How does Facebook disable the browser's integrated Developer Tools?

I'm a security engineer at Facebook and this is my fault. We're testing this for some users to see if it can slow down some attacks where users are tricked into pasting (malicious) JavaScript code into the browser console.

Just to be clear: trying to block hackers client-side is a bad idea in general; this is to protect against a specific social engineering attack.

If you ended up in the test group and are annoyed by this, sorry. I tried to make the old opt-out page (now help page) as simple as possible while still being scary enough to stop at least some of the victims.

The actual code is pretty similar to @joeldixon66's link; ours is a little more complicated for no good reason.

Chrome wraps all console code in

with ((console && console._commandLineAPI) || {}) {
  <code goes here>
}

... so the site redefines console._commandLineAPI to throw:

Object.defineProperty(console, '_commandLineAPI',
   { get : function() { throw 'Nooo!' } })

This is not quite enough (try it!), but that's the main trick.

Epilogue: The Chrome team decided that defeating the console from user-side JS was a bug and fixed the issue, rendering this technique invalid. Afterwards, additional protection was added to protect users from self-xss.

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I located the Facebook's console buster script using Chrome developer tools. Here is the script with minor changes for readability. I have removed the bits that I could not understand:

Object.defineProperty(window, "console", {
    value: console,
    writable: false,
    configurable: false
});

var i = 0;
function showWarningAndThrow() {
    if (!i) {
        setTimeout(function () {
            console.log("%cWarning message", "font: 2em sans-serif; color: yellow; background-color: red;");
        }, 1);
        i = 1;
    }
    throw "Console is disabled";
}

var l, n = {
        set: function (o) {
            l = o;
        },
        get: function () {
            showWarningAndThrow();
            return l;
        }
    };
Object.defineProperty(console, "_commandLineAPI", n);
Object.defineProperty(console, "__commandLineAPI", n);

With this, the console auto-complete fails silently while statements typed in console will fail to execute (the exception will be logged).

References:

Object.defineProperty

Object.getOwnPropertyDescriptor

Chrome's console.log function (for tips on formatting output)

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I couldn't get it to trigger that on any page. A more robust version of this would do it:

window.console.log = function(){
    console.error('The developer console is temp...');
    window.console.log = function() {
        return false;
    }
}

console.log('test');

To style the output: Colors in JavaScript console

Edit Thinking @joeldixon66 has the right idea: Disable JavaScript execution from console « ::: KSpace :::

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Besides redefining console._commandLineAPI, there are some other ways to break into InjectedScriptHost on WebKit browsers, to prevent or alter the evaluation of expressions entered into the developer's console.

Edit:

Chrome has fixed this in a past release. - which must have been before February 2015, as I created the gist at that time

So here's another possibility. This time we hook in, a level above, directly into InjectedScript rather than InjectedScriptHost as opposed to the prior version.

Which is kind of nice, as you can directly monkey patch InjectedScript._evaluateAndWrap instead of having to rely on InjectedScriptHost.evaluate as that gives you more fine-grained control over what should happen.

Another pretty interesting thing is, that we can intercept the internal result when an expression is evaluated and return that to the user instead of the normal behavior.

Here is the code, that does exactly that, return the internal result when a user evaluates something in the console.

var is;
Object.defineProperty(Object.prototype,"_lastResult",{
   get:function(){
       return this._lR;
   },
   set:function(v){
       if (typeof this._commandLineAPIImpl=="object") is=this;
       this._lR=v;
   }
});
setTimeout(function(){
   var ev=is._evaluateAndWrap;
   is._evaluateAndWrap=function(){
       var res=ev.apply(is,arguments);
       console.log();
       if (arguments[2]==="completion") {
           //This is the path you end up when a user types in the console and autocompletion get's evaluated

           //Chrome expects a wrapped result to be returned from evaluateAndWrap.
           //You can use `ev` to generate an object yourself.
           //In case of the autocompletion chrome exptects an wrapped object with the properties that can be autocompleted. e.g.;
           //{iGetAutoCompleted: true}
           //You would then go and return that object wrapped, like
           //return ev.call (is, '', '({test:true})', 'completion', true, false, true);
           //Would make `test` pop up for every autocompletion.
           //Note that syntax as well as every Object.prototype property get's added to that list later,
           //so you won't be able to exclude things like `while` from the autocompletion list,
           //unless you wou'd find a way to rewrite the getCompletions function.
           //
           return res; //Return the autocompletion result. If you want to break that, return nothing or an empty object
       } else {
           //This is the path where you end up when a user actually presses enter to evaluate an expression.
           //In order to return anything as normal evaluation output, you have to return a wrapped object.

