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Flash Vulnerability Found, Adobe Says No Fix Forthcoming
An anonymous reader writes "Security researchers at Foreground Security have found an issue with Adobe Flash. Any site that allows files to be uploaded could be vulnerable to this issue (whether they serve Flash or not!). Adobe has said that no easy fix exists and no patch is forthcoming. Adobe puts the responsibility on the website administrators themselves to fix this problem, but they themselves seem to be vulnerable to these problems. Every user with Flash installed is vulnerable to this new type of attack and — until IT administrators fix their sites — will continue to be."
Didn't really read the article, did you?
Uploading the swf as an avatar is just the beginning. You can also overload ZIP files, which also includes .docx, making perfectly legal documents that also are executable flash objects. Also, many server-side validation libraries apparently will also not catch properly malformed (if such a thing is possible) pdfs, mp3s, etc.
Ironically, all that email antivirus that require you to zip up your files does no good here... a overloaded zip file can be used to compromise webmail clients (like gmail, as in the example).
Flash's security policy is severely broken. I'd call this a pretty big deal.
You, sir, are entitled to the Arrogant Uninformed Derogatory Comment of The Day Award. Here's why, a quote from TFA:
It gets worse. Uploading a SWF with a .jpg extension, or a forged content-type header will get you a long way, but what if you can upload perfectly valid files with malicious content? Remember GIFAR? The basic premise is this: Overload a GIF file with a JAR archive. Specifically, the ZIP file format can be appended to any binary file and still be valid. The GIF format, in turn, can have any binary file appended to it. The JAR archive, being essentially a ZIP file, can be combined with a GIF image to create a a file that is both a valid image and a perfectly valid JAR archive. While SWF files cannot be appended to other formats, the inverse of the GIFAR exploit works- any file format in the ZIP family can have a SWF file prepended to it. This means that ZIP archives, self-extracting executables, Microsoft Office Open XML documents, XPI files, and, if you want to be ridiculous, even JAR files can all be crafted to contain executable SWFs. Additionally, if you don't care too much about compliance with standards (and what attacker does?), many server-side content validation libraries will also allow malformed PDFs, MP3s, and other media formats, so long as you are careful not to mangle them too much. This content overloading technique has countless variations, but the end result is always the same: no matter how good your validation routines, you simply cannot trust user-supplied content.
Short of rewriting everything that has anything to do with several popular formats, you're out of luck.
How, you do ask, is such a prepared file going to be uploaded? A worm that intercepts uploads in the browser, for example. I was able to come up with this in two minuttes, I'm sure that any self-respecting blackhat hacker will as well.
This is Slashdot. Common sense is futile. You will be modded down.
Flash files can also be loaded by embedding them in an HTML page with attributes that say "content-type='application-x-shockwave-flash'" or something like that, regardless of extension or the content-type header given by the server. The server may think it's a zip file, but your browser can still be convinced to run it as flash.
So, I drop a malicious .docx on vulnerable site, create my own web page that embeds the object, and get you to visit that page. presto, you're pwned.
It would probably be more accurate to say that websites (not servers) are vulnerable to such an attack. After all, unless I've misread TFA, no code is actually being executed server side. Instead, what's happening is that any SWF's posted to a publicly-accessible location are being served under the server's domain and therefore any scripts in the SWF will execute with rights to access that domain. There's nothing the SWF can do through scripting that a visitor can't do directly, so depending on how you look at it you could say the server itself isn't vulnerable to this, but the website and the clients are.
"In prison you just have to shut your eyes and take it. Here you have to shut your eyes and give it."
There is no vulnerability if the clients don't have flash installed.
It's a client-side vulnerability.
Given flash's popularity, webmasters should understand the risk and block uploads of .SWFs and application/x-flash
However, expecting webmasters to scan .jpeg uploads of declared type image/jpeg or declared application/octet-stream uploads to determine if flash might execute them, when they are intended to be simple downloads or image displays is way over the line...
Especially if an attacker can construct an image file that is a valid image, but flash will pick up and execute......
These Flash cookies are hidden from the user, and require special tools [fightidentitytheft.com] to remove.
Not to speak to any of your other points, but this isn't true. The Flash cookies are simply in your filesystem somewhere and can be deleted like any other files. (Where they are exactly depends on your browser and OS, but they're still just regular files.)
You can't delete them from within the browser without addons or plugins (in other words, the Flash plugin itself does not let you do this -- at least, not without manually setting the allowed disk space to 0 for every single website, which is impractical at best), but unless you consider bash or Windows Explorer to be "special tools," it's not exactly a heinous task.
"Destroy science and religion. Science would re-emerge exactly the same; but not religion." - Penn Jillette, paraphrased
It doesn't quite work like that. Most browsers don't look at magic bytes to try to guess the content of a file, nor do they look at the file extension (since there's no need for anything on the web to actually have a file extension at all); the content-type header is sent by the server for that purpose. (Internet Explorer is one exception to the "most browsers" rule.).
If you click on a link to a .zip file with SWF at the start, the server will (probably) say it's content-type is application/zip or similar, and the browser will do whatever it's configured to do for that kind of content. If the server says its content-type is image/jpeg, the browser will try to interpret it as a JPEG image (and probably fail, resulting in an error being displayed). The browser doesn't try to guess what the content is (unless it's MSIE).
However, you don't normally run a Flash object by clicking on a link to it. When you link to/embed an external resource within HTML, you can specify the content-type within the HTML. Think <link rel="stylesheet" href="..." type="text/css"> for including a stylesheet. This tells the browser not just where it is, but also what it is. This effectively overrides whatever content-type the server sends. It's very often used with <object> or <embed> tags to give the browser an idea of what the object is so it knows whether or not it can handle it before it requests it. It also enables you to put content on servers which don't have a mime-type configured for that file extension and still have them work.
As such, you can embed in a Flash object into a page, referencing an object with a .zip extension, and the browser will ignore the content-type as supplied by the server because it's already been told that it's a Flash object. Therefore, it'll be executed by the Flash plugin. If you also had a normal direct link to the file on the same page and a user clicked on it, it'd be opened in their archive manager, because the browser would be relying on the content-type header sent by the server.
You missed the point. Flash is not equally bad as JavaScript, it's far worse.
Suppose I'm an attacker, and I upload a malicious javascript file to www.victimsite.example. I then reference it in a site I control www.seemingly-innocuous.example, the javascript file runs in the www.seemingly-innocuous.example domain sandbox. Even though the file was loaded from www.victimsite.example, it can't actually access anything on the victim's site. In order for that to happen I would have to also upload a malicious html document to www.victimsite.example, and convince unwary surfers to visit this new page.
Now I decide to switch to flash. I upload a malicious SWF to www.victimsite.example, and embed it into a page at www.seemingly-innocuous.example. Unlike the JavaScript example, my malicious SWF now runs in the www.victimsite.example domain security sandbox, and can make any requests it wants to the victimsite.example domain without the visitor to my seemingly innocuous domain being any the wiser.
It is a big deal, and it is nothing at all like JavaScript. But it's also not remotely new. I'm having a hard time finding anything in this article that hasn't been widely know for some time now. It even mentions attacks that have been going on for years.
If I don't put anything here, will anyone recognize me anymore?