I have a mostly desktop programming background. In my spare time I dabble in web development, page faulting my way from problem to solution with some success. I have reached the point were I need to allow site logins and collect some data from a community of users (that is the plan anyway).
So, I realize there is a whole world of nefarious users out there who are waiting eagerly for an unsecured site to decorate, vandalize and compromise. If I am really lucky, a couple of those users might make their way to my site. I would like to be reasonably prepared for them.
I have a UI to collect information from a logged in user and some of that information is rendered into HTML pages. My site is implemented with PHP/MySQL on the back end and some javascript stuff on the front. I am interested in any suggestions/advice on how I should tackle any of the following issues:
Cross Site Scripting : I am hoping this will be reasonably simple for me since I am not supporting marked down input, just plain text. Should I be just scanning for [A-Za-z ]* and throwing everything else out? I am pretty ignorant about the types of attacks that can be used here, so I would love to hear your advice.
SQL injection : I am using parametized queries (mysqli) here , so I am hoping I am OK in this department. Is there any extra validation I should be doing on the user entered data to protect myself?
Trollish behaviour : I am supporting polylines drawn by the user on a Google Map, so (again if I am lucky enough to get some traffic) I expect to see a few hand drawn phallices scrawled across western Europe. I am planning to implement some user driven moderation (flag inaproriate SO style), but I would be interested in any other suggestions for discouraging this kind of behavior.
Logins : My current login system is a pretty simple web form, MySQL query in PHP, mp5 encoded password validation, and a stored session cookie. I hope the system is simple enough to be secure, but I wonder if their are vulnerabilies here I am not aware of?
I hope I haven't been too verbose here and look forward to hearing your comments.
Your first problem is that you are concerned with your UI. A simple rule to follow is that you should never assume the submitted data is coming from a UI that you created. Don't trust the data coming in, and sanitize the data going out. Use PHP's strip_tags and/or htmlentities.
Certain characters (<,>,",') can screw up your HTML and permit injection, but should be allowed. Especially in passwords. Use htmlentities to permit the use of these characters. Just think about what would happen if certain characters were output without being "escaped".
Javascript based checks and validation should only be used to improve the user experience (i.e. prevent a page reload). Do not use eval except as an absolute last resort.
Cross Site Scripting can be easily taken care of with htmlentities, there is also a function called strip tags which removes the tags from the post and you'll note that this allows you to whitelist certain tags. If you do decide to allow specific tags through in the future keep in mind that the attributes on these tags are not cleaned in any way, this can be used to insert javascript in the page (onClick etc.) and is not really recommended. If you want to have formatting in the future I'd recommend implementing a formatting language (like [b] for bold or something similar) to stop your users from just entering straight html into the page.
SQL Injection is also easily taken care of as you can prepare statements and then pass through the user data as arguments to the prepared statement. This will stop any user input from modifying the sql statement.
CSRF (Cross-Site Request Forgery) is an often overlooked vulnerability that allows an attacker to submit data from a victims account using the form. This is usually done either by specifying your form get string for an img src (the image loads for the victim, the get loads and the form is processed, but the user is unaware ). Additionally if you use post the attacker can use javascript to auto-submit a hidden form to do the same thing as above. To solve this one you need to generate a key for each form, keep one in the session and one on the form itself (as a hidden input). When the form is submitted you compare the key from the input with the key in the session and only continue if they match.
Some security companies also recommend that you use the attribute 'autocomplete="off"' on login forms so the password isn't saved.
Against XSS htmlspecialchars is pretty enough, use it to clear the output.
SQL injection: if mysql parses your query before adds the parameters, afaik its not possible to inject anything malicious.
I would look into something else besides only allowing [A-Za-z]* into your page. Just because you have no intention of allowing any formatting markup now doesn't mean you won't have a need for it down the line. Personally I hate rewriting things that I didn't design to adapt to future needs.
You might want to put together a whitelist of accepted tags, and add/remove from that as necessary, or look into encoding any markup submitted into plain text.
Related
I want to display the user's name on each page after they log in. Once I've retrieved their name from the database, what's the best way of storing that name in terms of speed and complexity of code? I've looked at sessions and cookies as options but wondered which is better or if some other way (like persisting a base ViewModel) is recommended.
I just don't want to have to go back to the database each page just to display some simple text.
In the end I went with putting all the pretty into cookies and reading them in the _Layout page.
Write once, read many and as the values are stored on the end-user's computer so the browser can pick them up locally, rather than from the server in any fashion and if someone hacks the values, it doesn't matter as they're just used for prettification.
What is the best way of prevention from stored XSS ?
should every text field (even plain text) be sanitized server-side to prevent from XSS HTML using something like OWASP Java HTML Sanitizer Project?
or should the client protect itself from XSS bugs by applying XSS prevention rules?
The problem with the first solution is that data may be modified (character encoding, partial or total deletion...). Which can alter the behavior of the application, especially for display concerns.
