When using SQL in conjunction with another language what data must be escaped? I was just reading the question here and it was my understanding that only data from the user must be escaped.
Also must all SQL statements be escaped? e.g. INSERT, UPDATE and SELECT
EVERY type of query in SQL must be properly escaped. And not only "user" data. It's entirely possible to inject YOURSELF if you're not careful.
e.g. in pseudo-code:
$name = sql_get_query("SELECT lastname FROM sometable");
sql_query("INSERT INTO othertable (badguy) VALUES ('$name')");
That data never touched the 'user', it was never submitted by the user, but it's still a vulnerability - consider what happens if the user's last name is O'Brien.
Most programming languages provide code for connecting to databases in a uniform way (for example JDBC in Java and DBI in Perl). These provide automatic techniques for doing any necessary escaping using Prepared Statements.
All SQL queries should be properly sanitized and there are various ways of doing it.
You need to prevent the user from trying to exploit your code using SQL Injection.
Injections can be made in various ways, for example through user input, server variables and cookie modifications.
Given a query like:
"SELECT * FROM tablename WHERE username= <user input> "
If the user input is not escaped, the user could do something like
' or '1'='1
Executing the query with this input will actually make it always true, possibly exposing sensitive data to the attacker. But there are many other, much worse scenarios injection can be used for.
You should take a look at the OWASP SQL Injection Guide. They have a nice overview of how to prevent those situations and various ways of dealing with it.
I also think it largely depends on what you consider 'user data' to be or indeed orignate from. I personally consider user data as data available (even if this is only through exploitations) in the public domain, i.e. can be changed by 'a' user even if it's not 'the' user.
Marc B makes a good point however that in certain circumstances you may dirty your own data, so I guess it's always better to be safer than sorry in regards to sql data.
I would note that in regards to direct user input (i.e. from web forms, etc) you should always have an additional layer server side validation before the data even gets near a sql query.
Related
My client is making database searches using a django webapp that I've written. The query sends a regex search to the database and outputs the results.
Because the regex searches can be pretty long and unintuitive, the client has asked for certain custom "wildcards" to be created for the regex searches. For example.
Ω := [^aeiou] (all non-vowels)
etc.
This could be achieved with a simple permanent string substitution in the query, something like
query = query.replace("Ω", "[^aeiou]")
for all the elements in the substitution list. This seems like it should be safe, but I'm not really sure.
He has also asked that it be possible for the user to define custom wildcards for their searches on the fly. So that there would be some other input box where a user could define
∫ := some other regex
And to store them you might create a model
class RegexWildcard(models.Model):
symbol = ...
replacement = ...
I'm personally a bit wary of this, because it does not seem to add a whole lot of functionality, but does seem to add a lot of complexity and potential problems to the code. Clients can now write their queries to a db. Can they overwrite each other's symbols?
That I haven't seen this done anywhere before also makes me kind of wary of the idea.
Is this possible? Desirable? A great idea? A terrible idea? Resources and any guidance appreciated.
Well, you're getting paid by the hour....
I don't see how involving the Greek alphabet is to anyone's advantage. If the queries are stored anywhere, everyone approaching the system would have to learn the new syntax to understand them. Plus, there's the problem of how to type the special symbols.
If the client creates complex regular expressions they'd like to be able to reuse, that's understandable. Your application could maintain a list of such expressions that the user could add to and choose from. Notionally, the user would "click on" an expression, and it would be inserted into the query.
The saved expressions could have user-defined names, to make them easier to remember and refer to. And you could define a syntax that referenced them, something otherwise invalid in SQL, such as ::name. Before submitting the query to the DBMS, you substitute the regex for the name.
You still have the problem of choosing good names, and training.
To prevent malformed SQL, I imagine you'll want to ensure the regex is valid. You wouldn't want your system to store a ; drop table CUSTOMERS; as a "regular expression"! You'll either have to validate the expression or, if you can, treat the regex as data in a parameterized query.
The real question to me, though, is why you're in the vicinity of standardized regex queries. That need suggests a database design issue: it suggests the column being queried is composed of composite data, and should be represented as multiple columns that can be queried directly, without using regular expressions.
I ask this question with a bit of sheepishness because I should know the answer. Could someone be kind and explain if and how injection could occur in the following code?
<cfquery>
select * from tableName
where fieldName = '#value#'
</cfquery>
I'm specifically curious about injection attempts and other malicious input, not about best practices or input validation for handling "normal" user input. I see folks strongly advocating use of CFQueryParam, but don't think I see the point. If user input has been validated for consistency to the database schema (e.g. so that input must be numeric for numerical database fields), is there anything else gained by using CFQueryParam? What does <cfqueryparam CFSQLType = "CF_SQL_VARCHAR"> do that '#value#' doesn't do?
Update:
While this answers part of your question, Peter's response is better, in that it directly addresses your question of "Why use cfqueryparam, when CF automatically adds protection by escaping single quotes?". Answer: In short, because the latter does not always work. Bind variables do.
