Earlier this year, a Trojan infected a machine at software maker
Blackbaud. But rather than steal money or source code or customer
details, the attack targeted another valuable but often overlooked
piece of information: the company's private keys for signing its
software.
Blackbaud, which makes software to help nonprofits run their
businesses, discovered the theft when a security firm approached
the company and revealed it had encountered malware signed with the
company's private keys. Ironically, Blackbaud had already been
working to bolster its corporate security, says Jana Eggers, senior
vice president of products and marketing for the Charleston,
S.C.-based software company.
"Companies are very aware of their customer information, but
there are other pieces of information that need to be protected,"
Eggers says. "A virus can be tweaked to search for something
different, and a security certificate is not what you think of
protecting in the same way as customer information."
Blackbaud is not alone. Cybercriminals are increasingly
targeting developers' systems to steal the private keys used to
sign software. Programs signed with a digital certificate are
considered safer by the operating system and security software, and
the authors of malicious software have caught on.
Perhaps the most high-profile piece of malware to use digital
certificates is Stuxnet. The Trojan infected industrial control
systems in 2009 and 2010 and is widely considered to have been a
nation-state attack on Iran's nuclear processing facility. The
first stage of the Stuxnet attack used code signed by certificates
belonging to two Taiwanese companies to appear more innocuous to
security software.
In 2010, a version of the well-known Zeus banking Trojan used a
digital signature belonging to software security firm Kaspersky
Labs to lessen the chance of the program being identified as
malware. And a third attack in the same year used an Adobe flaw and
was signed with a certificate from a credit union.
"They are going right after the keys to the kingdom," says Jeff
Hudson, CEO at Venafi, a maker of enterprise key and certificate
management software. "They are not trying to siphon off pennies;
they are going right for the heart."
Security firm Symantec has documented a piece of malicious
software known as Infostealer.Nimkey that is designed to steal
private keys and keystrokes.
Thousands of certificates have been stolen and are being used by
malware, says Yuval Ben-Itzhak, chief technology officer for
security firm AVG. In a quarterly security report released on
Tuesday, AVG documented two attacks that used stolen certificates:
one belonging to Blackbaud and the other to German gaming company
GameForge Productions. GameForge did not respond to a request for
comment.
In the first half of 2011, three times as many certificates were
used to sign malware than the first half of 2010, according to
AVG's report. Companies need to better protect their certificates,
and security software should become more skeptical of signed code,
Ben-Itzhak says.
"The vendors are not rushing to revoke stolen certificates," he
says. "Blindly trusting certificates today is not a good
practice."
For large companies, certificate management systems such as
Venafi's can make sure that companies do not suffer from
certificates that accidentally expire or that are stored in
insecure places. Many times, developers just keep the private keys
needed to sign software on their work systems, Venafi's Hudson
says. "We advocate people to, number one, know what you've got on
your network," he says. "Number two, make sure that you separate
out private keys from pubic keys and be able to replace them
immediately, if you are compromised."
Treating digital certificates as valuable as the attackers is a
sentiment with which Blackbaud's Eggers can now certainly agree.
"More people need to be aware of the threat," she says.