Duqu May Have Targeted Certificate Authorities for Encryption Keys

Further analysis of the latest version of Stuxnet indicates the Duqu worm may be attacking certificate authorities in order to obtain legitimate keys to masquerade as a trusted application.

As Symantec continues its analysis of Duqu, the latest malware targeting industrial control firms and based on the Stuxnet worm, other security researchers believe that certificate authorities are among the affected victims.

Symantec posted its preliminary analysis of the Duqu worm on Oct. 18. Duqu's focus appears to be on industrial control systems, but unlike Stuxnet, its goal appears to be information gathering and not disabling hardware. However, a pair of researchers from McAfee noted that the team behind Duqu may have compromised certificate authorities along the way.

McAfee researchers Guilherme Venere and Peter Szor believe that Duqu was created for espionage and to launch targeted attacks against certificate authorities. While Symantec had noted that several companies in Europe had been hit by Duqu, the Symantec Security Response team had not provided any details on the victims or the kind of information that had been obtained.

Based on their own analysis, McAfee's Venere and Szor claimed Duqu had been used in "professional, targeted attacks" against various certificate authorities in southern Europe, Middle East, parts of Asia and Africa.

"It is highly likely that this key, just like the previous two known cases, was not really stolen from the actual companies, but instead directly generated in the name of such companies at a CA as part of a direct attack," wrote Venere and Szor, noting that Stuxnet had used two digital certificates belonging to companies in Taiwan, as well.

McAfee Labs advised Certificate Authorities to "carefully verify" their systems to ensure they weren't compromised by Duqu or other "variations." The digital certificate used by Duqu belonged to a Taiwanese company, C-Media Electronics, according to McAfee. It was most likely not stolen, but was legitimately issued by a compromised CA.

The certificate in question was revoked on Oct. 14 by VeriSign, the certificate authority recently acquired by Symantec. However, based on its internal investigation, Symantec said the private key used for the certificates had been stolen from its customers. VeriSign had not been tricked into issuing certificates to attackers. The company used "correct processes" to authenticate and verify the certificate was being requested by a legitimate customer, according to Symantec.

"At no time were Symantec's roots and intermediate CAs at risk, nor were there any issues with any CA, intermediate, or other VeriSign or Thawte brands of certificates," Symantec said.

The rogue SSL certificate was used to authenticate itself and sign Duqu's driver files, according to Symantec's analysis. This allowed Duqu to act as a trusted application within the network and communicate with other systems and applications because its components had been signed by a "legitimate" certificate, Jeff Hudson, CEO of Venafi, told eWEEK.

Organizations must maintain a complete inventory of all certificates issued by certificate authorities, monitor them, and know which ones are within policy. That way, administrators will know which ones aren't compliant and revoke them, Hudson said.

IT departments should be investing in a "solid logging infrastructure" to notice connections to unknown, foreign hosts, Bill Roth, CMO of LogLogic, told eWEEK. "People who do not monitor their networks with a log management infrastructure are like the homeowner who buys fake surveillance cameras for their house...and still gets ripped off," Roth said.

It's not just logging, as organizations should have a "mix of tools" to detect and block suspicious activity, Jason Lewis, CTO of Lookingglass, told eWEEK. The mix can include a Web proxy to control what sites employees are accessing, a firewall and intrusion prevention system can block malicious traffic, and two-factor authentication is better at securing accounts and services than just passwords, said Lewis.

"Using all of these elements together increases the likelihood of catching malicious activity quickly," Lewis said.