You apply sanitisation if and only if your data needs to conform to a specific format/standard and you are sure you can safely discard data; e.g. you strip all non-numeric characters from a telephone or credit card number. You always apply escaping for the appropriate context, e.g. HTML-encode user-supplied data when putting it into HTML.
Most of the time you don't want to sanitise, because you want to explicitly allow freeform data input and disallowing certain characters simply makes little sense. One of the few exceptions I see here would be if you're accepting HTML input from your users, you will want to sanitise that HTML to filter out unwanted tags and attributes and ensure the syntax is valid; however, you'd probably want to store the raw, unsanitised version in the database and apply this sanitisation only on output.
The gold standard in security is: Validate your inputs, and encode, not sanitize, your outputs.
First, validate the input server side. A good example of this would be a phone number field on a user profile. Phone numbers should only consist of digits, dashes, and perhaps a +. So why allow users to submit letters, special characters, etc? It only increases attack surface. So validate that field as strictly as you can, and reject bad inputs.
Second, encode the output according to its output context. I'd recommend doing this step server side as well, but it's relatively safe to do client side as long as you are using a good, well tested front-end framework. The main problem with sanitization is that different contexts have different requirements for safety. To prevent XSS when you are injecting user data into an HTML attribute, directly into the page, or into a script tag, you need to do different things. So, you create specific output encoders based on the output context. Entity encode for the HTML context, JSON.stringify for the script context, etc.
The client has to defend against this. For two reasons:
Because this is where the vulnerability happens. You might be calling a 3rd party API and they haven't escaped / encoded everything. It is better not trust anything.
Second, the API could be written for HTML page and for Android App. So why should the server html encode what some may consider html tags in a request when on the way back out it may be going to android app?
I am trying to understand the below injection and what it is trying to do. What is it trying to get? The only portion I understand is the union and select part, but the full injection I am unsure of and need help understanding.
action=&aid=1&_FILES%5Btype%5D%5Btmp_name%5D=%5C%27%20or%20mid=#%60%5C%27%60%20/!50000union//!50000select/1,2,3,(select%20CONCAT(0x7c,userid,0x7c,pwd)+from+%60%23#__admin%60%20limit+0,1),5,6,7,8,9%23#%60%5C%27%60+&_FILES%5Btype%5D%5Bname%5D=1.jpg&_FILES%5Btype%5D%5Btype%5D=application/octet-stream&_FILES%5Btype%5D%5Bsize%5D=4294
Well, first we can url decode the string:
action=
&aid=1
&_FILES[type][tmp_name]=\' or mid=#`\'`/!50000union//!50000select/1,2,3,(select CONCAT(0x7c,userid,0x7c,pwd) from `##__admin` limit 0,1),5,6,7,8,9##`\'`
&_FILES[type][name]=1.jpg
&_FILES[type][type]=application/octet-stream
&_FILES[type][size]=4294
One of these parameters sticks out as pretty suspicious.
[tmp_name]=\' OR mid=#`\'`
/!50000union/
/!50000select/1,2,3,
(select CONCAT(0x7c,userid,0x7c,pwd)
from `##__admin`
limit 0,1)
,5,6,7,8,9##`\'`
In plain english, it's injecting a select query to get usernames and passwords in a format like 0x7c<user>0x7c<password> from the ##__admin table (which, according to #DCoder is likely a placeholder for the actual table where these values would be kept) and appending it to your original select.
The !50000 stuff is for bypassing your web application firewall (if you have one). If you don't, then it may just be a bot or automated attempt. Or someone following a script to see what works. The numbers aren't really useful - it may be for evading a firewall or just for debugging purposes for the attacker to see how the output looks. It's hard to tell without being able to run it.
Here's what the SQL the attacker is trying to run would look like in 'plain SQL':
select
userid,
pwd
from
`##__admin`
Do you have a table like this? When you go to this url for your site, does it dump the user table? If not, then you may not even have a problem and it is just an automated scan. You may still have issues with SQL injection, even if it doesn't work, but having this in your logs is not evidence of a breach... it's definitely a red flag though.
It's adding extra columns to the result recordset, with user/pwd information. So in essence, the user wants to collect user accounts he or she wants to abuse.
It have to be noted that SQL injection (if any) is made possible by another vulnerability.
It is clear that this application is depending (or at least it is believed by the malicious user) on the some sort of homebrewed implementation of register_globals. A worst implementation ever.
To make this code work, the application have to take GET variables, and blindly convert them in global variables, making $_FILE array to appear not from internal process but from mere GET request.
This is my first question on stack overflow and I have taken a lot of time to search for the similar question but surprisingly could not find one.
So I read that no data should be trusted, whether from a client or that which is coming out of a database. Now while there are lots of examples that show how to sanitize data from a user ($_POST or $_GET), I could not find one that shows how the data from a database should be sanitized.
Now maybe it's the same as the data coming from a user / client (that's what I think it should be) but I found no example of it. So I am asking it just to make sure.
