Black Hat: PKI Hack Demonstrates Flaws in Digital Certificate Technology

BLACK HAT USA -- LAS VEGAS -- The spotlight here this week was on another potentially broken piece of the Internet infrastructure as renowned white-hat hacker Dan Kaminsky today revealed critical bugs in the X.509 authentication scheme.

Kaminsky, who rocked the security community last year with his major DNS flaw find, said the potential for an X.509 meltdown and major hack is high, but not likely possible for at least another six months. "You can wait for it to blow up, or do something about it," says Kaminsky, director of penetration testing for IOActive. "This time, I don't want to see anything get 'owned.'"

Ironically, Kaminsky himself today was recovering from a targeted attack on his Website, email and Twitter accounts by a group of black hat hackers who stole passwords, emails, instant message chats from Kaminsky and former hacker Kevin Mitnick, and posted the information online. Kaminsky dismissed the attack "as nothing technically interesting" and likely began with a Web-borne exploit, he says.

Around 60 percent of attacks are due to weak or default passwords. "X.509 was supposed to be the solution" in authentication, Kaminsky says. "Businesses have spent hundreds of millions of dollars of investment in it. But there are things wrong structurally and technically with X.509." X.509 doesn't scale well, he says, and it can't delegate authority to issue certificates, for instance.

He noted that one of VeriSign's core root servers until recently used the older and weaker MD2 hash algorithm to sign certificates. "If a certificate is signed with MD2, it can accept everything," he says.

VeriSign no longer uses MD2 to sign any of its digital certificates, says Tim Callan, vice president of product marketing at VeriSign. "Last year, VeriSign implemented a process for transitioning off MD2 and, as of May 17th, the transition to the SHA-1 algorithm has been completed," he says.

Even so, browsers today still come with legacy [MD2] root certificates, Kaminsky says. "VeriSign's fix is to give new browsers something to ship. Microsoft, et al, are about making the old browsers ignore MD2 even if it is there. Both paths are helpful," he says.

Meanwhile, Kaminsky pointed to the work of another researcher who presented at Black Hat, Moxie Marlinspike, who demonstrated an attack that spoofs SSL certificates by adding a "null" string character to the certificate fields to fake out the browser. Moxie also added this null-termination attack to an existing hacking tool he developed.

"This is a wonderful example of what I'm talking about," Kaminsky says. "Moxie and I have the same core attack here -- he did this year what I did last year. We both went for the null" string attack, he says. Moxie was able to force a Firefox browser to download a code "update" over SSL with his phony digital certificate, Kaminsky says.

VeriSign's Callan says none of VeriSign's certificate brands or sub-bands have a domain containing a null character. "Marlinspike's presentation underscores the importance of such stringent issuance practices by CAs to ensure the integrity of online security," Callan says.

Ultimately, the answer is to move to DNSSEC, Kaminsky says. "We're going to have the DNS root signed [by DNSSEC] by the end of the year, so then we can build a new PKI with exclusion and delegation" capabilities, he says.

"Today, Dan Kaminsky revealed more important research that will surely serve to raise awareness on the need for ongoing enhancements to Internet infrastructure standards," VeriSign's Callan says.

Have a comment on this story? Please click "Discuss" below. If you'd like to contact Dark Reading's editors directly, send us a message.