Archive for the Flash Category
Users of Adobe products (i.e. almost all the web surfers) are in serious danger (well, not exactly breaking news).
Critical bugs in Flash Player and Acrobat, both allowing arbitrary remote code execution, are being exploited in the wild.
Adobe just released a Flash Update addressing the player vulnerability, which has been abused in real world attacks for more than 6 weeks. Notice that the FlashBlock work-around suggested by the iDefense bulletin is bogus: as we already clarified a few times, FlashBlock can’t be relied upon as a security defense. The only reliable means to protect yourself against Flash-based 0 day attacks like these are either disabling the Flash Player plugin globally, or using NoScript’s content blocking features to selectively enable only the Flash applets you trust.
Regarding the Acrobat flaw, Adobe announced that a patch won’t be available until March the 11th. In the meanwhile many sources, including Adobe itself, recommend to disable JavaScript execution in Acrobat’s options, but again the suggested work-around is not effective: disabling Acrobat’s JavaScript does not prevent the vulnerability from being exploited. As always, you should be very careful in opening PDF files you receive by email, and use NoScript to prevent automatic exploitation on the web: NoScript’s default deny policy applies to all the plugin content, indeed, including PDF.
13 Comments »
07
02
2009
Posted by: Giorgio in Flash, Mozilla, NoScript
As you probably know, plugins are external software components which the web browser delegates to render custom content inside web pages, and/or to play audio clips and potentially much more: they actually can do anything, since they’re executable code running inside the browser process, with the same privileges as their host. This can cause major security concerns, no doubt about that. They’ve accumulated lots of security issues of their own over the time, and the scriptable ones (like Flash or Java) are often used in combination with JavaScript to prepare memory for attacks working around protection features deployed by modern OSes. That’s why one of the major features of NoScript is blocking plugin content from untrusted web sites, and optionally from trusted too, in an easy “click to activate” fashion: this way you can considerably reduce your attack surface, while retaining the power of accessing plugin content on sites where you really need to.
Add-ons, in mozillaspeak, are a broader category, including plugins of course, but also themes (packages which can change your browser appearance, also called “skins” in other communities) and extensions. NoScript itself is an add-on, or more precisely an extension. Extensions are tiny applications developed with the same technologies which Firefox is made of (i.e. XUL, JavaScript, XPCOM and, possibly but rarely, C++) which upon installation get tightly integrated in the browser, extending (and hopefully enhancing) its functionality. They can access and modify practically any aspect of the browser, and are granted the same privileges as the browser. With great power comes great responsibility, and add-ons are obviously not immune of bugs which can compromise browser security.
There are some differences, though, between extensions and plugins in regard of security:
- Extensions which are found to be unsafe can be promptly disabled worldwide by Mozilla admins using a remote centralized mechanism. This is true for plugins too, but I’m very dubious that Mozilla would abruptly kill Flash (or even worse, Java) on all its users in reaction to a zero-day vulnerability disclosure…
- Extensions enjoy a safe and very effective update mechanism, which allow security updates to be deployed almost instantly. The same can’t be said for most, if not all, the most popular plugins.
- The vast majority of Firefox extensions are open sourced. Those hosted on AMO,
which is the only place where you can to safely install add-ons from* where Firefox sends you to safely install add-ons, must allow per-policy code reviews, therefore even in those rare cases where native executable code is included, this must comes with its sources, no matter the license. This allows manual screening against malicious extensions (all the hosted add-ons are also automatically scanned by anti-virus software anyway), or more focused security code reviews like the one Wladimir Palant performed recently.
Wladimir is also engaged in a laudable effort for educating extension developers to safer coding practices: whoever maintains or wants to develop a Firefox extension should subscribe his feed.
Coming to “Security Advisers”, Roger A. Grimes (a CPA, a CISSP, a CEH, a CHFI, a TICSA, and an MCSE: Security, which in plain English means more or less “security consultant with a strong Microsoft background”) recently wrote a serie of articles comparing security features of all the major browsers.
The one about Firefox contained, among others, a quite disturbing (for me at least) paragraph (emphasis is mine):
Although add-ons such as NoScript, and plug-ins such as Adobe Flash, bring many useful capabilities to Firefox, at the same time they come with problems and security issues of their own. Firefox has a built-in add-on manager that allows you to browse available extensions, install and uninstall them, and enable and disable them, but again, they can’t be enabled or disabled with per-site granularity.
So I decided to send Roger an email, sparking a pretty intense exchange (in the meanwhile, I was implementing PoC X-Frame-Options compatibility for Firefox with my left hand).
Yesterday I noticed he published a synthesis of our discussion. Even though he cut some logic passages, making our reasoning a bit hard to follow, I have been positively impressed by his openness and I’d like to rectify just two little things:
- Roger introduces his report of our thread with these words:
I indicated that browser add-ons (or plug-ins) could bring additional risk to a browser. One browser add-on provider, Giorgio Maone of Firefox’s NoScript, wrote me to strongly disagree.
