Malware attacks on Docker Hub spread millions of malicious repositories

Cybersecurity researchers from JFrog recently discovered three malicious campaigns in Docker Hub – Docker’s cloud-based registry service for storing and sharing container images. These campaigns contained millions of repositories that pushed generic trojan malware to the developers.

The conclusion of JFrog’s findings is that with open-source repositories such as Docker Hub, keeping them clean of malware is an immensely difficult task.

As the researchers explained, Docker Hub repositories have two key aspects: the images (an application that can be updated and accessible through a fixed name), and the metadata (short descriptions and documentation in HTML format, which will be displayed on the repository’s main page).

Millions of bad repositories

“Usually, repository documentation aims to explain the purpose of the image and provide guidelines for its usage,” the researchers explained.

However, roughly 4.6 million repositories contained no Docker images, meaning they couldn’t be run using a Kubernetes cluster, or a Docker engine – they were practically useless. They just contained the overview page which tried to trick the developers into visiting phishing websites, or other pages hosting malicious code.

Of the 4.6 million repositories, 2.81 million were linked to three campaigns: “Downloader”, “eBook Phishing”, and “Website SEO”.

In terms of the number of malicious repositories, Downloader was the biggest one, amounting to almost 10% of the entire share (1,453,228 repositories). However, it did not have as many users (9,309) as, for example, Website SEO (194,699). The latter, however, only took up 1.4% of the share, having a “mere” 215,451 repositories.

With 7.1% of the share, eBook Phishing was the second, with 1,069,160 repositories. It only had 1,042 users though.

JFrog disclosed its findings to Docker, which prompted the project to remove the malicious repositories – 3.2 million of them.

“Unlike typical attacks targeting developers and organizations directly, the attackers in this case tried to leverage Docker Hub’s platform credibility, making it more difficult to identify the phishing and malware installation attempts,” JFrog said.

“Almost three million malicious repositories, some of them active for over three years highlight the attackers’ continued misuse of the Docker Hub platform and the need for constant moderation on such platforms.”