It says in the docs "escapes string variables in single-quotation
marks" but doesn't CF already "magically" do this in CF query tag when
you wrap evaluated variables in single quotes?
Yes, most versions automatically escape single quotes as a protection measure for those not using cfqueryparam. However, as Scott noted above, it is better to use cfqueryparam (ie bind variables) because they ensure parameters are not executed as sql commands. Bind variables work, even in cases where the automatic escaping does not, as Peter's answer demonstrates.
That said, sql injection protection is really just a side effect of using bind variables. The primary reason to use bind variables is performance. Bind variables encourage databases to re-use query plans, instead of creating a new plan every time your #parameters# change. That cuts down on compilation time, improving performance.
Cfqueryparam also has a number of other benefits:
Provides data type checking (length, value, type, ...)
Provides attributes that simplify handling of "lists" and null values
Performs data type checking before any sql is sent to the database, preventing wasted database calls
While it does not really apply to string columns, IMO another big reason to use it is accuracy. When you pass a quoted string to the database, you are relying on implicit conversion. Essentially you are leaving it up to the database to figure out how to best perform the comparison, and the results are not always what you were expecting. (Date strings are a prime example). You may end with inaccurate results, or sometimes slower queries, depending on how the database decides to execute the sql. Using cfqueryparam avoids those issues by eliminating the ambiguity.
doesn't CF already "magically" do this in CF query tag when you wrap evaluated variables in single quotes?
Yep, it'll convert ' to '' for you.
Now guess what SQL you get from this code:
<cfset value = "\'; DROP TABLE tableName -- " />
<cfquery>
select * from tableName
where fieldName = '#value#'
</cfquery>
The cfqueryparam tag works; using query params solves SQL injection.
Any custom written attempts at validating, sanitizing, or escaping (all separate things, btw) are, at best, only as good as the developer's knowledge of the database system the code is running against.
If the developer is unaware of other escape methods, or if the values are modified between validation/escaping and them being rendered into SQL, or even if the codebase is ported to another database system and seems to be fine, there's a chance of custom code breaking down.
When it comes to security, you don't want chances like that. So use cfqueryparam.
To answer the first part of your question, setting your #value# variable to the following:
someValue'; DELETE FROM tableName WHERE '1' = '1
would result in this query being executed:
<cfquery>
select * from tableName
where fieldName = 'someValue'; DELETE FROM tableName WHERE '1' = '1'
</cfquery>
I would like to build a safe dynamic select statement that can handle multiple WHERE clauses.
For example the base SQL would look like:
SELECT * FROM Books Where Type='Novel'
I would pass the function something like:
SafeDynamicSQL("author,=,Herman Melville","pages,>,1000");
Which would sanitize inputs and concatenate like:
SELECT * FROM Books Where Type='Novel' AND author=#author AND pages>#pages
The function would sanitize the column name by checking against an array of predefined column names. The operator would only be allowed to be >,<,=. The value would be added as a normal paramater.
Would this still be vulnerable to SQL injection?
There will be some string manipulation and small loops which will affect performance but my thoughts are that this will only take a few milliseconds compared to the request which on average take 200ms. Would this tax the server more than I am thinking if these requests are made about once a second?
I know this isn't best practice by any means, but it will greatly speed up development. Please give me any other reasons why this could be a bad idea.
It looks like you're reinventing any number of existing ORM solutions which offer a similar API for creating WHERE clauses.
The answer to your question hinges on what you mean by "The value would be added as a normal paramater." If by that you mean performing string concatenation to produce the string you showed then yes, that would still be subject to SQL injection attack. If you mean using an actual parameterized query then you would be safe. In the later case, you would produce something like
SELECT * FROM Books Where Type='Novel' AND author=? AND pages > ?
and then bind that to a list of values like ['Herman Melville', 1000]. Exactly what it would look like depends on what programming language you're using.
Finally, if you pursue this path I would strongly recommend changing from comma-delimited arguments to three separate arguments, you'd save yourself a lot of programming time.
Pretty much any code that appends together (or interpolates) strings to create SQL is bad form from a security point of view, and is probably subject to some SQLi attack vector. Just use bound parameters and avoid the entire problem; avoiding SQL injection is super-easy.
I know it's a simple question, but in everything I've read, I've never seen this spelled out specifically.
If you do a query on a page, do you need to worry about SQL injection attacks? Or is it only a problem when you ask the user for input?
Thanks!
You don't have to have user input to suffer a SQL injection attack.
Let's say you have a product page that is called using a URL such as this:
product.aspx?ID=123
And in your code you have a query constructed such as this:
string sql = "SELECT * FROM Products WHERE ID = " + Request.Querystring["ID"];
Someone could call your page with this url:
product.aspx?ID=123;DROP Table Students;
And bam, you've just been had.
