I'd like to only allow users to be able to click a link once, like this one:
http://www.blah.com/download.php?file=zFZpj4b2AkEFz%2B3O
Each user has an e-mail sent with a unique link and when they click on it I'd like to set a cookie on the SERVER so I know to reject that link's access again.
Any ideas welcome.
Thank you.
Blocking duplicate download could cause issues (especially with internet explorers file blocker that causes a page refresh).
Cookies are the wrong answer because all the user has to do is use a different browser/machine or clear their cookies to redownload.
If you are desperate to do this how about
On the file system create a symbolic link to the real file and name the link the same as the key.
On processing the page request:
validate the url string (to avoid path jumping etc)
Check for the existence of this link, if it doesn't exist link is invalid/expired so show error
Otherwise, Copy file to response
Delete link
On download.php check if the a cookie like AlreadyAccessed exists and if it exists deny the download otherwise start the download of file and set cookie. That's it
Cookies are stored client-side, not server-side, so that's not the right option. If a user deletes your site's cookies, he'd be able to circumvent any check that is based on cookie existence/value.
You could create a file on the server with a specific name when you send the link, and remove it once it's been accessed. If someone tries to access the link a second time, the "flag" file will not exist and you'll know it's a repeat (or invalid) link.
(Would be better with a database though, file-based checks are hard to do in a non-racy manner.)
Related
My question seems to be similar to others here in SO, I have try a few but it doesn't seem to work in my case...
I have develop a site in which you have to fill up a form and then it returns a PDF file that you can download or print, this file is saved so you can retrieve it later
public_html
|_index.php
|_<files>
| |_file_001.pdf
| |_file_002.pdf
|_<asstes> ....etc
that is how my files and folders look on the server, anyone can easily guess other files, .com/folder/file_00X.pdf, where X can be change for any other number and get access to the file... the user after finish with the form the script returns a url .com/file/file_001.pdf so he/she can click on it to download...
a year ago I did something similar an script to generate PDF's but in that case the user needed the email and a code that was sent via email in order to generate the PDF and the PDF's are generated on demand not saved like in this case...
Is there a way to protect this files as they are right now?
or, do I have to make it a little bit more hard to guess?
something like.
.com/files/HASH(MD5)(MICROTIME)/file_(MICROTIME)_001.pdf
and save the file and folder name in the DB for easy access via admin panel, the user will have to get the full URL via email...
Any ideas would be greatly appreciated.
For full security i would move the PDFs out of the public folder and have ascript in charge of delivering the content. If the form is filled correctly, you can generate a temporary hash and store that hash and the pdf path in the database. That way the user will have access to the file as a link through the retriever script, but you will control for how long he will have that link available.
Imagine the temporary link being http://yourdomain/get_pdf/THIS_IS_THE_HASH
Move the PDF's to some non-public folder (that your web server has access to but the public does not). Or you can use .htaccess to restrict access to the pdf's in their current location.
Write a php script that returns the correct pdf based on some passed in http variable.
You can secure/restrict this any way that you want to.
For example, one answer suggested using a temporary hash.
Other options for restricting access:
Store in the user's session that they submit the form and have a download pending, that way no one could direct link.
Check the referrer header. If it is a direct request then do not serve the file.
Here is a code example using the last option:
$hash_or_other_identifier = $_REQUEST["SomeVariable"];
if (!$_SERVER["HTTP_REFERER"])
{
//dont serve the file
} else {
//lookup the file path using the $hash_or_other_identifier
$pdfFile = somelogic($hash_or_other_identifier);
//serve the correct pdf
die(file_get_contents($pdfFile));
}
I don't even think that keeping the file name secret is a very big deal if all you are worried about is people typing it into the URL bar because you can simply check if it is a direct link or not. If you are also worried about bots or clever people who will create a link that points to your file so it looks like a referrer, then you will need to add stricter checks. For example, you can verify that the referrer is your own site. Of course headers can be spoofed so it all just depends how bulletproof it needs to be.
The url would be something like: http://yourdomain/pdf?SomeVariable=12345
However, you don't have to use an http variable. You can also use a url fragment with the same result, eg: http://yourdomain/pdf/12345
General guidelines:
File is not in the directory that's accessible via HTTP
Use a database or any other storage to link up file location with an identifier (an auto incremented number, guid, hash, whatever you deem fit). The location of the file could be in the server's file system or on a shared network location etc.
