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by trunnell 6108 days ago
although it's not clear why this isn't a huge vector to cause all sorts of havoc.

First the larger question: Is the Silverlight sandbox safe? The Silverlight CoreCLR security model is a simplified version of the full CLR security model [1].

Some callouts:

- C# "unsafe" code blocks, which let you access raw pointers, are not allowed.

- P/Invoke and COM Interop are not allowed.

- There are whole categories of the .NET class library that have been removed, a notable example being local file access. Silverlight is not like Adobe AIR, which gives you all sorts of native APIs.

- Socket communications are restricted by default to the original host from which the Silverlight app was downloaded. Cross-domain access can be granted by supplying either a Flash policy file or a Silverlight-native policy file. [2]

Therefore, to say whether this could be used for DDOS attacks on other hosts, we need to look at the network access policy file. Here it is: http://www.wiki-os.org/clientaccesspolicy.xml . As configured now, Wiki-OS allows incoming HTTP connections from any host, but outgoing connections are only permitted to the original host (and outgoing connections can only use the WebClient-- outgoing raw socket connections are not allowed).

This is interesting. If I'm reading that file correctly, it seems you could write a Wiki-OS network server but not a DDOS vehicle.

[1] "Security In Silverlight 2" http://msdn.microsoft.com/en-us/magazine/cc765416.aspx

[2] "Network Security Access Restrictions in Silverlight" http://msdn.microsoft.com/en-us/library/cc645032(VS.95).aspx

2 comments

With regards to the "infinite" program, I meant a DOS on YOUR machine, completely irrespective of network access. ...at least enough to force you to close the tab or the browser. I assume the sandbox is good enough to keep the process from causing the machine to become unresponsive, but hey...

Your conclusion is quite interesting, with respect to the possibilities of wiki-os. That's potentially a quite powerful feature.

In short, it's like Flash.