As this very post of mine demonstrates, I couldn’t and didn’t disagree on the concept “that browser add-ons could bring additional risk to a browser“. But I was rather surprised (and, honestly, pissed off) about his suggestive exemplification choices.
- In an original message of mine, I tried to explain my objection this way:
You would never dare to say “Mail servers and Web servers, such as qmail and IIS, which come with problems and security issues of their own…”
I choose qmail for my example because of its almost immaculate security records: should you pick a single product to illustrate mail server security risks, you’d bash Sendmail with its several documented vulnerabilities, rather than DJB’s impervious creature. However the article inexplicably morphed “qmail” into GMail, making my point quite obscure (given that GMail is not even a proper mail server, nor exactly a security champion).
That said, I appreciate Roger’s transparency and I hope we’ll have chances for new constructive discussions.
* Note: JJ Barton correctly made me notice that sites different than AMO can adopt the same hosting security policies (automatic update over a SSL channel, which by the way is required by the Mozilla browser toolkit itself, and possibly blacklisting of unsafe versions), e.g. GetFirebug.com for the Firebug extension. However AMO is the place where you’re automatically directed by Firefox itself when you look for an add-on, so stressing its security features was very important.
16 Comments »
SecTheory published a paper by Robert “RSnake” Hansen about Browser Power Consumption. Dan Goodin reports about it under the rather funny title Study spanks Adobe Flash for abuses of power (ehy Dan, why just Adobe? what about Microsoft and Sun?). PC World has an article as well, interviewing a Pacific Gas and Electric representative.
The green juice: you can reduce your PC’s power consumption by 25% when you browse the web using Firefox with NoScript and AdBlock Plus. Quite obvious, since JavaScript, Flash, Java, Silverlight and active content in general are major CPU-drainers, compared to static pages. By allowing them just when and where they’re needed, the way NoScript works, you do the equivalent of closing the tap when you’re brushing your teeth or turn off the light when you exit a room.
Of course it’s just a drop in the ocean, but I like to believe I’m helping Gaia a bit and enabling others to do the same :)
Update
Commenter Arthur reminded me that, even if you didn’t give a damn about environment health, as a mobile user you surely value your battery life and you’ve got yet another good reason for using NoScript. And did I mention you can use NoScript on the Fennec mobile browser now?
6 Comments »
Finally NoScript 1.8.2.1 is out, featuring the announced new anti-clickjacking countermeasures enabled by default, independent from IFRAME and plugin content blocking settings.
The most specific and ambitious is called ClearClick: whenever you click or otherwise interact, through your mouse or your keyboard, with an embedded element which is partially obstructed, transparent or otherwise disguised, NoScript prevents the interaction from completing and reveals you the real thing in “clear”. At that point you can evaluate if the click target was actually the intended one, and decide if keeping it locked or unlock it for free interaction. This comes quite handy now that more dangerous usages of clickjacking are being disclosed, such as enabling your microphone or your webcam behind your back to spy you through the interwebs.
As you already know if you read my first clickjacking article, an old and benign clickjacking example is NoScript’s “Install Now” orange button, which overlays the green one on addons.mozilla.org to work-around the installation security warning. If you click it with ClearClick enabled, now you get warned about something sneaky going on.
I do not need to change my button yet, because NoScript 1.8.2.1 ships with ClearClick enabled on untrusted (non whitelisted) parent pages only, while the whitelist status of the embedding is irrelevant. This gives a good balance between effectiveness and usability, since the attacker in a clickjacking attack is always the parent. If you want to get the warning on noscript.net and on the other sites you trust, you need to flag the second checkbox on NoScript Options|Plugins|ClearClick protection on pages… [x] untrusted [x] trusted. I recommend to flag it anyway and report any usability issue, because this feature so far seems quiet and unobtrusive enough to justify my temptation of enabling everywhere (trusted + untrusted) by default on next stable release, but it must get a lot of testing from you first.
Update
NoScript 1.8.4 and above ship with ClearClick enabled on both untrusted and trusted sites. It works everywhere, even if you’ve got scripts globally allowed. And yes, at that point I had to change noscript.net install button, therefore if you want a PoC you need to look elsewhere.
Other clickjacking-related features included in this release are:
- Opaque embedded objects: plugin content and frames are forcibly made opaque and get styled with “overflow: auto” (i.e. get scrollbars if their inner size exceed their viewport) on untrusted pages.
- Frame Break Emulation: if a framed page which is not allowed to run JavaScript contains a “frame busting” script similar to
<script>if (top != self) top.location = location</script>
, the intention of the page author is honored by NoScript, i.e. the page replaces the topmost document. You can control this feature toggling the noscript.emulateFrameBreak about:config preference.
- Some usability and effectiveness improvements in frame management, making the Forbid IFRAMEs option more suitable for general usage.
I hope to find some time during this week to write another post, diving through the technical details behind my ClearClick implementation: a fairy tale about a very simple and hopeful idea (unconventional <canvas> usage) fighting against an army of quirks and mundane details. In the meanwhile, many thanks to Sirdarckcat, RSnake, Michal Zalewski and Matt Mastracci for discussion, testing and inspiration.
72 Comments »
|
