China-linked APT group utilizes HTML smuggling in targeted attacks against European ministries and embassies, according to cybersecurity firm Check Point. The campaign, known as SmugX and ongoing since December 2022, involves the delivery of a new variant of the PlugX remote access trojan using the evasive technique of HTML smuggling, which hides malicious payloads within HTML documents. The attackers specifically targeted government entities in Europe, focusing on foreign and domestic policy organizations.
By employing spear-phishing techniques, the threat actors enticed victims to download JavaScript or ZIP files containing encoded payloads.
Upon opening the malicious HTML documents, the embedded payload is decoded and saved to a JavaScript blob, utilizing functions like createObjectURL and msSaveOrOpenBlob to simulate user interactions and initiate file downloads. The campaign, associated with Chinese APT groups RedDelta and Mustang Panda, aimed to infect diplomats and government entities in countries such as Czechia, Hungary, Slovakia, the U.K., and Ukraine.
The attackers leveraged lures such as a letter from the Serbian embassy, documents related to the Swedish Presidency of the Council of the European Union, and invitations to diplomatic conferences, among others.
The sophisticated attack chain relied on DLL side-loading techniques to deliver the PlugX RAT. Notably, the campaign introduced the increased use of RC4 encryption for configuration, and the threat actors attempted to erase evidence of their activities by dispatching a batch script named del_RoboTask Update.bat, which removed legitimate executables, the PlugX loader DLL, and associated registry keys.
While the attribution to RedDelta or Mustang Panda is based on similarities in infrastructure, deployment methods, victimology, and lure tactics, there is insufficient evidence to link the SmugX campaign directly to the Camaro Dragon group.
