I have a web application where user can upload and view files. The user has a link next to the file (s)he has uploaded. Clicking on the link will open the file in the browser (if possible) or show the download dialog (of the browser). Meaning that, if the user upload an html/pdf/txt file it will be rendered in the browser but if it is a word document, it will be downloaded.
It is identified that rendering the HTML file in the browser could be a vulnerability - Cross Site Scripting.
What is the right solution to this problem? The two options I am currently looking at are:
to put Content-Disposition header in the response to make HTML files downloaded instead viewed in the browser.
to find some html scrubbing/sanitizing library to remove any javascript from the file before I serve it.
Looking at the gmail, they do the second approach (of scrubbing) with having a separate domain for the file download - may be to minimize/distract the attack surface. However in this approach the receiver gets a different file than what was sent. Which is not 'right' in my opinion; may be I am biased. In my case, the first one is easy to fix. But I wonder if that is enough, or is there any thing that I overlook!
What are your thoughts on these approaches? Or do you have any other suggestions?
Based on your description, I can see 3 posible attack types (maybe there are more):
Client side code execution
As you said, your web server may serve a file as HTML and run javascript code on the client. This can be avoided with Content-Disposition but I would go with MIME types control through Content-Type. I would define my known type of files (e.g. pdf, jpeg etc.) and serve them with their respective MIME type (e.g. application/pdf, image/jpeg etc.). Anything else I would serve it as application/octet-stream.
Server side code execution
Althougth I see this as an out of topic attack (since it involves other parts of your application and your server) be sure to avoid executing files on the server (e.g. PHP code through LFI). Your webserver should not access directly the files (e.g. again PHP), better store them somethere not accesible through a URL and retrive them on request.
Think if here you are able to reject files (e.g. reject .exe uploads) and ask the user to zip them first.
Trust issues
Since the files are under the same domain, the files will be accesible from javascript (ajax or load as script) and other programs (or people) may trust your links. This is also related to the previous point, if you don't need unzipped exe files, don't allow them. Using an other domain may mitigate some trust problems.
Other ideas:
Zip all files uploaded
Scan each file with antivirus software
PS: For me sanitization would not work in your case. The risk of missing something is too high.
Related
To render on threejs, we need some images(jpg/png) and , jsons(uv data). All these files are stored in respective folders and the files visible for clients to look at.
I use django/python to start a local server, python code is compiled to .pyc & js code is obfuscated. But the folder structure is accessible for Casual Users. In threejs, we use tex_loader and json_loader functions to which the file paths are given as inputs. Was looking at ways of securing the behind the scenes work.
Happened to read about custom binary formats, but that felt like a lot of work.
or giving access to files only for certain process starting through django/web browser?
Are there any available easy to deploy solutions to protect our IP ?
An option would be to only serve the files to authenticated users. This could be achieved by having an endpoint on your backend like:
api/assets/data.json
and the controller in the backend would receive the file name(data.json), the code could check if the user requesting the endpoint is authenticated and if so read the file from the file system(my-private-folder/assets/data.json) and return it as file with correct mime-type to the browser.
Is anyone familiar with DNN 9 platform here? If so could someone direct me how to upload an svg file to the server. In older version of DNN(8,7 etc) there was a setting in the Host List settings where you could enable the file type, however in DNN these pages have been removed from the user interface.
The following command has been run in SSMS:
INSERT INTO Lists (ListName, Value, Text, DefinitionID, SystemList)
VALUES ('ImageTypes', 'svg', 'Scalable Vector Graphics', '-1', 'True');
This created a new line in the database, however when I try to upload a svg file it still show wrong format (The Allowed Filetypes are: "bmp,gif,jpeg,jpg,png").
Can someone direct me perhaps where can the svg file type be enabled?
Many thanks!
The option to add file types is still there. It has been moved and has a different name. Go to:
Settings > Security > More
There is a tab there called More Security settings. There you will find the Allowable File Extensions
Some DNN sites allow users to upload certain files to their sites. A malicious can upload an SVG file which can contain some malicious code to steal some users’ sensitive data (cookies, etc.)
I want to export a table to an Excel file. I need to export a report.
ORA_EXCEL.new_document;
ORA_EXCEL.add_sheet('Sheet name');
ORA_EXCEL.query_to_sheet('select * from mytable');
ORA_EXCEL.save_to_blob(myblob);
I saved my table to blob.
How do I export/respond to the user (client)?
I need something that is simple to allow a user to be able to download an Excel file to their own computer. I tried doing this procedure in an Oracle workflow:
ORA_EXCEL.save_to_file('EXPORT_DIR', 'example.xlsx');
But this did not help, because it is saves the file to a directory on the server and I need it in the real server.
The way I have handled similar issues in the past was to work with the systems people to mount a directory from either a web server or file server on the Database server.
Then create a directory object so that the procedure can save to a location that is accessible to the user.
If the files are not sensitive and there are a limited number of users then a file server makes sense as it is then just a matter of giving the user access to the file share.
If files are sensitive or this is a large number or unknown users we then used the Web server and sent a email with a link to the user enabling them to download their file. Naturally there needs to be security built into this to stop people being able to download other users files.
We didn't just email the files as an attachment because...
1) Emails with attachments tend to get blocked
2) We always advise not to open attachments on emails. (Yes I know we advise not to click on links as well but nothing is perfect)
Who or what is invoking the production of the document?
If it´s done by an application, which the user is working on, this application can fetch the BLOB, stores it at f.e. TEMP-Directory and calls
System.Diagnostics.Process.Start("..."); to open it with the associated application. (see Open file with associated application)
If it´s a website, this one could stream the blob back as Excel-Mimetype (see Setting mime type for excel document)
Also you could store in an Oracle-DIRECTORY, but this one has to be on the server and should be a netword-share to be accessible for clients (which is rarely accepted in a productive environment!)
