The File Transfer Protocol (FTP) has attracted renewed interest lately, but not in a good way: The bad guys are now using the ‘70s disco-era file transfer technology to serve up bot malware, and even as a backdoor into some enterprises that neglect to lock down their FTP servers.
Researchers at F-Secure have spotted a new wave of exploits that use FTP -- rather than a malicious URL, or the conspicuous email attachment -- to deliver their malware payloads. “As SMTP and HTTP are much better filtered for malware, FTP might be the best transport protocol for a virus writer,” says Mikko Hypponen, chief research officer for F-Secure. “We've just started to observe this phenomenon -- it's not widespread yet, but likely to increase.”
Last month, researchers at Finjan stumbled onto a cache of stolen FTP server administrative credentials that put nearly 9,000 FTP servers at some major global companies at risk, demonstrating just how widespread the old-school FTP remains at many organizations. Cybercriminals were selling a new crimeware package that would automatically infect those servers, some of which were from the world's top 100 domains. (See Stolen FTP Credentials Offered for Sale: Major Firms at Risk.)
F-Secure’s team last week discovered malicious Hallmark greeting card spam messages aimed at recruiting bots. The messages’ links to “view” the greeting instead take the victims to a bot-infected machine serving as an FTP site. The code it downloads is actually a variant of the Zapchast mIRC-bot, according to F-Secure. Instead of receiving the greeting, the user becomes a bot.
So why this retro-borne attack, especially when use of FTP is on the wane? FTP today is often a forgotten or unknown hole in the security of an organization -- not many enterprises bother to monitor it. And for bot herders, it’s just another means of moving malware.
“FTP is more popular than anyone knows -- a lot of people still send FTP stuff back and forth because it’s easy to do,” says Taher Elgamal, CTO of Tumbleweed Communications, which sells secure FTP software. And from the bad guy’s perspective, FTP is less likely to be blocked than an instant message, he says. “FTP is sort of left alone because it’s supposed to be an old thing no one cares about. But it’s an effective protocol for transferring large files... That’s why we’re seeing this [attack] phenomenon.”
Elgamal says the bad guys can hop on Port 80 and ship FTP through that port, for example, and a firewall wouldn’t block the file transfer. Some Internet gateways scan for FTP traffic, such as F-Secure’s Internet Gatekeeper, which does so by default. But many organizations just don’t bother scanning for FTP traffic at all either because they don’t consider it a risk or they don’t realize it’s being used, security experts say.
Still, the FTP-borne attack obviously won’t ever be as big as an HTTP-borne one. “Most companies wouldn't set up a new FTP site any more -- it's so old school. [But] the [FTP] sites that are out there are old and often forgotten about and poorly protected,” F-Secure’s Hypponen says.
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