OpenBSD Pending ARP Request Remote DoS Vulnerability

OpenBSD is vulnerable to a remotely exploitable denial of service condition. The problem seems to be a lack of limits on the storage of pending arp requests, and a failure to handle the condition of too many. If an attacker somehow causes a victim machine to send out too many arp requests, it can cause a kernel panic and the target system to halt.

If an OpenBSD machine is on a network with a large address space (much more than a class C) an attacker can send it spoofed packets with addresses of hosts within its network. The victim host would then send out arp requests to find the MAC address for each host. If a sufficient number of arp requests are sent out, the kernel will panic with the message:

"out of space in kmem_map"

and freeze.


 

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