Just days after details of a critical bug in the Domain Name System (DNS) software went public, researchers released attack code that can silently redirect users to unintended sites.

HD Moore, the creator of the Metasploit penetration testing framework, and a hacker who goes by the alias "I)ruid," published the attack code in two parts Wednesday and Thursday to several security mailing lists and to the Computer Academic Underground Web site.

The two exploits do essentially the same thing, said Andrew Storms, director of security operations at nCircle Network Security; both poison a DNS server's cache, and therefore can, at least temporarily, replace the legitimate addresses in that cache with bogus destinations. Users steering to what they believe are valid sites could, if they pull the routing information from a victimized DNS server, be sent instead to a fake site such as a phony banking site, where they could be easily duped into divulging confidential information.

Wednesday's exploit, explained Storms, lets an attacker poison a DNS server's cache with a single malicious entry, but Thursday's attack code allows a hacker to poison large quantities of domains with one fell swoop. "This second exploit has the potential for a much larger impact," said Storms, "and could result in potentially thousands of fake addresses inserted into a DNS server's cache.

HD Moore, however, noted that the single entry exploit of Tuesday gives attackers more anonymity, while Thursday's exploit requires hackers to have a real DNS server. "That means they'll be less anonymous," Moore said, adding that it would be possible to trace the DNS requests back to the fake server operated by the attacker, then have it taken offline by, for instance, the host provider.

"Both [kinds of attacks] will be difficult to detect," Storm said. "It will probably take an end user to raise the flag when they go to their banking site, for example, and then report, 'Hey, this just doesn't look quite right.'" Digging through the enormous amount of data generated by a DNS server -- hundreds of thousands of results in an hour at a company like nCircle, said Storms -- is simply impossible.

The DNS cache poisoning bug exploited by Moore's and I)ruid's attack code was first announced earlier this month by Dan Kaminsky, director of penetration testing at US-based IOActive. The bug, which Kaminsky uncovered earlier this year, was patched that same day by several major vendors, including Cisco Systems, Internet Systems Consortium and Microsoft.

Although Kaminsky declined to publicly disclose technical information, he briefed several fellow security researchers after he was criticized for overstating the seriousness of the threat. Those researchers recanted, and said Kaminsky's research was on target.

Monday, however, a German hacker went public with his guesses about the bug's details. His speculation was confirmed later in the day by Matasano Security, a consultancy that included at least one researcher who had been briefed on the bug by Kaminsky.