So for example if the result of a query yields as follows:-
$row=mysqli_fetch_assoc($result);
$pw = $row['Password'];
$id = $row['ID'];
$user = $row['Username'];
then do the variables $pw, $id and $user have to be sanitized before they should be used in the program? If so, then how ?
Thanks to all.
Your thinking is back to front here. By the time you are able to sanitise inputs using php, it's probably too late. The data is already in php. You don't sanitise inputs. You:
validate input & sanitise output
Normally a database is wrapped by the application tier. So the only data in there should have been filtered and escaped by your code. You should be able to trust it. But even then, in a relational database the data is fairly strongly typed. Hence there is little scope for attacking php from the data tier.
But you should be sanitising (escaping or encoding) any output. How you do that depends on where and how you are sending the data, hence it should be done at the point where it leaves php, not the point where it enters php. And the method you use (mysqli_escape, HTMLentities, base64, urlencode.....) Should be appropriate to where the data is going. Indeed it is better practice to change the representation of a copy of the data (and discard it after use) rather than the original.
It depends... How are you accessing this database? Who works on / maintains it? Going in is definitely a far bigger concern. However, if you wanted to sanitize it coming out of a database you need to know what you are sanitizing for. If you want to sanitize web traffic against XSS you'd probably want to remove all url's not on a whitelist, perhaps script tags and a few other things as well. Are you sanitizing data going into a C/C++ program? Then you probably want to make sure you're protecting yourself against buffer overflow issues as this is a legitimate avenue of attack.
I'm drawing some assumptions about your design here but I'm going to assume you're just working on the model aspect of an MVC application using PHP. PHP, in this case, has been most vulnerable to SQL Injection attacks on the backend, and XSS (cross site scripting) attacks on the front end. (NOTE: This isn't a PHP problem exclusively, this is a problem in all programming and different languages provide different solutions to different problems. Remember - you need to know what you're sanitizing for what reason. There is no one size fits all.
So really, unless you are sanitizing against something universal in all the code this model will sanitize for, you probably don't want to sanitize here. XSS would be a bigger concern to you now than sql injection... the way out is too late to stop an injection attack.
To take some liberty just to get the juices flowing - From a security standpoint, given your code seems to revolve around authentication, I would be much more immediately concerned around how you are storing and processing your credentialing data. A few things should definitely be doing:
Running the password through a secure, 1-way hash BEFORE storage (such as BCrypt).
Salting these hashes (with a different salt for EACH user) before storing them in the database to protect your user's data from things such as rainbow table attacks.
Using TLS for all communications.
Establishing and maintaining a secure session (track user-login without exposing password data with every single request sent, amongst other things).
I submitted data up to a controller in Grails and did a javascript injection which worked. I was surprised as I figured the default would be to encode parameters as they came into the controllers. Can I set this easily so that all parameters are encoded when they hit the controller? Also, am I safe to do a GORM create with the text as it came up, or is this vulnerable to SQL injection? I see in the guide how to prevent SQL Injection for a find query, but what about object creation?
I also saw that there is an encodeAsHTML method that I can call to encode on the way back down to the client. Wouldn't I want to do this before it went into the database so that I only have to encode once? Thanks!
User Input
The idea of "sanitizing your inputs" (or pre-encoding or pre-escaping) your content is a terrible one. It does not actually protect you when you really need it, and leads to all sorts of design headaches. Even PHP finally dumped the technique.
It's always better to handle the data via proper APIs correctly, which eliminates the risk. For example, SQL injections is absolutely eliminated using prepared statements or statements with placeholders for the content. This technique has been around for a very long time (as long as I've using Java & SQL).
Grails (GORM) automatically handles encoding any content that is saved via the objects, including setting a single property, creating a new object and saving it, or setting properties via obj.properties = params or something similar.
As long as you are using GORM, there is no risk of SQL injection.
Content Storage
Also, it's generally considered incorrect to store the already-encoded information in the database, as that encoding would only be correct for a given display type (such as HTML). If you instead wanted to render it using JSON, the HTML encoding is incorrect. XML is also slightly different, and there are times when you might prefer plain text, too.
Instead, you generally should store the raw (UTF8 or similar) data in the database, and convert it to the correct display type when it is being rendered for display. Note that it's converted when it's being rendered — this doesn't necessarily mean every time you send it to the client. You can use a variety of caching techniques to make sure this doesn't happen too often — including the new cache plugin added to Grails 2.1.
Preventing XSS Attacks
One highly recommended technique, however, is to set the default view codec to HTML, using the grails.views.default.codec option, like this:
grails.views.default.codec = 'html'
This will only affect GSPs, and only content echoed using dollar-sign syntax (${foo}). This gives you the flexibility of overriding this behavior using tags (the recommended way) or the <%= %> syntax for one-off situations. It should, however, provide a decent catch to prevent XSS attacks in general.
Performance Considerations
One final note: the concern about encoding the content as HTML being a performance issue would be considered premature optimization. Chances are extremely high that any performance bottlenecks would be somewhere else, and not in the encoding of the content. Build your application first — using a good design — and optimize later after you can benchmark and analyze the running application.