause.
If you are happy with hardcoding things, a way to avoid multiple conditionals would be to store a list of all the tables that include custID.
private final static String tablesWithCustID = "/TableX/TableY/TableZ/";
...
if (tablesWithCustID.contains( tableName )) {
sqlStr = sqlStr.concat("order by custID")
}
You could use a List instead of a simple delimited string if you like.
Perhaps better, you could store a map with table names as the key, and the sort string as the value. Load it up once, then you don't need any conditional at all.
The most straight-forward way to do it is to read the column definitions from USER_TAB_COLUMNS or ALL_TAB_COLUMNS and check for the existence of a custID column. Without crazy PL/SQL tricks, you won't be able to solve this in SQL alone.
BTW, there is a " " missing between tableName and the order by clauses.
I understand that you're looking for a solution that can do this in one query, i.e. without running a separate metadata query beforehand.
Unfortunately, this won't be possible. The decode function can do some dynamic things with column values, but not with column name. And you're looking for a solution dynamically derive the column name.
An alternative might be to just add ORDER BY 1, 2. This is an old syntax that means order by the first and than by the second column. It might be a good solution if the custID column is the first column. Otherwise it at least gives you some sorting.
How about ArrayList.contains()?
You can create a list of tables which have that column, and just check for tables.contains(tablename) in the final if condition.
I was wondering if there was any way to specify returned column names using prepared statements.
I am using MySQL and Java.
When I try it:
String columnNames="d,e,f"; //Actually from the user...
String name = "some_table"; //From user...
String query = "SELECT a,b,c,? FROM " + name + " WHERE d=?";//...
stmt = conn.prepareStatement(query);
stmt.setString(1, columnNames);
stmt.setString(2, "x");
I get this type of statement (printing right before execution).
SELECT a,b,c,'d,e,f' FROM some_table WHERE d='x'
I would, however, like to see:
SELECT a,b,c,d,e,f FROM some_table WHERE d='x'
I know that I cannot do this for table names, as discussed
here, but was wondering if there was some way to do it for column names.
If there is not, then I will just have to try and make sure that I sanitize the input so it doesn't lead to SQL injection vulnerabilities.
This indicates a bad DB design. The user shouldn't need to know about the column names. Create a real DB column which holds those "column names" and store the data along it instead.
And any way, no, you cannot set column names as PreparedStatement values. You can only set column values as PreparedStatement values
If you'd like to continue in this direction, you need to sanitize the column names (to avoid SQL Injection) and concatenate/build the SQL string yourself. Quote the separate column names and use String#replace() to escape the same quote inside the column name.
Prepare a whitelist of allowed column names. Use the 'query' to look up in the whitelist to see if the column name is there. If not, reject the query.
For MySQL prepared statements with NodeJS (mysqljs/mysql), what you need to know is that ? is for values, but if you need to escape column names, table names etc, use ?? instead.
Something like this will work:
SELECT ??, ??, ?? FROM ?? WHERE ?? < ?
Set values to ['id', 'name', 'address', 'user', 'id', 100]
I think this case can't work because the whole point of the prepared statement is to prevent the user from putting in unescaped query bits - so you're always going to have the text quoted or escaped.
You'll need to sanitize this input in Java if you want to affect the query structure safely.
Use sql injection disadvantage of Statement Interface as advantage.
Ex:
st=conn.createStatement();
String columnName="name";
rs=st.executeQuery("select "+ columnName+" from ad_org ");
public void MethodName(String strFieldName1, String strFieldName2, String strTableName)
{
//Code to connect with database
String strSQLQuery=String.format("select %s, %s from %s", strFieldName, strFieldName2, strTableName);
st=conn.createStatement();
rs=st.executeQuery(strSQLQuery);
//rest code
}
Below is the solution in java.
String strSelectString = String.format("select %s, %s from %s", strFieldName, strFieldName2, strTableName);