China-linked APT Billbug breached a certificate authority in Asia

A suspected China-linked APT group breached a digital certificate authority in Asia as part of a campaign aimed at government agencies since March 2022.

State-sponsored actors compromised a digital certificate authority in a country in Asia as part of a cyber espionage campaign aimed at multiple government agencies in the region, Symantec warns.

Symantec attributes the attack to a China-linked cyberespionage group tracked as Billbug (aka Lotus Blossom, Thrip). The attribution is based on the use of tools previously attributed to this APT group.

In 2019 Symantec researchers reported that the group was using the backdoors Hannotog (Backdoor.Hannotog) and Sagerunex (Backdoor.Sagerunex), which were both used in the recent campaign.

“The victims in this campaign included a certificate authority, as well as government and defense agencies.” reads the report published by Symantec. “All the victims were based in various countries in Asia. Billbug is known to focus on targets in Asian countries. In at least one of the government victims, a large number of machines on the network were compromised by the attackers.”

The compromise of a certificate authority could allow attackers to release valid code-signing certificates that could be used to sign malware to avoid detection. Compromised certificates can also be used to intercept HTTPS traffic. 

The good news is that Symantec has seen no evidence to suggest the attackers were able to compromise digital certificates. The security firm notified the certificate authority of the malicious activity.

The campaign has been ongoing since at least March 2022.

The analysis of the attack chain suggests that the attackers are exploiting public-facing applications to gain initial access to victim networks.

The threat actors make large use of dual-use and living-off-the-land tools, as well as custom malware. Below is a list of tools used by this APT group:

• AdFind – A publicly available tool that is used to query Active Directory. It has legitimate uses but is widely used by attackers to help map a network.
• Winmail – Can open winmail.dat files.
• WinRAR – An archive manager that can be used to archive or zip files – for example, prior to exfiltration.
• Ping – A tool that is freely available online that can allow users to determine if a specific location on a network is responding.
• Tracert – A network tool that can be used to determine the “path” packets take from one IP address to another. It provides the hostname, IP address, and the response time to a ping.
• Route – A path for sending packets through the internet network to an address on another network.
• NBTscan – Open-source command-line NetBIOS scanner.
• Certutil – Microsoft Windows utility that can be used for various malicious purposes, such as to decode information, to download files, and to install browser root certificates.
• Port Scanner – Allows an attacker to determine what ports are open on a network and could potentially be used to send and receive data.

The APT group also used an open source multi-level proxy tool called Stowaway to proxy external traffic to the intranet.

Cobalt Strike, which is a penetration testing framework, is considered commodity malware by many due to how often it is used by malicious actors.

“The targeting of the government victims is most likely driven by espionage motivations, with the certificate authority likely targeted in order to steal legitimate digital certificates, as mentioned in the introduction.” the researchers concluded. “The ability of this actor to compromise multiple victims at once indicates that this threat group remains a skilled and well-resourced operator that is capable of carrying out sustained and wide-ranging campaigns,”

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Pierluigi Paganini

(SecurityAffairs – hacking, certificate authority)

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