Node: DOS: js expression make nodejs crash

[phra]

• Version: 6.9.1
• Platform: Linux kali 4.7.0-kali1-686-pae SMP Debian 4.7.6-1kali1 (2016-10-17) i686 GNU/Linux
• Subsystem: js built in prototypes

hi,

i was doing some javascript sorcery and i found out that the following js expression make the nodejs kill itself because it's tampering the prototype of Array.

Array.prototype.push = Array.prototype.push.bind(Array.prototype);

e.g.

> Array.prototype.push = Array.prototype.push.bind(Array.prototype)                                                  
[Function: bound push]                                       
> internal/process/next_tick.js:67            
      callback();                
      ^                                                

TypeError: callback is not a function  
    at _combinedTickCallback (internal/process/next_tick.js:67:7)
    at process._tickDomainCallback (internal/process/next_tick.js:122:9)

nodejs is crashing at this line -> https://github.com/nodejs/node/blob/master/lib/internal/process/next_tick.js#L67
i think that making not writable and not configurable the prototypes of built in types can prevent such very evil things.

what do you think about guys?

[cjihrig]

Node shouldn't mess with the built ins if possible. By you doing so, you shouldn't be surprised that things break. We might be able to work around it by storing a reference to the original function before user code can run, but I'm not sure if it's worth it.

[phra]

imho it's a security issue called denial of service.
i think that the best solution is a default setting that freeze the builtin prototypes, and if someone has to deal with them can just pass a flag to the node executable to disable the default setting and restore the original behaviour.

[cjihrig]

Freezing the builtins would probably break a ton of code. Also, how would an attacker execute such an attack? It seems like they would have to already be in a position to execute arbitrary code, in which case they could do much worse.

[mscdex]

I agree with @cjihrig. If an unauthorized person is able to modify your server code, then being worried about such a person adding that kind of breaking code is probably the least of your worries.

[phra]

that's for sure, obviously.

[phra]

just saw that the node exits without a SEGV so RCE is out of scope with this expression.
btw if there are changes to some prototype that can make v8/node crash with a SEGV, an open road to RCE with the user running the node instance is possible, so outside the v8 vm context. (beyond ASRL, etc)

for more infos: https://blog.scrt.ch/2013/03/24/mongodb-0-day-ssji-to-rce/