1. Many corporations use proxies so everyone appears to come from one IP address. A session based only on IP will have some pretty bad results like session jumping without people trying.
2. Large ISPs (AOL, Sympatico.ca, etc...) use super proxies that cause their clients to not only come from 1 IP but also these clients can hop across entire class A networks. This means your users get pretty mad when they keep getting kicked off.
3. Given 1 and 2 will cause you all sorts of problems it is easier (not more secure) to go with psuedo-random session-ids.
If you have an application that is in a tightly controlled environment (like LAN access only) then IPs can be considered. Although with remote access/VPN and B2B access this can also be problematic.
On Nov 17, 2003, at 1:16 PM, Thomas M. Duffey wrote:
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Hi All,
Sorry if this is common knowledge or regularly discussed; I'm fairly new to the list. I see quite a few messages on this and other security lists about session hijacking in Web applications. Isn't it good defense for a programmer to store the IP address of the client when the session is initiated, and then compare that address against the client for each subsequent request, destroying the session if the address changes? Do many programmers really overlook this simple method to protect against such an attack? It's not perfect but should significantly increase the difficulty of such an attack with little or no annoying side effects for the legitimate user. Would it be useful to extend the session modules of the common Web scripting languages (e.g. PHP) to enable an IP address check by default?
Best Regards,
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