Can a website detect when you are using selenium with chromedriver?

Can a website detect when you are using selenium with chromedriver?

I’ve been testing out Selenium with Chromedriver and I noticed that some pages can detect that you’re using Selenium even though there’s no automation at all. Even when I’m just browsing manually just using chrome through Selenium and Xephyr I often get a page saying that suspicious activity was detected. I’ve checked my user agent, and my browser fingerprint, and they are all exactly identical to the normal chrome browser.
When I browse to these sites in normal chrome everything works fine, but the moment I use Selenium I’m detected.
In theory chromedriver and chrome should look literally exactly the same to any webserver, but somehow they can detect it.
If you want some testcode try out this:
from pyvirtualdisplay import Display
from selenium import webdriver

display = Display(visible=1, size=(1600, 902))
chrome_options = webdriver.ChromeOptions()
driver = webdriver.Chrome(chrome_options=chrome_options)
print ‘arguments done’

If you browse around stubhub you’ll get redirected and ‘blocked’ within one or two requests. I’ve been investigating this and I can’t figure out how they can tell that a user is using Selenium.
How do they do it?
I installed the Selenium IDE plugin in Firefox and I got banned when I went to in the normal firefox browser with only the additional plugin.
When I use Fiddler to view the HTTP requests being sent back and forth I’ve noticed that the ‘fake browser\’s’ requests often have ‘no-cache’ in the response header.
results like this Is there a way to detect that I’m in a Selenium Webdriver page from Javascript suggest that there should be no way to detect when you are using a webdriver. But this evidence suggests otherwise.
The site uploads a fingerprint to their servers, but I checked and the fingerprint of selenium is identical to the fingerprint when using chrome.
This is one of the fingerprint payloads that they send to their servers

Its identical in selenium and in chrome
VPNs work for a single use but get detected after I load the first page. Clearly some javascript is being run to detect Selenium.


Solution 1:

For Mac Users

Replacing cdc_ variable using Vim or Perl

You can use vim, or as @Vic Seedoubleyew has pointed out in the answer by @Erti-Chris Eelmaa, perl, to replace the cdc_ variable in chromedriver(See post by @Erti-Chris Eelmaa to learn more about that variable). Using vim or perl prevents you from having to recompile source code or use a hex-editor. Make sure to make a copy of the original chromedriver before attempting to edit it. Also, the methods below were tested on chromedriver version 2.41.578706.

Using Vim

vim /path/to/chromedriver

After running the line above, you’ll probably see a bunch of gibberish. Do the following:

  1. Search for cdc_ by typing /cdc_ and pressing return.
  2. Enable editing by pressing a.
  3. Delete any amount of $cdc_lasutopfhvcZLmcfl and replace what was deleted with an equal amount characters. If you don’t, chromedriver will fail.
  4. After you’re done editing, press esc.
  5. To save the changes and quit, type :wq! and press return.
  6. If you don’t want to save the changes, but you want to quit, type :q! and press return.
  7. You’re done.
Related:  .setAttribute(“disabled”, false); changes editable attribute to false

Go to the altered chromedriver and double click on it. A terminal window should open up. If you don’t see killed in the output, you successfully altered the driver.

Using Perl

The line below replaces cdc_ with dog_:

perl -pi -e 's/cdc_/dog_/g' /path/to/chromedriver

Make sure that the replacement string has the same number of characters as the search string, otherwise the chromedriver will fail.

Perl Explanation

s///g denotes that you want to search for a string and replace it globally with another string (replaces all occurrences).

e.g., s/string/replacment/g


s/// denotes searching for and replacing a string.

cdc_ is the search string.

dog_ is the replacement string.

g is the global key, which replaces every occurrence of the string.

How to check if the Perl replacement worked

The following line will print every occurrence of the search string cdc_:

perl -ne 'while(/cdc_/g){print "$&\n";}' /path/to/chromedriver

If this returns nothing, then cdc_ has been replaced.

Conversely, you can use the this:

perl -ne 'while(/dog_/g){print "$&\n";}' /path/to/chromedriver

to see if your replacement string, dog_, is now in the chromedriver binary. If it is, the replacement string will be printed to the console.

Go to the altered chromedriver and double click on it. A terminal window should open up. If you don’t see killed in the output, you successfully altered the driver.

Wrapping Up

After altering the chromedriver binary, make sure that the name of the altered chromedriver binary is chromedriver, and that the original binary is either moved from its original location or renamed.

My Experience With This Method

I was previously being detected on a website while trying to log in, but after replacing cdc_ with an equal sized string, I was able to log in. Like others have said though, if you’ve already been detected, you might get blocked for a plethora of other reasons even after using this method. So you may have to try accessing the site that was detecting you using a VPN, different network, or what have you.

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Solution 2:

Basically the way the selenium detection works, is that they test for pre-defined javascript variables which appear when running with selenium. The bot detection scripts usually look anything containing word “selenium” / “webdriver” in any of the variables (on window object), and also document variables called $cdc_ and $wdc_. Of course, all of this depends on which browser you are on. All the different browsers expose different things.

