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

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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 test code try out this:

from pyvirtualdisplay import Display
from selenium import webdriver

display = Display(visible=1, size=(1600, 902))
display.start()
chrome_options = webdriver.ChromeOptions()
chrome_options.add_argument('--disable-extensions')
chrome_options.add_argument('--profile-directory=Default')
chrome_options.add_argument("--incognito")
chrome_options.add_argument("--disable-plugins-discovery");
chrome_options.add_argument("--start-maximized")
driver = webdriver.Chrome(chrome_options=chrome_options)
driver.delete_all_cookies()
driver.set_window_size(800,800)
driver.set_window_position(0,0)
print 'arguments done'
driver.get('http://stubhub.com')

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 stubhub.com 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:

{"appName":"Netscape","platform":"Linuxx86_64","cookies":1,"syslang":"en-US","userlang":"en-
US","cpu":"","productSub":"20030107","setTimeout":1,"setInterval":1,"plugins":
{"0":"ChromePDFViewer","1":"ShockwaveFlash","2":"WidevineContentDecryptionMo
dule","3":"NativeClient","4":"ChromePDFViewer"},"mimeTypes":
{"0":"application/pdf","1":"ShockwaveFlashapplication/x-shockwave-
flash","2":"FutureSplashPlayerapplication/futuresplash","3":"WidevineContent
DecryptionModuleapplication/x-ppapi-widevine-
cdm","4":"NativeClientExecutableapplication/x-
nacl","5":"PortableNativeClientExecutableapplication/x-
pnacl","6":"PortableDocumentFormatapplication/x-google-chrome-
pdf"},"screen":{"width":1600,"height":900,"colorDepth":24},"fonts":
{"0":"monospace","1":"DejaVuSerif","2":"Georgia","3":"DejaVuSans","4":"Trebu
chetMS","5":"Verdana","6":"AndaleMono","7":"DejaVuSansMono","8":"LiberationM
ono","9":"NimbusMonoL","10":"CourierNew","11":"Courier"}}

It’s identical in Selenium and in Chrome.

VPNs work for a single use, but they get detected after I load the first page. Clearly some JavaScript is being run to detect Selenium.

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Replacing cdc_ string

You can use vim or perl to replace the cdc_ string in chromedriver. See answer by @Erti-Chris Eelmaa to learn more about that string and how it’s a detection point.

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.

Our goal is to alter the cdc_ string, which looks something like $cdc_lasutopfhvcZLmcfl.

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. Replace all instances of cdc_ with dog_ by typing :%s/cdc_/dog_/g.
    • dog_ is just an example. You can choose anything as long as it has the same amount of characters as the search string (e.g., cdc_), otherwise the chromedriver will fail.
  2. To save the changes and quit, type :wq! and press return.
    • If you need to quit without saving changes, type :q! and press return.

Using Perl

The line below replaces all cdc_ occurrences with dog_. Credit to Vic Seedoubleyew:

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

Make sure that the replacement string (e.g., dog_) has the same number of characters as the search string (e.g., cdc_), otherwise the chromedriver will fail.

Wrapping Up

To verify that all occurrences of cdc_ were replaced:

grep "cdc_" /path/to/chromedriver

If no output was returned, the replacement was successful.

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’ve successfully altered the driver.

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, etc.

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