Are HTTP cookies port specific?

Question

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.

Answer 1

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.

Answer 2

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:

1. 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.

Answer 3

This is a big gray area in cookie SOP (Same Origin Policy).

Theoretically, you can specify port number in the domain and the cookie will not be shared. In practice, this doesn't work with several browsers and you will run into other issues. So this is only feasible if your sites are not for general public and you can control what browsers to use.

The better approach is to get 2 domain names for the same IP and not relying on port numbers for cookies.

Answer 4

An alternative way to go around the problem, is to make the name of the session cookie be port related. For example:

• mysession8080 for the server running on port 8080
• mysession8000 for the server running on port 8000

Your code could access the webserver configuration to find out which port your server uses, and name the cookie accordingly.

Keep in mind that your application will receive both cookies, and you need to request the one that corresponds to your port.

There is no need to have the exact port number in the cookie name, but this is more convenient.

In general, the cookie name could encode any other parameter specific to the server instance you use, so it can be decoded by the right context.

Answer 5

It's optional.

The port may be specified so cookies can be port specific. It's not necessary, the web server / application must care of this.

Source: German Wikipedia article, RFC2109, Chapter 4.3.1

Answer 6

In IE 8, cookies (verified only against localhost) are shared between ports. In FF 10, they are not.

I've posted this answer so that readers will have at least one concrete option for testing each scenario.