In addition to ANYTHING that can be passed in via a user, querystring, post, cookie, browser variable, etc. I think it is just good practice to always use parameters, even if you have the literals in your code. For example:
if(SomeCondition)
{
sql = "Select * from myTable where someCol = 'foo'";
}
else
{
sql = "Select * from myTable where someCol = 'bar'";
}
this may be injection safe, but your RDBMS will cache them as two different queries.
if you modiy it to this:
sql = "Select * from myTable where someCol = #myParam";
if(SomeCondition)
{
myCommand.Parameters.Add("#myParam").value = "foo";
}
else
{
myCommand.Parameters.Add("#myParam").value = "bar";
}
You achieve the same result but the RDBMS will only cache it as one query, substituting the parameter at runtime. I use it as a rule of thumb to ALWAYS use parameterized queries, just to keep things consistent, not to mention a slight cache improvement.
SQL injection is caused by unsanitized data. You should always always always sanitize data going into a database. Not just for SQL injection, but also for making your app just work.
For example, some systems won't use my name because it has a ' character in it, and their database is not sanitized. I did not enter my name, my name was taken from another database. Doesn't matter -- the data should be sanitized.
SQL Injection snippets can also come in from the QueryString (aka "URL arguments") passed in with the GET method instead.
As hinted by Billy O'Neal [single quote intended ;-) ], any piece of data that is not intrinsic to the program (or to its very trusted back-end), should be "sanitized". The Sanitizing term seems to imply to be a sophisticated process, but in effect it typically means little more than:
[may vary with your specific SQL server make]
remove (or escape) single quotes characters embedded within a string
watch from strings exceeded the length of the underlying SQL column (in particular if such length is readily long)
A possible reason for the idea that HTTP Forms would be the only source of SQL injection snippets is that a -valid- recommendation is to ensure that one gets the user-supplied submitted text from the Request's form exclusively. Several Web Application frameworks expose the HTTP request as an object which exposes, by default, all key-values pairs from either the QueryString, from a Form, or even from cookies, accessible as from a single hash. While this can be practical for applications that sometimes get the info from a form an sometimes from the querystring, this can facilitate the work of would-be-injectors, because it is easier to craft a URL than a Form. (But with the proper tool, one can also fake a POST request as well...)
No, there are several other cases. For example, you may have some of the variables as a querystring passed into a php page. The 'user' could modify that string to include some dodgy scripting.
http://en.wikipedia.org/wiki/SQL_injection includes a large section on the types of vulnerabilities and how to combat them effectively.
To summarize - any type of input from the user that is used in SQL queries is a potential target of sql injection
Also consider preventing against cross-site-scripting ("XSS").
SQL Injections is possible if you use any kind of data that comes from the browser. It could be form data, querystring data, cookie values, or even data from the request header.
The obvious and easy ways in is the form data and querystring data, but anything that comes from the browser could be spoofed.
Anything that the code takes as input from the HTTP request can be a SQL injection vector:
POST/PUT content
GET URL parameters
Cookies
At a higher level these show up as $_REQUEST or Page.Request values, session variable, it all depends on a miriad of factors. but ultimately, is not just POST forms. Although probably the most prvalent vector is form POST content and GET URL variables.
When the user can modify the values of the parameters of a query, then it can become a threat.
You need to worry about cross site scripting (XSS) attacks in this case if the data you are displaying on the page came from user submitted data.
ESCAPE INPUT, FILTER OUTPUT
As I concern you should never trust this variables: $_POST, $_GET, $_REQUEST, $_COOKIE even $_SERVER can contain malicious code. So ALWAYS make sure that inserted data match your expectation.
For example as an extra paranoid measure on validation email address you can encrypt email address with md5 like this:
"SELECT username FROM users WHERE MD5(email)='" . md5($_POST['email']) . "' AND active=1"
As a general rule parameterized queries should always be used.
It prevents malicious user input from being executed against your database (SQL injection attacks). [You should do user input validation as well to ensure that malicious code isn't rendered on the page and that JavaScript can be run against your server.]
It enables you to re-use your queries.
You can precompile your queries.
It organizes your input and makes it more readable. You might want to use the same parameter in more than one location.
It has better support for different data type such as dates, strings and the like. You won't run into problems with weird characters when you use parameterized queries.
In my use case I always generate parameter based queries. I have a wrapper that will always compile them so that if a second query gets executed in the same request path, it will run that much faster on the same connection. This takes a fair bit of work to setup, but is worth the performance gain in any medium to enterprise level system.
I agree that parameterisation is the best approach.
As an alternative (which might be easier to retro fit into your code, at least initially) doubling the single quotes in a string will prevent SQL Injection.
To take Neil N's example:
sql = "Select * From Products Where ID = " + Request.Querystring["ID"];
wrap the variable in a function that doubles the quotes, and wrap the varible with single quotes too.
sql = "Select * From Products Where ID = "
+ fnSQLSafeParam(Request.Querystring["ID"]);
The function would be something like (VBscript example):
Function fnSQLSafeParam(ByVal strStr)
If IsNull(strStr) or IsEmpty(strStr) then strStr = ""
fnSQLSafeParam = "'" & replace(Trim(CStr(strStr)), "'", "''") & "'"
End Function
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.