Instead of hashes, it's also practical to encrypt the ID generated by the database, base64 encode it and provide it back - that makes it nearly impossible to guess the valid string that one needs to send back in order to refer to a file
Use a PHP script that delivers the file if user authentication passes (in case you need authenticated users to be able to retrieve the file)
I want to mask a file URL on my site so that it can be accessed, but they can't find the direct URL of the file, even if the view the HTML source code. I don't know if it is possible with php, but please help me. Anything will do.
If I understand your question correctly, you want to avoid "deep linking", i.e. someone extracting the file URL from your page and using it elsewhere.
This can not directly be done, as the information is needed by the browser to access the file, and a determined attacker will quite easily be able to extract it.
There is a workaround though: Make this URL dynamic.
Place file outside the publically accessible web root
When delivering the HTML page from PHP, create a download token, that has the file path, an expiry time (and maybe other factors such as a session ID, a referrer URL, etc ...) cryptographically secured (i.e. hash it together with a server-known secret)
Deliver a link to a download script, not the file iself
inside the download script, verify the parameters and the hash, exit with a 304 (or maybe 404) if wrong
if verification passes, simply deliver the file
This will protect you from deeplinking in that an attacker will be able to extract an URL, that loses its validity after your expiry time. If you use an AJAX request to create the download token immediately before starting the download, you can make this quite short (few seconds)
You can't.
The browser has to know the URL to request the file from.
The browser is under the control of the user.
Any information you give to the browser, you also give to the user.
I have a url in this format: "sitename.com/folder/file.php". How do I make it a "sitename.com/randomhash" or "sitename.com/folder/randomhash" format?
I know I can use a GET & Switch system but I need the name to be unique and I need to be able to change it on the fly.
I don't really understand what your point is, but if you don't want you're visitors to know where your php-files are stored, I would recommend reading this:
Tutorial for URL handling in PHP
If you are having a website where people can download stuff, and you don't want people hotlinking your files, you could do the following steps (i'm not writing the code, I'm just going to give you a general idea):
People come to your website.
Person clicks on link because they want to download that particular file.
Person comes on page, where you have the opportunity to set a cookie with a random hash.
Simultaneously you put a value in a database, with the same hash and the filepath of the file they want to download.
On this page, they have to click "DOWNLOAD NOW!", where they are redirected to download.php.
In download.php you read the cookie, then match that with the database and get the filepath.
With the right php-headers, you can force download.php to download the file.
Important in this situation is that you set your settings of Apache (or whatever server you have) that downloading is not allowed unless 'localhost' is requesting it.
I want my files to be secure in my web server. Only authenticated users to access those files should be able to access those files. I thought of storing files in database as "Long BLOB" but it supports only upto 2MB of data. The file size may exceed beyond 50MB. is there any other better way to secure the files? please help me.thanks in advance.
Don't store them in a database. Put them in your web directory and secure them using .htaccess.
If you want to authenticate via other means, then store the files in a directory that isn't web-accessible but is readable by the user php runs as.
Discussion
If you opt to keep high value downloadable content files directly on the filesystem, the best thing to do is to keep them outside of the webroot.
Then, your application will have to solve the problem of creating URLs (url encoding when necessary) for content (PDF's, Word Docs, Songs, etc..).
Generally, this can be achieved by using a query to retrieve the file path, then using the file path to send content to the user (with header() etc ..) when he or she clicks on an anchor (all of this without the user ever seeing the true, server side file path).
If you do not want user A sharing URLs for high value downloadable content to user B, then your application must somehow make the links exclusively tied to user A. What can be done? Where should I start?
Obviously, you want to make sure user A is logged in during a session before he or she can download a file. What is not so obvious is how to prevent a logged in user B from using a URL sent from user A (to user B) to download A's digital content.
Using $_SESSION to store the logged in user's ID (numerical, or string) and making that part of the eventual query (assuming content is tied to user purchases or something) will prevent a logged in user B from downloading things they have not purchased, but you will still incur the resource hit for processing the SQL empty set for items they have not purchased. This sounds like a good step two.