           //In this case, we want to return the generated remote object. 
           //Since this is already a wrapped object it would be converted if we directly return it. Hence,
           //`return result` would actually replicate the very normal behaviour as the result is converted.
           //to output what's actually in the remote object, we have to stringify it and `evaluateAndWrap` that object again.`
           //This is quite interesting;
           return ev.call (is, null, '(' + JSON.stringify (res) + ')', "console", true, false, true)
       }
   };
},0);

It's a bit verbose, but I thought I put some comments into it

So normally, if a user, for example, evaluates [1,2,3,4] you'd expect the following output:

https://i.stack.imgur.com/FLAnR.png

After monkeypatching InjectedScript._evaluateAndWrap evaluating the very same expression, gives the following output:

https://i.stack.imgur.com/1fOfj.png

As you see the little-left arrow, indicating output, is still there, but this time we get an object. Where the result of the expression, the array [1,2,3,4] is represented as an object with all its properties described.

I recommend trying to evaluate this and that expression, including those that generate errors. It's quite interesting.

Additionally, take a look at the is - InjectedScriptHost - object. It provides some methods to play with and get a bit of insight into the internals of the inspector.

Of course, you could intercept all that information and still return the original result to the user.

Just replace the return statement in the else path by a console.log (res) following a return res. Then you'd end up with the following.

https://i.stack.imgur.com/4X4Ep.png

End of Edit

This is the prior version which was fixed by Google. Hence not a possible way anymore.

One of it is hooking into Function.prototype.call

Chrome evaluates the entered expression by calling its eval function with InjectedScriptHost as thisArg

var result = evalFunction.call(object, expression);

Given this, you can listen for the thisArg of call being evaluate and get a reference to the first argument (InjectedScriptHost)

if (window.URL) {
    var ish, _call = Function.prototype.call;
    Function.prototype.call = function () { //Could be wrapped in a setter for _commandLineAPI, to redefine only when the user started typing.
        if (arguments.length > 0 && this.name === "evaluate" && arguments [0].constructor.name === "InjectedScriptHost") { //If thisArg is the evaluate function and the arg0 is the ISH
            ish = arguments[0];
            ish.evaluate = function (e) { //Redefine the evaluation behaviour
                throw new Error ('Rejected evaluation of: \n\'' + e.split ('\n').slice(1,-1).join ("\n") + '\'');
            };
            Function.prototype.call = _call; //Reset the Function.prototype.call
            return _call.apply(this, arguments);  
        }
    };
}

You could e.g. throw an error, that the evaluation was rejected.

https://i.imgur.com/YYDovbt.png

_{Here is an example where the entered expression gets passed to a CoffeeScript compiler before passing it to the evaluate function.}

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Netflix also implements this feature

(function() {
    try {
        var $_console$$ = console;
        Object.defineProperty(window, "console", {
            get: function() {
                if ($_console$$._commandLineAPI)
                    throw "Sorry, for security reasons, the script console is deactivated on netflix.com";
                return $_console$$
            },
            set: function($val$$) {
                $_console$$ = $val$$
            }
        })
    } catch ($ignore$$) {
    }
})();

They just override console._commandLineAPI to throw security error.

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This is actually possible since Facebook was able to do it. Well, not the actual web developer tools but the execution of Javascript in console.

See this: How does Facebook disable the browser's integrated Developer Tools?

This really wont do much though since there are other ways to bypass this type of client-side security.

When you say it is client-side, it happens outside the control of the server, so there is not much you can do about it. If you are asking why Facebook still does this, this is not really for security but to protect normal users that do not know javascript from running code (that they don't know how to read) into the console. This is common for sites that promise auto-liker service or other Facebook functionality bots after you do what they ask you to do, where in most cases, they give you a snip of javascript to run in console.

If you don't have as much users as Facebook, then I don't think there's any need to do what Facebook is doing.