For me, I used chrome, so, all that I had to do was to ensure that $cdc_ didn’t exist anymore as document variable, and voila (download chromedriver source code, modify chromedriver and re-compile $cdc_ under different name.)

this is the function I modified in chromedriver:


function getPageCache(opt_doc) {
  var doc = opt_doc || document;
  //var key = '$cdc_asdjflasutopfhvcZLmcfl_';
  var key = 'randomblabla_';
  if (!(key in doc))
    doc[key] = new Cache();
  return doc[key];

(note the comment, all I did I turned $cdc_ to randomblabla_.

Here is a pseudo-code which demonstrates some of the techniques that bot networks might use:

runBotDetection = function () {
    var documentDetectionKeys = [

    var windowDetectionKeys = [

    for (const windowDetectionKey in windowDetectionKeys) {
        const windowDetectionKeyValue = windowDetectionKeys[windowDetectionKey];
        if (window[windowDetectionKeyValue]) {
            return true;
    for (const documentDetectionKey in documentDetectionKeys) {
        const documentDetectionKeyValue = documentDetectionKeys[documentDetectionKey];
        if (window['document'][documentDetectionKeyValue]) {
            return true;

    for (const documentKey in window['document']) {
        if (documentKey.match(/\$[a-z]dc_/) && window['document'][documentKey]['cache_']) {
            return true;

    if (window['external'] && window['external'].toString() && (window['external'].toString()['indexOf']('Sequentum') != -1)) return true;

    if (window['document']['documentElement']['getAttribute']('selenium')) return true;
    if (window['document']['documentElement']['getAttribute']('webdriver')) return true;
    if (window['document']['documentElement']['getAttribute']('driver')) return true;

    return false;

according to user @szx, it is also possible to simply open chromedriver.exe in hex editor, and just do the replacement manually, without actually doing any compiling.

Solution 3:

As we’ve already figured out in the question and the posted answers, there is an anti Web-scraping and a Bot detection service called “Distil Networks” in play here. And, according to the company CEO’s interview:

Even though they can create new bots, we figured out a way to identify
Selenium the a tool they’re using, so we’re blocking Selenium no
matter how many times they iterate on that bot
. We’re doing that now
with Python and a lot of different technologies. Once we see a pattern
emerge from one type of bot, then we work to reverse engineer the
technology they use and identify it as malicious.

It’ll take time and additional challenges to understand how exactly they are detecting Selenium, but what can we say for sure at the moment:

  • it’s not related to the actions you take with selenium – once you navigate to the site, you get immediately detected and banned. I’ve tried to add artificial random delays between actions, take a pause after the page is loaded – nothing helped
  • it’s not about browser fingerprint either – tried it in multiple browsers with clean profiles and not, incognito modes – nothing helped
  • since, according to the hint in the interview, this was “reverse engineering”, I suspect this is done with some JS code being executed in the browser revealing that this is a browser automated via selenium webdriver
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Decided to post it as an answer, since clearly:

Can a website detect when you are using selenium with chromedriver?


Also, what I haven’t experimented with is older selenium and older browser versions – in theory, there could be something implemented/added to selenium at a certain point that Distil Networks bot detector currently relies on. Then, if this is the case, we might detect (yeah, let’s detect the detector) at what point/version a relevant change was made, look into changelog and changesets and, may be, this could give us more information on where to look and what is it they use to detect a webdriver-powered browser. It’s just a theory that needs to be tested.

Solution 4:

Example of how it’s implemented on

try {
 if (window.document.documentElement.getAttribute("webdriver")) return !+[]
} catch (IDLMrxxel) {}
try {
 if ("_Selenium_IDE_Recorder" in window) return !+""
} catch (KknKsUayS) {}
try {
 if ("__webdriver_script_fn" in document) return !+""

Solution 5:

partial interface Navigator {
readonly attribute boolean webdriver;

The webdriver IDL attribute of the Navigator interface must return the value of the webdriver-active flag, which is initially false.

This property allows websites to determine that the user agent is under control by WebDriver, and can be used to help mitigate denial-of-service attacks.

Taken directly from the 2017 W3C Editor’s Draft of WebDriver. This heavily implies that at the very least, future iterations of selenium’s drivers will be identifiable to prevent misuse. Ultimately, it’s hard to tell without the source code, what exactly causes chrome driver in specific to be detectable.

Solution 6:

Try to use selenium with a specific user profile of chrome, That way you can use it as specific user and define any thing you want, When doing so it will run as a ‘real’ user, look at chrome process with some process explorer and you’ll see the difference with the tags.

For example:

username = os.getenv("USERNAME")
userProfile = "C:\\Users\\" + username + "\\AppData\\Local\\Google\\Chrome\\User Data\\Default"
options = webdriver.ChromeOptions()
# add here any tag you want.
options.add_experimental_option("excludeSwitches", ["ignore-certificate-errors", "safebrowsing-disable-download-protection", "safebrowsing-disable-auto-update", "disable-client-side-phishing-detection"])
chromedriver = "C:\Python27\chromedriver\chromedriver.exe"
os.environ[""] = chromedriver
browser = webdriver.Chrome(executable_path=chromedriver, chrome_options=options)

chrome tag list here