What about step one? Is there something that can prevent the need to do a query to begin with?
Well, let us see. In HTML forms, one might use a XSRF token in a hidden field to verify that a submitted form actually originated from the web server that receives the POST/GET request. One token is used for the entire form.
Given a page of user specific things to download (anchors), one could embed a single token (the same token, but different per page request) into each anchor's href attribute in the form of a query string parameter and store a copy of this token in $_SESSION.
Now, when a logged in user B attempts to use a logged in user A's shared URL, the whole thing fails because user A and user B have different sessions (or, no session at all), and thus different tokens. In other words, "My link is the same as yours, but different." Anchors would be tied to the session, not just to the page, user, or content.
With that system in place, PHP can determine if a request for content is valid without getting the database involved (by comparing the submitted token to the one in $_SESSION). What is more, a time limit can be established in $_SESSION to limit the duration/lifetime of a valid XSRF token. Just use the time() function and basic math. Sixty minutes might be an ideal token lifetime for an anchor in this situation. Have the user login again if the token for a clicked anchor has expired.
Summary
If you use files on a filesystem and store the paths in the database, make sure you do the following (at minimum), too.
Apply proper file permissions to your content directory (outside of webroot).
Use random names for uploaded files.
Check for duplicate file names before saving a file from an upload.
Only logged in users should be able to download high value content.
Have an effective $_SESSION system that deters session fixation.
Make URLs for high value downloadable content unique per page by using hashed XSRF tokens.
XSRF tokens cover more scenarios when they have a terminal life time.
Make SQL queries for user content based on the logged in user's ID, not the product exclusively.
Filter and validate all user input.
Use prepared statements with SQL queries.
A few options come to mind.
If you are using Apache you can use htaccess to password protect directories. (first googled link : http://www.javascriptkit.com/howto/htaccess3.shtml)
or
Store the files above the web server.
Create a script in php that will allow authorised users to access them.
If you want to do it Via FTP, and you are running cpanel you may be able to create new ftp accounts. check yourdomain.com/cpanel to determine if you have it installed.
Storing files in DB is very bad practice. Very good practice to store only information about file. Name, extension. Files save on server like $id.$ext. It will be a good architecture. And when user download file, he take file with name in DB.Sorry for my english.
The best way is to store the file reference in Database. The file itself will be stored in the server filesystem. The complexity of this is making sure there is reference integrity between the database file reference and the existing file in the server filesystem. Some database such as sql server 2008 have feature that maintain the integrity of the file references to the actual file itself.
Other than that securing the file itself in the server depends on the OS where permissions can be configured to the specific folder where the file reside.
If the files are purely static you could use read-only or WORM media to store the data files or indeed run the complete web server from a "LiveCD". It's certainly not suited to everyone's needs but for limited cases where the integrity of the data is paramount it works.
Downloadable files can be stored in htaccess protected folder/s. A script like the one below can be used to generate dynamic links for downloadable files.
for ex. Secure download links. http://codecanyon.net/item/secure-download-links/309295
there is a page that i need to post a password to it and then i get a file to download.
the post goes to the same page address its loads again and pop up the download manager (download starts automatically).
now i want to do the same but in curl, i posted the data to the url and then its sends me the file back but i don't want my script to download the whole file i want only to get a link to download it by myself.
how can i do that?
Actually, you most probably can't. Such password protected download system usually checks either cookies or browser / environment based variables. Getting the link itself shouldn't be problem, however you could not use it outside this generator's scope anyway.
firstly you need to post that password with curl assuming "on specific form. the form will take you to the downloading page" now you need to use regex (regular expressions).
filter the data you want then save it on other variable to re-use it.
There is for sure a redirection after you hit 1st page with POST. Look for that redirection with curl and read http response headers: Content-Location or Location or even Refresh
To prevent the automatic download you have to set the curl opt to not follow redirects. I can't remember the exact command but curl by default will follow auto refreshes and URL redirects, which happen in split seconds so humans don't actually see it happening.
I kinda don't understand what you really want to do, but if you just want a link then have the php script perform the entire curl post and everything when they click it. Doesn't matter what the web server will require a password before access to a file, you can't skip that step.