The China-based Suckfly group has used nine stolen digital certificates to sign its malicious programs since 2014
An increasing number of cyberespionage groups are using stolen
code-signing certificates to make their hacking tools and malware look
like legitimate applications.
The latest example is a China-based
hacker group that has launched targeted attacks against government and
commercial organizations from around the world over the past two years.
The
group's activities were uncovered by researchers from Symantec in late
2015 when they detected a digitally signed hacking tool that was used in
an attack against one of the company's customers.
The tool, a Windows brute-force server message block (SMB) scanner,
was signed with a digital certificate that belonged to a South Korean
mobile software developer. This immediately raised red flags as a mobile
software company would have no reason to sign such an application.
Further
searches led to the identification of three additional hacking tools
that had been signed with the same certificate and had been used in an
attack against a U.S.-based health provider operating in India.
The Symantec researchers traced the attacks back to IP (Internet Protocol) addresses in Chengdu, China.
The
investigation ultimately led to the discovery of additional hacking
programs and malware used by the same group of attackers in the past two
years. Those programs had been signed with nine stolen digital
certificates belonging to companies from Seoul, South Korea.
Three
of the certificate owners were companies from the software industry,
three were from the video game industry, two from entertainment and
media sector and one from financial services sector.
"While
we do not know the exact circumstances of how the certificates were
stolen, the most likely scenario was that the companies were breached
with malware that had the ability to search for and extract certificates
from within the organization," the Symantec researchers said in a blog post Tuesday. "We have seen this capability built into a wide range of malware for a number of years now."
When
the certificates were discovered in late 2015 they were still valid and
their rightful owners didn't know that they had been stolen, even
though some of the certificates had been used to sign malware since
2014, the researchers said.
In addition to hacking tools, this
China-based hacker group, which Symantec has dubbed Suckfly, uses a
custom backdoor program that appears to have been designed specifically
for cyberespionage attacks. Symantec calls this malware program
Backdoor.Nidiran.
Suckfly is not the first group of attackers to digitally sign its malware. The Hidden Lynx and Winnti gangs, exposed in 2013, and the Black Vine
group, uncovered in 2015, are also known to have used stolen
code-signing certificates in their operations. More famously, the
Stuxnet cybersabotage worm that affected Iran's nuclear program had
components signed with several stolen certificates.
"Attackers are
taking the time and effort to steal certificates because it is becoming
necessary to gain a foothold on a targeted computer," the Symantec
researchers said. "Attempts to sign malware with code-signing
certificates have become more common as the Internet and security
systems have moved towards a more trust and reputation oriented model.
This means that untrusted software may not be allowed to run unless it
is signed."
By default, the latest versions of Apple's Mac OS X
only allow applications to run if they have been downloaded from the Mac
App Store or if they have been signed with a developer certificate
obtained from Apple. Windows will display User Account Control (UAC)
warnings for unsigned executable files that try to gain administrator
privileges.
Some security and application whitelisting products
can also treat files differently based on whether they are digitally
signed with a trusted certificate or not.
It's clear that digital
certificates, especially those used for code signing, have become
valuable targets for cybercriminals, so it is very important for
organizations who own such certificates to maintain strong cybersecurity
practices and store them in secure environments.