Comodo's SSL Certification Attack Only One Step in a Larger Attack

The attack that resulted in valid SSL certificates being issued for Microsoft, Google, Yahoo, Skype and Mozilla sites was only a step in a multilayered attack to steal information or spread malware, security experts say.

The Secure Sockets Layer certificates that were issued fraudulently for five popular Websites were only a step in a multipronged attack by those aiming to steal information or distribute malware, according to security experts.

Attackers impersonating a Comodo Security partner managed to request nine valid digital certificates for seven domains belonging to popular Websites, including Microsoft, Google, Yahoo and Skype, said Comodo Security on March 23. The certificates were revoked immediately and Comodo has not noticed any attempts to use the certificates.

While it's worrying that attackers were able to obtain a trusted certificate for a domain not under their control, it was only a small step in a larger attack, Brian Trzupek, Trustwave's vice president of managed identity and SSL, told eWEEK. Even with the certificates in hand, they would have still needed to tamper with the domain name server infrastructure to direct users to the malicious site holding the fraudulent certificate before they could have done any harm, according to Trzupek.

According to Comodo's incident report, attackers requested nine certificates, but definitely received only one before the account was suspended. Comodo was not clear whether the attackers ever received the remaining certificates. The March 15 breach was detected fairly quickly, so by the time the attackers got around to testing one of the certificates, it had already been revoked, according to Comodo.

The first step in this complicated attack required attackers to somehow compromise a Comodo trusted partner in Southern Europe, Comodo said. While Comodo didn't specify the nature of the data breach, the partner had several login credentials to other online accounts stolen, as well, Comodo wrote in its blog post.

"It is likely that this cert type was combined with another attack vector to allow the attacker to gain access to the certificate," Trzupek said.

The certificates themselves were not the ultimate goal. One of the domains the attacker targeted was the Mozilla Firefox add-on update server. Once users were redirected to the malicious site, the attackers could have injected arbitrary code into the Web browser or conned users looking for Firefox plug-ins that downloaded Trojans or key-loggers from the fraudulent site, Trzupek said. That would have been the final payoff for the attackers, whether it's gaining access to financial accounts, data theft or compromising the host machine, Trzupek said.

Comodo also noted that the targeted domains would have been of "greatest use" to a government attempting surveillance of Internet use by dissidents, especially considering the recent turmoil in North Africa and the Persian Gulf region.

The issued SSL certificate is generally a "domain validation only" certificate, Trzupek said. These types of certificates usually undergo automated validation where human review does not occur, he said.

While this attack affected only the Comodo certificate authority and not others, this could have had bigger implications as all Web browsers that trust Comodo as a root authority would have been affected, said Trzupek. For example, Comodo is included as a trusted root certification authority on all supported versions of Microsoft Windows.

Users should make sure to be on modern and fully updated browsers, as well as ensure they have not disabled CRL (Certificate Revocation List) or OCSP (Online Certificate Status Protocol) security checks in the browser.