[VPN] Is IP address spoofing possible with ESP transport mode?

[Siddhartha Jain]

The need for origin authenticity is to avoid
man-in-the-middle attacks where an attacker sits in
the middle of the conversation and *proxies* the
connection. 

With ESP in trasnport mode, that isn't possible
because the payload is encrypted so a
man-in-the-middle wouldn't be able to grab the data.

Spoofing IP addresses with Transport-mode ESP will
only give you routing headaches ;)

- Siddhartha (CISSP)


 --- Son Phan <son_ml at freemail.hu> wrote: 
> Hello IPSec folks,
> 
> As far as I know IP header is not protected in ESP
> mode, so in transport 
> mode the source IP may be modified.
> 
> Imagine the following scenario:
> 
> -Bad guy Bob setup an transport ESP SA with server
> S. The SA is 
> identified by S's IP address, SPI and SA mode (ESP)
> 
> -After setting up this SA, Bob send an IP packet
> protected with this SA's 
> parameter, but put Victim Alice's IP address as into
> source IP address. 
> As {dest_IPaddr, SPI, mode} trio point to the valid
> SA, the packet can 
> be decrypted successfully. However the result will
> be a IP with fake 
> source IP address.
> 
> Question:
> -Can that case really happen or did I miss
> something?
> 
> -There is a source address field in SA. Is it
> mandatory to check this value 
> against the source IP address to protect the above
> case? I have some 
> doubt about it as it can be wildcast in many cases.
> 
> -Is there any measure to protect the case described
> here?



	
	
		
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