I am querying some data from the database and inserting data. Whenever the user inserts with ' I have a problem that the query does not regconize.
How can I get rid of that? should I use: string.replace(''', '"') ? or any other trick?
Thanks in advance.
You should be using parameterized queries. It's dangerous to insert unprocessed user input on a query, it's an open door to SQL-Injection attacks.
Those are queries in the form
SELECT * FROM USERS where USER_ID = ?
The value of ? is set programmatically with a query.setString(1, userId) call, and the driver takes care of escaping everything correctly. It's not a burden you want to have on your shoulders.
Besides to what Xavi López has posted (and you really should keep that in mind), to have a single quote in a string you need to write two single quotes, e.g.:
myString := 'I''m writing an answer';
This represents the string I'm writing an answer.
Related
We have a database where our customer has typed "Bob's" one time and "Bob’s" another time. (Note the slight difference between the single-quote and apostrophe.)
When someone searches for "Bob's" or "Bob’s", I want to find all cases regardless of what they used for the apostrophe.
The only thing I can come up with is looking at people's queries and replacing every occurrence of one or the other with (’|'') (Note the escaped single quote) and using SIMILAR TO.
SELECT * from users WHERE last_name SIMILAR TO 'O(’|'')Dell'
Is there a better way, ideally some kind of setting that allows these to be interchangeable?
You can use regexp matching
with a_table(str) as (
values
('Bob''s'),
('Bob’s'),
('Bobs')
)
select *
from a_table
where str ~ 'Bob[''’]s';
str
-------
Bob's
Bob’s
(2 rows)
Personally I would replace all apostrophes in a table with one query (I had the same problem in one of my projects).
If you find that both of the cases above are valid and present the same information then you might actually consider taking care of your data before it arrives into the database for later retrieval. That means you could effectively replace one sign into another within your application code or before insert trigger.
If you have more cases like the one you've mentioned then specifying just LIKE queries would be a way to go, unfortunately.
You could also consider hints for your customer while creating another user that would fetch up records from database and return closest matches if there are any to avoid such problems.
I'm afraid there is no setting that makes two of these symbols the same in DQL of Postgres. At least I'm not familiar with one.
I inherited a database where user input fields are stored as a comma delimited string. I know. Lame. I want a way to parse these fields in a SELECT query where there are three segments of varying number of characters. Counter to all the recommendations that I insert fields into a new table or create a stored procedure to do this, this is what I came up with. I'm wondering if anyone sees any flaw in doing this as a select query (where I can easily convert from string to parsed and back again as need be).
Field_A
5,25,89
So to get the left segment, which is the most straightforward:
Field_1: Left$([Field_A],InStr([Field_A],",")-1)
To get the right-most segment:
Field_3: Right$([Field_A],Len([Field_A])-InStrRev([Field_A],","))
Middle segment was the trickiest:
Field_2: Mid([Field_A],InStr([Field_A],",")+1,InStrRev([Field_A],",")-InStr([Field_A],",")-1)
So the result is:
Field_1 Field_2 Field_3
5 25 89
Any consenting opinions?
Well, if you insist on going down this road......
This might be easier and more adaptable. Create a function in a module:
Public Function GetValueFromDelimString(sPackedValue As String, nPos As Long,
Optional sDelim As String = ",")
Dim sElements() As String
sElements() = Split(sPackedValue, sDelim)
If UBound(sElements) < nPos Then
GetValueFromDelimString = ""
Else
GetValueFromDelimString = sElements(nPos)
End If
End Function
Now in your query you can get any field in the string like this:
GetValueFromDelimString([MultiValueField],0) AS FirstElement, GetValueFromDelimString([MultiValueField],1) AS SecondElement, etc.
I feel like I am buying beer for a minor, encouraging this type of behavior :)
It sounds like you're not asking for information on how to parse a comma-delimited field into different fields, but rather looking for people to support you in your decision to do so, yes?
The fact, as you've already discovered, is that you can indeed do this with skillful application of functions in your SQL field definitions. But that doesn't mean that you should.
In the short run, it's an easy way to achieve your goals as data manager, I'll grant you that. But as a long-term solution it's just adding another layer of complexity to what seems like a poorly-designed database (I know that the latter is not your fault -- I too have inherited my share of "lame" databases).
So I applaud you on "getting the job done" for now, but would advise you to listen to "all the recommendations that you insert fields into a new table" -- they're good recommendations. It'll take more planning and effort, but in the long run you'll have a better database. And that will make everything you do with it easier, faster, and more reliable.
This is an old thread, but someone might search it. You can also do the same strategy as an update query. That way you can keep the original CSV and have 3 new destination fields that can be calculate and recalculated depending on your application purposes.