If MAIL isn´t the solution, then maybe FTP can be a way to store files in a common share. See UTL_TCP - Package, with this a FTP-transfer can be achieved (a bit hard to code, but there are solutions to find in the web) and I guess, professional tools that generate Office-documents out of Oracle-DB and distribute them do it like this.
I have a web resource which returns json content with Content-Type:application/json. Usually the content is displayed in browser directly but sometimes it's not, instead, a download prompt shows.
I know there's a header Content-Disposition:inline/attachment which can explictly tell browser whether to download or show. But if I don't specify this header, how does browser decide? What's its strategy?
From Mozilla's File types and download actions (emphasis mine):
When you click a link to download a file, the MIME type determines what action is taken. If you see an "Opening " dialog asking if you want to save the file or open it with a specified application, that normally means that your Mozilla application cannot handle the MIME type internally, no plugin is installed and enabled that can handle it and you have not previously selected a download action or helper application to always use for that type of file.
The browser comes preconfigured to handle basic formats like images. Plugins (which may be bundled with the browser) add handling for various common file types like pdfs. There can also be "helper applications", which means the browser downloads and forwards the file automatically to the application (such as a torrent magnet link opening your torrent client)
Everything else, it will ask until a user binds a default action (if the Content-Type is application/octet-stream, you can't set a default action). The other browsers work the same.
What Content-Type is specified in the header? If the browser doesn't know what it is, it probably defaults to application/octet-stream and prompts for download.
Here's a brief blog about it.
I've built an online system that allows users to download PDF files using ColdFusion. Users have to log in before they can download the files (PDF & Microsoft Office documents). (This application is only for our company staff.)
However, only today I found out that anyone with internet access can view the files. With only certain keywords such as 'Medical Form myCompanyName' in a Google search, they can view the PDF files using the browser.
How can I prevent this?
UPDATE
this is what my problem is. i've created a folder for all of the PDFs file. each of the files is called using ID from database. if let's say a user wanted to view Medical Form, the link would be: http://myApplication.myCompanyName/forms.cfm?Department=Account&filesID=001.
if the user copy this url & log out from system, he/she will not be able to view this file.(login page will be displayed)
However, without the url, other internet users sstill can view the pdf files just by search it on the net, and the search engine will gives a link that direct it to the folder itself, without having to login.
Example:
Medical Form's pdf file is stored in a folder named Document. when an internet user search for Medical Form, the search engine will link it to: http://myApplication.myCompanyName/Document/Medical%20Form.pdf
we have lots of PDF files in this folder and most of it are confidential, and for internal view purpose only. in php, we can disable this by using .htaccess. i'd like to know if there's anything like this for coldfusion?
You can send files through the code with single line like this:
<cfif isAuthorized>
<cfcontent file="/path/to/files/outside/of/web/root/Form.pdf" type="application/pdf" reset="true" />
</cfif>
ColdFusion FTW, right.
Please note that handling large files (say, 100MB+) may cause some problems, because files being pushed to RAM before sending. Looks like this is not correct any more, as Mike's answer explains.
Another option is to use content type like x-application if you want to force download.
UPD
You want to put this code into the file (let's say file.cfm) and use it for PDF links. Something like this:
Download file Xyz.pdf
file.cfm:
<!--- with trailing slash --->
<cfset basePath = "/path/to/files/outside/of/web/root/" />
<cfif isAuthorized AND StructKeyExists(url, "filename")
AND FileExists(basePath & url.filename)
AND isFile(basePath & url.filename)
AND GetDirectoryFromPath(basePath & url.filename) EQ basePath>
<cfcontent file="#basePath##url.filename#" type="application/pdf" reset="true" />
<cfelse>
<cfoutput>File not found, or you are not authorized to see it</cfoutput>
</cfif>
UPD2
Added GetDirectoryFromPath(basePath & url.filename) EQ basePath as easy and quick protection from the security issue mentioned.
Personally I usually use ID/database approach, though this answer was initially intended as simple guidance, not really compehensive solution.
You need to store your PDF's outside of your web realm.
So lets say the base of your web app is
/website/www
All http (web) requests are served from there.
/website/pdf
could be a path where all PDF's are stored. This path isn't accessible via URL as its not served by your web server.
Then in www
you have something like
downloadpdf.cfm?file=NameOfPDF.pdf
Which does your checks to ensure its an appropiate user and if so serves the document
<cfcontent type="application/pdf" file="/website/pdf/#url.file#" />
Using cfcontent, pre cf8, is a really bad idea, as it loads the entire file into memory before transmission. CF8 and later will actually stream from disk, which resolves the memory issue. However if you have large files, users on slow connections, and/or heavy downloads you still have to worry about thread starvation. Each download with cfcontent ties up a thread for the duration of the download.
Depending on your web server you might be able to route around this by using an x-sendfile extension. This allows you to send an http header with the path to a file outside of your web root, and have your web server handle sending the file, freeing up cf to do further work.
Here's an article by Ben Nadel about using mod_xsendfile on apache, http://www.bennadel.com/blog/2170-Streaming-Secure-Files-Efficiently-With-ColdFusion-And-MOD-XSendFile.htm and here's an equivalent IIS7 XSendFile plugin https://github.com/stakach/IIS-X-Sendfile-plugin
You might checkout the snippet of code for CFWheels SendFile() helper tag http://cfwheels.org/docs/1-1/function/sendfile
https://gist.github.com/1528113