Q:

Are HTTP cookies port specific?

I have two HTTP services running on one machine. I just want to know if they share their cookies or whether the browser distinguishes between the two server sockets.

A:

The current cookie specification is RFC 6265, which replaces RFC 2109 and RFC 2965 (both RFCs are now marked as "Historic") and formalizes the syntax for real-world usages of cookies.  It clearly states:

Introduction

...
For historical reasons, cookies contain a number of security and privacy infelicities.  For example, a server can indicate that a given cookie is intended for "secure" connections, but the Secure attribute does not provide integrity in the presence of an active network attacker.  Similarly, cookies for a given host are shared across all the ports on that host, even though the usual "same-origin policy" used by web browsers isolates content retrieved via different ports.

And also:

8.5.  Weak Confidentiality
Cookies do not provide isolation by port.  If a cookie is readable by a service running on one port, the cookie is also readable by a service running on another port of the same server.  If a cookie is writable by a service on one port, the cookie is also writable by a service running on another port of the same server.  For this reason, servers SHOULD NOT both run mutually distrusting services on different ports of the same host and use cookies to store security sensitive information.

A:

According to RFC2965 3.3.1 (which might or might not be followed by browsers), unless the port is explicitly specified via the port parameter of the Set-Cookie header, cookies might or might not be sent to any port.
Google's Browser Security Handbook says: by default, cookie scope is limited to all URLs on the current host name - and not bound to port or protocol information. and some lines later There is no way to limit cookies to a single DNS name only [...] likewise, there is no way to limit them to a specific port. (Also, keep in mind, that IE does not factor port numbers into its same-origin policy at all.)
So it does not seem to be safe to rely on any well-defined behavior here.

A:

This is a really old question but I thought I would add a workaround I used.
I have two services running on my laptop (one on port 3000 and the other on 4000).
When I would jump between (http://localhost:3000 and http://localhost:4000), Chrome would pass in the same cookie, each service would not understand the cookie and generate a new one.   
I found that if I accessed http://localhost:3000 and http://127.0.0.1:4000, the problem went away since Chrome kept a cookie for localhost and one for 127.0.0.1.
Again, noone may care at this point but it was easy and helpful to my situation.

