The authentication technology used by Sitekey, Bank of America's online customer service system, is flawed and could make the bank vulnerable to denial-of-service attacks, a vendor said yesterday in a report that was disputed by both the bank and its primary contractor.

The two-factor authentication system offered by Bank of America, which allows a user to select a separate image file to help verify his/her identity, was developed by Passmark, an authentication tool vendor now owned by RSA Security.

But in a bit of vendor gamesmanship, the vulnerability report was issued by Sestus, a Passmark rival that also makes multi-factor authentication technology. Sestus, maker of PhishCops, has been critical of the Passmark technology in the past, publishing other documents that put Sitekey in a negative light.

In this case, however, Sestus reported the discovery of a "previously unreported vulnerability" in the Bank of America system that would enable an attacker to exploit the bank's lockout process to launch a denial-of-service attack on Sitekey, effectively preventing customers from accessing their accounts online.

"It appears that this lockout process can be exploited by malicious hackers to remotely lock out customers from their accounts en masse, or used by fraudsters in a hybrid lockout/phishing attack to access the actual account," the report said. The researchers did not publish a proof of concept with the vulnerability report.

In a series of three different scenarios, Sestus described how an attacker might use scripts and commonly-used login words to guess Bank of America customer login information, then type invalid information when the system requests the second authentication factor. Such an exploit would effectively lock users out of their accounts and tie up Bank of America systems, the vendor said. Attackers might also create a look-alike "error" page to phish personal information away from frustrated users, according to the report.

The vulnerability is not unique to Sitekey, but it could be exploited in any system that requests personal information before verifying the authenticity of the Web page, Sestus observed.

According to a Bank of America spokeswoman, the vulnerability doesn't threaten the safety of users' data. "It's not an issue that poses a risk to customers' information," she says. However, the vulnerability could lock out users if a hacker launched a denial-of-service attack, she says, and "anything that would be an inconvenience to our customers would be a concern for us."

Louie Gasparini, CTO of the RSA unit that now owns the Passmark technology, put a finer point on his response. "There's no vulnerability here that hasn't been in online banking systems for the past 10 years," he says. "This is the way the [banking authentication] system has always worked, and it's not unique to Sitekey or Passmark."

— Tim Wilson, Site Editor, Dark Reading