Microsoft Product Flaws Make Net Dangerous, Experts Say
(01/23/98; 4:53 p.m. EST)
By Douglas Hayward, TechWeb

Flaws in the security of Microsoft's Internet products allow malicious hackers to steal users' private encryption keys and impersonate their victims, security experts said.

The flaws are so serious that one expert advises users not to surf the Web until a fix is found.

A security advisory note circulated this week by Peter Gutmann, a security expert in New Zealand, said that private encryption keys can easily be stolen from the hard disks of machines whose users are surfing the Web, thanks to flaws in several Microsoft products, including the Internet Explorer browser and the Internet Information Server package.

Private encryption keys are software codes that are used to encrypt information. They are used to create the digital version of personal signatures. These "digital signatures" are used to establish people's identities in online transactions.

"I would say it was a fairly important security flaw," Gutmann told TechWeb. "At the moment there is no defense against the problem."

Gutmann's advisory note describes the security holes in detail and has been circulated on Internet newsgroups since Wednesday. The note said that although private keys are themselves stored in an encrypted form, they can easily be decrypted and used by malicious hackers who can then use them to impersonate their victims and to steal personal data -- including passwords.

The problem, according to Gutmann, is that the file formats used to protect users' private encryption keys are flawed, and a flaw in the cryptography programming interfaces used by Microsoft means that many keys can be taken from a user's hard disk just by asking for them.

The security holes can easily be exploited thanks to flaws in Internet Explorer, which allow malicious software code hidden on Websites to read the content of users' hard drives when they visit the sites, Gutmann said.

"As a result of these flaws, no Microsoft Internet product is capable of protecting a user's keys from hostile attack," Gutmann said. A victim can have their private keys sucked off their machine and the encryption that "protects" it broken at a remote site without their knowledge, he said.

Representatives of Microsoft were not immediately available to comment.

"Once an attacker has obtained a user's private key in this manner, they have effectively stolen their digital identity, and can use it to digitally sign contracts and agreements, to recover every encryption session key it has ever protected in the past and will ever protect in the future, to access private and confidential email, and so on," he said.

The ease with which this attack can be carried out represents a critical weakness that compromises all other encryption components on Web servers and browsers, Gutmann said. "Once the private key is compromised, all security services which depend on it are also compromised," he said.

The flaws identified by Gutmann "can cause all sorts of interesting and menacing security situations," said Rop Gonggrijp, a Dutch former hacker who now works for an Internet service provider. "No one should operate a Windows 95 or NT machine connected to the Net without at least being behind a firewall and vaguely knowing someone who has a clue or two about security," Gonggrijp said.

"I find it particularly annoying that the Microsoft code has so very many weaknesses in the storage of keys," said Neil Barrett, a former hacker who is now a senior researcher and consultant with Groupe Bull. "Microsoft seem hell-bent on repeating very many of the problems originally suffered by Unix almost 20 years ago," Barrett said.

Microsoft should issue an immediate patches to cover the weaknesses in Internet Explorer which allow malicious code hidden on a Website to interrogate users' hard disks, Gutmann said. The company should also begin tackling the fundamental weaknesses in its protection of private keys, he added.

Gutmann said he was not being irresponsible by circulating details of the security flaws.

" I think anyone who has the knowledge to make use of the weaknesses would be able to figure them out for themselves, even if I hadn't published the details," he said. "And if I hadn't circulated them, everyone else would be unaware that a problem exists."