Gauntlet Firewall Denial of Service Attack

Gauntlet Firewall Denial of Service Attack

There is a vulnerability in Gauntlet Firewall 5.0 which allows an attacker to remotely cause a denial of service. The vulnerability occurs because Gauntlet Firewall cannot handle a condition where an ICMP Protocol Problem packet's (ICMP_PARAMPROB) encapsulated IP packet has a random protocol field and certain IP options set. When this specially constructed packet ( [ICMP PARAMPROB][IP with random protocol code and some ip options] ) is sent THROUGH the Gauntlet Firewall (not to the firewall itself), the firewall will hang, looking for the packet in it's transparency tables.

The packet structure looks like this:

Begin Packet
------------------------------------------
[NORMAL IP HEADER]

[ICMP PARAMPROB HEADER]

-- encapsulated ip packet --

[IP HEADER]

(important fields in ip header)

ip_p = 98 (let's specify a protocol that doesn't exist)
ip_hl = 0xf (stuff options)

------------------------------------------
End Packet

An attacker would do the following:

Construct the [ip-icmp-ip] packet using a raw socket (SOCK_RAW) with the fields set accordingly, destination set to any machine behind the firewall.

Send the packet(s).

The number of packets that need to be sent depends on the platform (ie Sol on a Sparc vs BSDI).

The consequence of this vulnerability being exploited is the target Gauntlet 5.0 firewall being remotely locked up. It should be expected that an attacker would send packets with spoofed source addresses in the ip header making it difficult to trace.