[skuzins]

Chrome's sandboxing is conceptually more secure than IE's, and NACL is more secure than sandboxed ActiveX. The key difference in both cases is granularity.

Chrome sandboxes each tab individually, whereas IE runs all tabs in the same sandbox. It's true that in both cases a malicious website could not cause much damage to the OS, but as more stuff moves into the browser it becomes more important that a malicious web app cannot mess with other web apps (tabs) that are open.

If a malicious website gains control over the IE sandbox, it has access to all web sessions within the sandbox. This is not true for Chrome.

Chrome, like IE, uses OS mechanisms for its sandboxing on Windows, most importantly restricted tokens. These have been around since Windows 2000 and are more powerful than the one dimensional integrity level introduced with Vista.

NACL is two steps ahead of ActiveX with regards to security. An ActiveX control running in the IE sandbox has immediate access to the whole sandbox (which includes all running tabs). Because of this, one would never run an untrusted ActiveX control, period. Hence the prompts and signature checks.

NACL on the other hand has two layers of defense, and each one would conceptually be sufficient to run untrusted content. The first layer is the native client sandbox (with the verified machine code etc.). The second layer is the per-tab Chrome sandbox described above. So even if a native client app breaks out of the native client sandbox, it would then have to break out of its tab's Chrome sandbox to do any damage at all.

[briansmith]

IE8 does sometimes put multiple tabs in one process, but not all tabs are in the same process. I think Microsoft should move to one-process-per-tab too; if Chrome can do it without any negative performance impact (AFAICT), so should IE. But, I'm not sure the rest of what Chrome does would be useful in IE. Microsoft wants to keep the security enforcement in the operating system so that all native applications can benefit from it. Google is happy to have lots of security enforcement in Chrome itself because it doesn't really care about the security of anything other than Chrome, and it cares about platforms that don't have the security features that Windows has.

In particular, one thing that's strange about NaCL is that plugin processes have stronger security than Chrome itself (unless Chrome is being built with the same or similar NaCL toolchain). In Microsoft's design, plugins are protected equally with the IE tab processes themselves, which seems very sensible to me, considering all the untrusted content that the browser itself has to interpret.

I would still like to know, theoretically, what Chrome's design stops that cannot be stopped using IE8's design, modified to have one tab per process.

[skuzins]

IE8 does sometimes put multiple tabs in one process, but not all tabs are in the same process. I think Microsoft should move to one-process-per-tab too;

The problem is that all these processes run in the same sandbox (at the integrity level "Low"), so they are not protected from each other.

But, I'm not sure the rest of what Chrome does would be useful in IE

Again, like IE, Chrome itself uses OS mechanisms for the sandboxing.

In particular, one thing that's strange about NaCL is that plugin processes have stronger security than Chrome itself

This differentiation seems reasonable because Chrome itself is considered trusted code, whereas these plugins aren't.

I would still like to know, theoretically, what Chrome's design stops that cannot be stopped using IE8's design, modified to have one tab per process.

Since IE has one sandbox for all processes, one compromised tab could affect other tabs. Not so in Chrome. If IE switched to one process per tab and one sandbox per process, things would be more similar, but NACL in a Chrome sandbox would still be more secure than ActiveX in an IE sandbox because of NACL's additional layer of security. A NACL plugin would need to exploit weaknesses in both NACL and the Chrome sandbox in order to do any damage.