Chinese Lotus Blossom APT Targets Multiple Sectors with Sagerunex Backdoor

A sophisticated cyber espionage group known as Chinese Lotus Blossom APT, also referred to as Elise and Esile, has been actively targeting governments and industries in Asian countries using the Sagerunex backdoor variants. The Talos researchers have linked this China-backed Advanced Persistent Threat (APT) group to multiple campaigns against organizations in sectors such as government, manufacturing, telecommunications, and media.

The victims of these attacks are located in the Philippines, Vietnam, Hong Kong, and Taiwan. It is worth noting that the Lotus Blossom APT has been active since at least 2012 and has been using the Sagerunex backdoor since at least 2016.

New Variants of Sagerunex Backdoor

Talos observed the APT group using two new Sagerunex backdoor variants in attacks against telecom, media, government, and manufacturing sectors. These variants use cloud services like Dropbox, Twitter, and Zimbra for Command and Control (C2), replacing the original Virtual Private Server (VPS) method.

The new variants are designed to gather, encrypt, and exfiltrate target host information to a remote server controlled by the attacker. The Dropbox and X versions were used between 2018 and 2022, while the Zimbra version has been active since 2019. Detailed malware analysis reveals configuration and potential host paths.

Cloud-Based C2 Channels

The new variants of Sagerunex backdoor use cloud-based services like Dropbox, Twitter, and Zimbra as C2 channels to evade detection. The Beta version distinguished by debug strings uses Dropbox as a C2 channel, while another variant uses both Dropbox and Twitter for data exfiltration.

A third variant uses the Zimbra webmail service, employing the Zimbra API for data exfiltration via email drafts. Each variant implements various checks, such as time-based delays and system verifications, to maintain persistence.

Obfuscation Techniques

The malware's loader injects the backdoor into memory and uses encryption to obfuscate data. Additionally, the use of VMProtect obfuscates the malware code to evade antivirus detection. Talos identified specific file paths and configuration details, indicating that the malware has been active for years.

Attribution and Indicators of Compromise

Talos attributes recent campaigns to the Lotus Blossom group based on the use of the Sagerunex backdoor, an evolved version of Billbug's Evora. The three variants maintain the same core functionalities, supporting the attribution to Lotus Blossom due to consistent targeting patterns and TTPs.

The report includes Indicators of compromise (IOCs) for these attacks. You can follow Talos on Twitter: @securityaffairs and Facebook and Mastodon to stay up-to-date with the latest security news and updates.