If we have a web page that able to read or delete file (based on name) inside certain folder, for example: 'public/upload/', what kind of filtering we must use to prevent security issues?
For example in Ruby/Sinatra:
file_name = params[:file_name]
base_dir = 'public/upload/'
# prevent user from entering ../../../../../etc/passwd or any other things
file_name.gsub!('../','')
File.delete "#{base_dir}/#{file_name}"
Is it enough?
This kind of filtering is always error prone. However, something that could work, but which I cannot say is bulletproof, would be this:
Preventing Directory Traversal in PHP but allowing paths
Ruby has something like php's "realpath" afaik.
OWASP also has bit on how to prevent path traversal:
https://www.owasp.org/index.php/File_System#Path_traversal
Along with examples of how path traversal can be exploited:
https://www.owasp.org/index.php/Path_Traversal
Related
TLDR
I need to get paths to system directories like "Screenshots":
On an English system. I can just use this one:
C:/Users/User/Pictures/Screenshots
How do I get the path to "Screenshots" directory on a non-English system?
C:/Users/User/Pictures/[NAME]
Description
I have a file manager app, it displays system directories and loads them on click.
The app can run system commands via Powershell and use Node.js (preferred)
Problem
The problem is, it only works if the system has English system language.
Currently, to resolve the "Screenshots" directory path, the app simply joins the User directory with the word "Screenshots"
const pictures = electronRemote.app.getPath('pictures')
const screenshots = PATH.join(pictures, 'Screenshots')
link to the line in code
Expectedly, the C:/Users/User/Screenshots path only exists on English systems.
One way to solve this is to use short names, at least on Windows, I know that system directories have short names like SCREEN~1 and WALLPA~1 for Screenshots and Wallpapers directories, but if I use these names the paths will look like this:
C:/Users/User/SCREEN~1 instead of C:/Users/User/Screenshots throughout the app.
And even if I were to run these paths through a function to convert it to readable name, how would I know which word to replace it with? I need to get the name in the system's language.
Are these translations stored somewhere on the system? Can I just retrieve the translated directory name and use that in the code above?
Question
How do I make it to get / resolve the actual path of system directories like Screenshots and Wallpapers, independently of system locale?
If you know how to do it, could you please suggest the solution for all platforms (Win, Mac, Linux)?
Should I just use the short names like SCREEN~1 and then automatically replace all the occurrences in UI and also filter all paths through a function that replaces this short name with the actual path throughout the whole app? Seems like a lot of work, this approach
Is there a way to construct a filepath that links to the Documents folder of the active user. So instead of C:\Users\User\Documents\ something like C:\Active_User\Documents\
ps. I try to make use of this in KNIME.
The file chooser elements in KNIME understand a URL in the form of "knime://knime.workflow" which accesses the current workflow location regardless of higher directory path.
You could also use a Java Variable Edit to get the username in Java, which you use to create a string that can be used by the File Reader (or other node) as a flow variable.
It depends on what you're trying to achieve.
You can use
C:\Users\%USERNAME%\Documents
which will use the environment variable %USERNAME% (= current user).
In C#/.NET you can use Environment.SpecialFolder.MyDocuments like this:
Console.WriteLine("GetFolderPath: {0}",
Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments));
In Java System.getProperty("user.home"); should give you the right base diretory to start with.
I have a Java Web App running on Tomcat on which I'm supposed to exploit Path traversal vulnerability. There is a section (in the App) at which I can upload a .zip file, which gets extracted in the server's /tmp directory. The content of the .zip file is not being checked, so basically I could put anything in it. I tried putting a .jsp file in it and it extracts perfectly. My problem is that I don't know how to reach this file as a "normal" user from browser. I tried entering ../../../tmp/somepage.jsp in the address bar, but Tomcat just strips the ../ and gives me http://localhost:8080/tmp/ resource not available.
Ideal would be if I could somehow encode ../ in the path of somepage.jsp so that it gets extracted in the web riot directory of the Web App. Is this possible? Are there maybe any escape sequences that would translate to ../ after extracting?
Any ideas would be highly appreciated.
Note: This is a school project in a Security course where I'm supposed to locate vulnerabilities and correct them. Not trying to harm anyone...
Sorry about the downvotes. Security is very important, and should be taught.
Do you pass in the file name to be used?
The check that the server does is probably something something like If location starts with "/tmp" then allow it. So what you want to do is pass `/tmp/../home/webapp/"?
Another idea would be to see if you could craft a zip file that would result in the contents being moved up - like if you set "../" in the filename inside the zip, what would happen? You might need to manually modify things if your zip tools don't allow it.
To protect against this kind of vulnerability you are looking for something like this:
String somedirectory = "c:/fixed_directory/";
String file = request.getParameter("file");
if(file.indexOf(".")>-1)
{
//if it contains a ., disallow
out.print("stop trying to hack");
return;
}
else
{
//load specified file and print to screen
loadfile(somedirectory+file+".txt");
///.....
