The denial of service vulnerability enables hackers to crash IPSec VPN machines using a specially designed UDP packet. NTA Monitor said it would withhold details of the vulnerability because it is so dangerous.
Roy Hills, technical director of NTA Monitor said: "We believe this is a serious vulnerability. It's possible to identify Nortel VPN routers using UDP backoff fingerprinting and an attacker only needs to send a single, small UDP packet to identify the remote systems. We have determined that it's possible for an attacker with modest resources to scan the entire routed Internet address space within a few weeks and thus find all of the Nortel VPN router systems."
Hills said the attack was serious because it is possible to find Nortel devices on the Internet using simple hacker "fingerprinting" techniques. The attack also requires only a small piece of code to bring down thousands of machines at the same time: "This packet is less than 300 bytes in size, so an attacker with a 64Kb line could keep more than 7,000 Nortel VPN systems offline continuously, and someone with a 2Mb line has the potential to keep almost a quarter of a million systems offline."
NTA is urging companies to install a software patch that was issued by Nortel on Friday.
Nortel was not available for comment.
In March, NTA found a password flaw in Nortel's Contivity VPN client for Microsoft Windows.
Silicon.com's Dan Ilett reported from London. For more coverage from Silicon.com, click here.
Let me guess a Linux black box at fault