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Occasional visitors to my sites send one or more cookies that were never set by my hosts. Sometimes it's an obvious bot. Sometimes it's even an attempt to exploit. But occasionally it looks like a reasonably legit visit, except for the cookies which are mundane like the date or an IP address.

Are there legitimate reasons why a user agent would deliver cookies to a host which never set them? Do any of the popular human-powered browsers ever do this?

  • Its possible the user's browser has been hacked – Mike Feb 13 '18 at 16:07
  • Possible. Also possible it's a well-spoofed bot. But the cookies are innocuous, like date, so I wonder what the purpose is (whether legit or not). – pseudon Feb 13 '18 at 16:52
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...cookies that were never set by my hosts

Is it possible that a previous version of the site, or even the previous owner of the domain, set cookies with a very long (years+) expiry?

Are there legitimate reasons why a user agent would deliver cookies to a host which never set them?

No. It would make no sense. It just bloats the request with meaningless data (unless the site in question is expecting it).

Do any of the popular human-powered browsers ever do this?

I very much doubt it. I've never seen this behaviour with the big named browsers.

However, it may be possible for a rogue browser extension to send these cookies? See https://security.stackexchange.com/questions/15259/worst-case-scenario-what-can-a-chrome-extension-do-with-your-data-on-all-websi

Sometimes it's an obvious bot.

My bet would be that it's a non-obvious bot testing for exploits.

  • As far as I know, the domains affected had no prior owners, and I've never had these cookies on them. I'm going to apply my confirmation bias and mark this one Answered, but I still welcome any dissenting opinions. – pseudon Feb 14 '18 at 16:39

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