HTML Smuggling Technique Used to Attack European Entities

Over recent months, CPR (Check Point Research) monitored a Chinese threat actor attacking European Foreign Affairs ministries and embassies.

Check Point Research identified a broader trend of Chinese activity, specifically targeting European entities and their foreign policy.

While security analysts identified that threat actors were found using HTML Smuggling.

Since December 2022, this campaign has been ongoing and is probably a direct extension of a previously disclosed RedDelta campaign.

Several new delivery methods were used in this campaign to deploy a new variant of an implant, “PlugX,” that is linked to various Chinese threat actors.

HTML Smuggling Technique

In the SmugX campaign, HTML Smuggling is applied, leading to JavaScript or ZIP file downloads.

The lure themes primarily target the governmental ministries in Eastern Europe since they are mainly focused on European domestic and foreign policies.

Most documents featured diplomatic content, with some directly linked to China in multiple instances. The lures include:-

• A letter originating from the Serbian embassy in Budapest.
• A document stating the priorities of the Swedish Presidency of the Council of the European Union.
• An invitation to a diplomatic conference issued by Hungary’s Ministry of Foreign Affairs.
• An article about two Chinese human rights lawyers sentenced to more than a decade in prison.

A document called “China Tries to Block Prominent Uyghur Speaker at UN.docx,” was discovered by the security analysts during their analysis, and it was uploaded to VirusTotal.

Besides this, to access the following URL, the document uses a remote image technique, and it contains a single-pixel image that it keeps hidden from the user:-

• https://www[.]jcswcd[.]com/?wd=cqyahznz

It’s known as Pixel tracking, a common reconnaissance tool that logs the following information when the attackers’ server receives a request for the remote image:-

• IP address
• User-agent
• Access time

Infection Chains

In total, there are two infection chains that stem from an HTML file that stores the second stage in the Download folder as per the browser settings of the victim.

One chain deploys a malicious LNK file inside a ZIP file, while to fetch an MSI file from a remote server, the other chain employs JavaScript.

PlugX malware, used by Chinese threat actors since 2008, serves as the final payload, and it’s operated as a remote access tool (RAT) with a modular structure for flexible plugin integration.

For persistence, the PlugX payload duplicates and hides both the legitimate program and DLL in a newly created hidden directory.

Though none of the techniques employed in this campaign are unexplored, the blend of a wide range of tactics and infection chains with low detection rates allowed the threat actors to remain undetected for an extended period of time.

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