How to Bypass the IDS/IPS

The quality of an IDS or IPS signature may be what stands between you and a targeted attack, says researcher Simple Nomad, a.k.a. Mark Loveless, who will demonstrate gaping holes he's found in IDS and IPS products next week at IT Security World in San Francisco.

"A lot of people say the whole model of IDS/IPS is broken," says Loveless, who will present his latest research on bypassing IDS and IPS systems. "But the problem here boils down to poor signature-writing in some instances... Good signature-writing is effective."

One big problem is some signatures for filtering exploits are written to the publicly disclosed exploit, rather than the underlying vulnerability, he says. So if a known exploit's payload code is 4,096 bytes, for instance, the IDS or IPS signature would "look" for that characteristic to filter out the exploit. But a clever attacker could merely alter the size of the exploit's payload to, say, 5,000 bytes to avoid detection by the IDS or IPS.

"That happens a lot -- signature-writers write against the exploit as opposed to the vulnerability," Loveless says, and since most vendors outsource at least some, if not all, of their IDS/IPS signatures, this can provide attackers an easy way in.