Simple, a SQL injection attack in as few characters as possible. Note, I'm not trying to prevent SQL injection attacks by limiting inputs to a certain size, but rather am genuinely curious how many characters is needed to execute even the simplest attack.
For posterity sake, let's say the smallest table name is 4 characters, e.g., "user". Please factor that in.
1 Character is the smallest unit that you have control over. The question depends heavily on what you're doing. For instance, if you're dealing with an interface to delete your profile from a site, and you send '%' instead of your name:
"Delete from Users where name like '"+username+"'"
then setting your username to % will delete all the users.
When injecting into a string literal:
';drop database;--
Suppose the query was generated like this
"Select * from user where userid = " + myVar
1; delete from user;
how about this one:
' OR 1=1 --
When I started to write the first SQL-Statements in my programs I felt quite comfortable with protecting myself against SQL-Injection with a very simple method that a colleague showed me. It replaced all single quotes with two single quotes.
So for example there is a searchfield in which you can enter a customername to search in the customertable. If you would enter
Peter's Barbershop
The SELECT Statement would look like
SELECT *
FROM Customers
WHERE Customername = 'Peter''s Barbershop'
If now an attacker would insert this:
';DROP TABLE FOO; --
The statement would look like:
SELECT *
FROM Customers
WHERE Customername = ''';DROP TABLE FOO;--'
It would not drop any table, but search the customertable for the customername ';DROP TABLE FOO;-- which, I suppose, won't be found ;-)
Now after a while of writing statements and protecting myself against SQL-Injection with this method, I read that many developers use parameterized statements, but I never read an article where "our" method was used. So definitely there is a good reason for it.
What scenarios would parameterized statements cover but our method doesn't? What are the advantages of parameterized statements compared to our method?
Thanks
Philipp
The parametrized queries has more proc than the defence to sql-injection.
It solves problem with date & time formating & parsing.
You can prepare execution plan for parametrized query.
The sql-injection protection.
I can't remember now for another pros :).
However the way "double every quotes" has problem with fields with limited character length.
For example:
The page has box for "nickname" which can be 10 character long.
The user insert "Don't care" - the exact 10 characters.
Now if you double the quotes, the value has 11 characters and the database will "cut" it, and you got another value in db than user typed.
So I recommend the parameters.
One big dis-advantage is that your solution relies on a developer remembering to add the character, obviously the compiler won't complain. That is dangerous.
Secondly, performance should be enhanced with parameterized SQL statements, as Jeff points out here (in 2005!!!).
One advantage is that the driver itself will determine what he has to escape and what doesn't need to be escaped. Your method could be broken with an input like this:
\'; DROP TABLE foo;--
Which would result in
SELECT *
FROM Customers
WHERE Customername = '\'';DROP TABLE FOO;--'
The first quote gets escaped, the second doesn't and closes the string.
Short answer:
You should use parameterized queries simply because the database server knows better than you do which characters need to be escaped.
Long answer:
' is not necessarily the only special character that needs escaping. These special characters differ from DB server to DB server. MySQL, for example, uses \ as an escape character as well (unless sql_mode=NO_BACKSLASH_ESCAPES is set). Therefore, '' and \' mean the same thing.
This is not true of, say, Oracle.
What are the advantages of
parameterized statements compared to
our method?
The advantage is that it's harder to make a mistake; you can't do the parameterized method, and forget to replace the quotes. Also, replacing quotes is vulnerable if you do it twice.
The disadvantage of parameterized queries (and the reason I never use them) is complexity. You can write ten times as many ad-hoc queries before you get RSI.
If I remove all the ' characters from a SQL query, is there some other way to do a SQL injection attack on the database?
How can it be done? Can anyone give me examples?
Yes, there is. An excerpt from Wikipedia
"SELECT * FROM data WHERE id = " + a_variable + ";"
It is clear from this statement that the author intended a_variable to be a number correlating to the "id" field. However, if it is in fact a string then the end user may manipulate the statement as they choose, thereby bypassing the need for escape characters. For example, setting a_variable to
1;DROP TABLE users
will drop (delete) the "users" table from the database, since the SQL would be rendered as follows:
SELECT * FROM DATA WHERE id=1;DROP TABLE users;
SQL injection is not a simple attack to fight. I would do very careful research if I were you.
Yes, depending on the statement you are using. You are better off protecting yourself either by using Stored Procedures, or at least parameterised queries.
See Wikipedia for prevention samples.
I suggest you pass the variables as parameters, and not build your own SQL. Otherwise there will allways be a way to do a SQL injection, in manners that we currently are unaware off.