Even if you disable Javascript in console, running javascript via address bar is still possible.

https://i.stack.imgur.com/pCtTk.png

https://i.stack.imgur.com/QxDLs.png

and if the browser disables javascript at address bar, (When you paste code to the address bar in Google Chrome, it deletes the phrase 'javascript:') pasting javascript into one of the links via inspect element is still possible.

Inspect the anchor:

https://i.stack.imgur.com/VHXyy.png

Paste code in href:

https://i.stack.imgur.com/hwmKo.png

https://i.stack.imgur.com/UTUFH.png

https://i.stack.imgur.com/kwLjP.png

Bottom line is server-side validation and security should be first, then do client-side after.

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Chrome changed a lot since the times facebook could disable console...

As per March 2017 this doesn't work anymore.

Best you can do is disable some of the console functions, example:

if(!window.console) window.console = {};
var methods = ["log", "debug", "warn", "info", "dir", "dirxml", "trace", "profile"];
for(var i=0;i<methods.length;i++){
    console[methods[i]] = function(){};
}

---

My simple way, but it can help for further variations on this subject. List all methods and alter them to useless.

  Object.getOwnPropertyNames(console).filter(function(property) {
     return typeof console[property] == 'function';
  }).forEach(function (verb) {
     console[verb] =function(){return 'Sorry, for security reasons...';};
  });

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Internally devtools injects an IIFE named getCompletions into the page, called when a key is pressed inside the Devtools console.

Looking at the source of that function, it uses a few global functions which can be overwritten.

By using the Error constructor it's possible to get the call stack, which will include getCompletions when called by Devtools.

Example:

const disableDevtools = callback => { const original = Object.getPrototypeOf; Object.getPrototypeOf = (...args) => { if (Error().stack.includes("getCompletions")) callback(); return original(...args); }; }; disableDevtools(() => { console.error("devtools has been disabled"); while (1); });

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an simple solution!

setInterval(()=>console.clear(),1500);

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I would go along the way of:

Object.defineProperty(window, 'console', {
  get: function() {

  },
  set: function() {

  }
});

---

I have a simple way here: window.console = function () {}

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In Firefox it dosen't do that, since Firefox is a developer browser, I think since the command WEBGL_debug_renderer_info is deprecated in Firefox and will be removed. Please use RENDERER and the error Referrer Policy: Less restricted policies, including ‘no-referrer-when-downgrade’, ‘origin-when-cross-origin’ and ‘unsafe-url’, will be ignored soon for the cross-site request: https://static.xx.fbcdn.net/rsrc.php/v3/yS/r/XDDAHSZfaR6.js?_nc_x=Ij3Wp8lg5Kz.

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This is not a security measure for weak code to be left unattended. Always get a permanent solution to weak code and secure your websites properly before implementing this strategy

The best tool by far according to my knowledge would be to add multiple javascript files that simply changes the integrity of the page back to normal by refreshing or replacing content. Disabling this developer tool would not be the greatest idea since bypassing is always in question since the code is part of the browser and not a server rendering, thus it could be cracked.

Should you have js file one checking for <element> changes on important elements and js file two and js file three checking that this file exists per period you will have full integrity restore on the page within the period.

Lets take an example of the 4 files and show you what I mean.

index.html

   <!DOCTYPE html>
   <html>
   <head id="mainhead">
   <script src="ks.js" id="ksjs"></script>
   <script src="mainfile.js" id="mainjs"></script>
   <link rel="stylesheet" href="style.css" id="style">
   <meta id="meta1" name="description" content="Proper mitigation against script kiddies via Javascript" >
   </head>
   <body>
   <h1 id="heading" name="dontdel" value="2">Delete this from console and it will refresh. If you change the name attribute in this it will also refresh. This is mitigating an attack on attribute change via console to exploit vulnerabilities. You can even try and change the value attribute from 2 to anything you like. If This script says it is 2 it should be 2 or it will refresh. </h1>
   <h3>Deleting this wont refresh the page due to it having no integrity check on it</h3>

   <p>You can also add this type of error checking on meta tags and add one script out of the head tag to check for changes in the head tag. You can add many js files to ensure an attacker cannot delete all in the second it takes to refresh. Be creative and make this your own as your website needs it. 
   </p>