}
If you just were to pass the variable "file" to your loadfile function without checking, then someone could make a link to load any file they want. See https://www.owasp.org/index.php/Path_Traversal
I am writing a small command line utility. It should hopefully be able to run on OSX, UNIX and Linux.
It needs to save a few preferences somewhere, like in a small YAML config file.
Where would one save such a file?
Language: Python 2.7
OS: *nix
Commonly, these files go somewhere like ~/.rc (eg: ~/.hgrc). This could be the path to a file, or to a directory if you need lots of configuration settings.
For a nice description see http://www.linuxtopia.org/online_books/programming_books/art_of_unix_programming/ch10s03.html
I would avoid putting the file in the ~ directory only because it has gotten totally flooded with crap. The recent trend, at least on ubuntu, is to use ~/.config/<appname>/ for whatever dot files you need. I really like that convention.
If your application is named "someapp" you save the configuration in a file such as $HOME/.someapp. You can give the config file an extension if you like. If you think your app may have more than one config file you can use the directory $HOME/.someapp and create regular-named (not hidden) files in there.
Many cross-platform tools use the same path on OS X as on linux (and other POSIX/non-Windows platforms). The main advantage of using the POSIX locations isn't saving a few lines of code, but saving the need for Mac-specific instructions, and allowing Mac users to get help from the linux users in the community (without any need to translate their suggestions).
The other alternative is to put them in the "Mac-friendly" locations under ~/Library instead. The main advantage of using the Mac locations is basically "Apple says so"—unless you plan to sandbox your code, in which case the main advantage is that you can do so.
If you choose to use the Library locations, you should read About the OS X File System and OS X Library Directory Details in the File System Programming Guide, but here's the short version:
Almost everything: Create a subdirectory with your app's name or bundle ID (unless you're going out of your way to set a bundle ID, you'll get org.python.python, which you don't want…) under ~/Library/Application Support. Ideally you should use APIs like -[NSFileManager URLForDirectory:inDomain:appropriateForURL:create:error:] to get the path; if not, you have to deal with things like localization, sandbox containers, etc. manually.
Anything that can be easily re-created (so it doesn't need to be backed up, migrated, etc.): An identically-named subdirectory of ~/Library/Caches.
Preferences: Use the NSUserDefaults or CFPreferences APIs instead. If you use your own format, the "old" way of doing things is to create a subdirectory under ~/Library/Preferences named with your app's name or bundle ID, and put your files in that. Apple no longer recommends that, but doesn't really recommend an alternative (short of "use CFPreferences, damnit!"); many apps (e.g., Aquamacs) still do it the old way, but others instead pretend they're not preferences and store them under Application Support.
In Python, this works as follows (leaving out the error handling, and assuming you're going by name instead of setting a bundle ID for yourself):
from Foundation import *
fm = NSFileManager.defaultManager()
appsupport = (fm.URLForDirectory_inDomain_appropriateForURL_create_error_(
NSApplicationSupportDirectory, NSUserDomainMask, None, True, None)[0].
URLByAppendingPathComponent_isDirectory_(
appname, True))
caches = (fm.URLForDirectory_inDomain_appropriateForURL_create_error_(
NSCachesDirectory, NSUserDomainMask, None, True, None)[0].
URLByAppendingPathComponent_isDirectory_(
appname, True))
prefs = NSUserDefaults.persistentDomainForName_(appname)
I recently coded something where it wasn't known if the end code would reside in a subdomain (http://user.domain.com/) or in a subdomain (http://domain.com/user), and I was lost as to the best practice for these unknown scenarios. I could thinks of a couple:
Use absolute paths (/css/styles.css) and modrewrite if it ends up being /user
Have a settings file and declare a variable with the path (<? php echo $domain . "/css/styles" ?>)
Use relative paths (../css/styles.css).
What is the best way to handle this?
If there is any question about where something might be deployed, I would avoid absolute paths whenever possible, and if you must use them, make sure to construct them using the data in the $_SERVER superglobal. The value $_SERVER['PHP_SELF'] will contain the path and filename to the currently executing script, and you can then extract the path using something like:
$path = dirname($_SERVER['PHP_SELF']);
Likewise, the value $_SERVER['HTTP_HOST'] will contain the current host, and from those two together you can build the path to wherever you are. If you're using HTTPS you may also need to check the protocol in $_SERVER['HTTPS'].
With that said, it is still best to use relative paths and a simple file and directory structure whenever possible, since it makes everything more portable and easier to read. If, as in your example, you find yourself doing a lot of ../css/styles.css then you may want to reconsider how things are structured.
Mix of 2 and 3. Use paths relative to a set variable.