The code you create is then something like:
' Not Tested
var sql = "SELECT * FROM data WHERE id = #id";
var cmd = new SqlCommand(sql, myConnection);
cmd.Parameters.AddWithValue("#id", request.getParameter("id"));
If you have a name like mine with an ' in it. It is very annoying that all '-characters are removed or marked as invalid.
You also might want to look at this Stackoverflow question about SQL Injections.
Yes, it is definitely possible.
If you have a form where you expect an integer to make your next SELECT statement, then you can enter anything similar:
SELECT * FROM thingy WHERE attributeID=
5 (good answer, no problem)
5; DROP table users; (bad, bad, bad...)
The following website details further classical SQL injection technics: SQL Injection cheat sheet.
Using parametrized queries or stored procedures is not any better. These are just pre-made queries using the passed parameters, which can be source of injection just as well. It is also described on this page: Attacking Stored Procedures in SQL.
Now, if you supress the simple quote, you prevent only a given set of attack. But not all of them.
As always, do not trust data coming from the outside. Filter them at these 3 levels:
Interface level for obvious stuff (a drop down select list is better than a free text field)
Logical level for checks related to data nature (int, string, length), permissions (can this type of data be used by this user at this page)...
Database access level (escape simple quote...).
Have fun and don't forget to check Wikipedia for answers.
Parameterized inline SQL or parameterized stored procedures is the best way to protect yourself. As others have pointed out, simply stripping/escaping the single quote character is not enough.
You will notice that I specifically talk about "parameterized" stored procedures. Simply using a stored procedure is not enough either if you revert to concatenating the procedure's passed parameters together. In other words, wrapping the exact same vulnerable SQL statement in a stored procedure does not make it any safer. You need to use parameters in your stored procedure just like you would with inline SQL.
Also- even if you do just look for the apostrophe, you don't want to remove it. You want to escape it. You do that by replacing every apostrophe with two apostrophes.
But parameterized queries/stored procedures are so much better.
Since this a relatively older question, I wont bother writing up a complete and comprehensive answer, since most aspects of that answer have been mentioned here by one poster or another.
I do find it necessary, however, to bring up another issue that was not touched on by anyone here - SQL Smuggling. In certain situations, it is possible to "smuggle" the quote character ' into your query even if you tried to remove it. In fact, this may be possible even if you used proper commands, parameters, Stored Procedures, etc.
Check out the full research paper at http://www.comsecglobal.com/FrameWork/Upload/SQL_Smuggling.pdf (disclosure, I was the primary researcher on this) or just google "SQL Smuggling".
. . . uh about 50000000 other ways
maybe somthing like 5; drop table employees; --
resulting sql may be something like:
select * from somewhere where number = 5; drop table employees; -- and sadfsf
(-- starts a comment)
Yes, absolutely: depending on your SQL dialect and such, there are many ways to achieve injection that do not use the apostrophe.
The only reliable defense against SQL injection attacks is using the parameterized SQL statement support offered by your database interface.
Rather that trying to figure out which characters to filter out, I'd stick to parametrized queries instead, and remove the problem entirely.
It depends on how you put together the query, but in essence yes.
For example, in Java if you were to do this (deliberately egregious example):
String query = "SELECT name_ from Customer WHERE ID = " + request.getParameter("id");
then there's a good chance you are opening yourself up to an injection attack.
Java has some useful tools to protect against these, such as PreparedStatements (where you pass in a string like "SELECT name_ from Customer WHERE ID = ?" and the JDBC layer handles escapes while replacing the ? tokens for you), but some other languages are not so helpful for this.
Thing is apostrophe's maybe genuine input and you have to escape them by doubling them up when you are using inline SQL in your code. What you are looking for is a regex pattern like:
\;.*--\
A semi colon used to prematurely end the genuine statement, some injected SQL followed by a double hyphen to comment out the trailing SQL from the original genuine statement. The hyphens may be omitted in the attack.
Therefore the answer is: No, simply removing apostrophes does not gaurantee you safety from SQL Injection.
I can only repeat what others have said. Parametrized SQL is the way to go. Sure, it is a bit of a pain in the butt coding it - but once you have done it once, then it isn't difficult to cut and paste that code, and making the modifications you need. We have a lot of .Net applications that allow web site visitors specify a whole range of search criteria, and the code builds the SQL Select statement on the fly - but everything that could have been entered by a user goes into a parameter.
When you are expecting a numeric parameter, you should always be validating the input to make sure it's numeric. Beyond helping to protect against injection, the validation step will make the app more user friendly.
If you ever receive id = "hello" when you expected id = 1044, it's always better to return a useful error to the user instead of letting the database return an error.