   <p>This is not the end of it since we can still enter any tag to load anything from everywhere (Dependent on headers etc) but we want to prevent the important ones like an override in meta tags that load headers. The console is designed to edit html but that could add potential html that is dangerous. You should not be able to enter any meta tags into this document unless it is as specified by the ks.js file as permissable. <br>This is not only possible with meta tags but you can do this for important tags like input and script. This is not a replacement for headers!!! Add your headers aswell and protect them with this method.</p>
   </body>
   <script src="ps.js" id="psjs"></script>
   </html>

mainfile.js

   setInterval(function() {
   // check for existence of other scripts. This part will go in all other files to check for this file aswell. 
   var ksExists = document.getElementById("ksjs"); 
   if(ksExists) {
   }else{ location.reload();};

   var psExists = document.getElementById("psjs");
   if(psExists) {
   }else{ location.reload();};

   var styleExists = document.getElementById("style");
   if(styleExists) {
   }else{ location.reload();};


   }, 1 * 1000); // 1 * 1000 milsec

ps.js

   /*This script checks if mainjs exists as an element. If main js is not existent as an id in the html file reload!You can add this to all js files to ensure that your page integrity is perfect every second. If the page integrity is bad it reloads the page automatically and the process is restarted. This will blind an attacker as he has one second to disable every javascript file in your system which is impossible.

   */

   setInterval(function() {
   // check for existence of other scripts. This part will go in all other files to check for this file aswell. 
   var mainExists = document.getElementById("mainjs"); 
   if(mainExists) {
   }else{ location.reload();};

   //check that heading with id exists and name tag is dontdel.
   var headingExists = document.getElementById("heading"); 
   if(headingExists) {
   }else{ location.reload();};
   var integrityHeading = headingExists.getAttribute('name');
   if(integrityHeading == 'dontdel') {
   }else{ location.reload();};
   var integrity2Heading = headingExists.getAttribute('value');
   if(integrity2Heading == '2') {
   }else{ location.reload();};
   //check that all meta tags stay there
   var meta1Exists = document.getElementById("meta1"); 
   if(meta1Exists) {
   }else{ location.reload();};

   var headExists = document.getElementById("mainhead"); 
   if(headExists) {
   }else{ location.reload();};

   }, 1 * 1000); // 1 * 1000 milsec

ks.js

   /*This script checks if mainjs exists as an element. If main js is not existent as an id in the html file reload! You can add this to all js files to ensure that your page integrity is perfect every second. If the page integrity is bad it reloads the page automatically and the process is restarted. This will blind an attacker as he has one second to disable every javascript file in your system which is impossible.

   */

   setInterval(function() {
   // check for existence of other scripts. This part will go in all other files to check for this file aswell. 
   var mainExists = document.getElementById("mainjs"); 
   if(mainExists) {
   }else{ location.reload();};
   //Check meta tag 1 for content changes. meta1 will always be 0. This you do for each meta on the page to ensure content credibility. No one will change a meta and get away with it. Addition of a meta in spot 10, say a meta after the id="meta10" should also be covered as below.
   var x = document.getElementsByTagName("meta")[0];
   var p = x.getAttribute("name");
   var s = x.getAttribute("content");
   if (p != 'description') {
   location.reload();
   }
   if ( s != 'Proper mitigation against script kiddies via Javascript') {
   location.reload();
   }
   // This will prevent a meta tag after this meta tag @ id="meta1". This prevents new meta tags from being added to your pages. This can be used for scripts or any tag you feel is needed to do integrity check on like inputs and scripts. (Yet again. It is not a replacement for headers to be added. Add your headers aswell!)
   var lastMeta = document.getElementsByTagName("meta")[1];
   if (lastMeta) {
   location.reload();
   }
   }, 1 * 1000); // 1 * 1000 milsec

style.css

Now this is just to show it works on all files and tags aswell

   #heading {
   background-color:red;
   }

If you put all these files together and build the example you will see the function of this measure. This will prevent some unforseen injections should you implement it correctly on all important elements in your index file especially when working with PHP.

Why I chose reload instead of change back to normal value per attribute is the fact that some attackers could have another part of the website already configured and ready and it lessens code amount. The reload will remove all the attacker's hard work and he will probably go play somewhere easier.

Another note: This could become a lot of code so keep it clean and make sure to add definitions to where they belong to make edits easy in future. Also set the seconds to your preferred amount as 1 second intervals on large pages could have drastic effects on older computers your visitors might be using

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