Go Module Mirror served backdoor to devs for 3+ years

A mirror proxy Google runs on behalf of developers of the Go programming language pushed a backdoored package for more than three years until Monday, after researchers who spotted the malicious code petitioned for it to be taken down twice.

The service, known as the Go Module Mirror, caches open source packages available on GitHub and elsewhere so that downloads are faster and to ensure they are compatible with the rest of the Go ecosystem. By default, when someone uses command-line tools built into Go to download or install packages, requests are routed through the service. A description on the site says the proxy is provided by the Go team and “run by Google.”

Caching in

Since November 2021, the Go Module Mirror has been hosting a backdoored version of a widely used module, security firm Socket said Monday. The file uses “typosquatting,” a technique that gives malicious files names similar to widely used legitimate ones and plants them in popular repositories. In the event someone makes a typo or even a minor variation from the correct name when fetching a file with the command line, they land on the malicious file instead of the one they wanted. (A similar typosquatting scheme is common with domain names, too.)

The malicious module was named boltdb-go/bolt, a variation of widely adopted boltdb/bolt, which 8,367 other packages depend on to run. The malicious package first appeared on GitHub. The file there was eventually reverted back to the legitimate version, but by then, the Go Module Mirror had cached the backdoored one and stored it for the next three years.

“The success of this attack relied on the design of the Go Module Proxy service, which prioritizes caching for performance and availability,” Socket researchers wrote. “Once a module version is cached, it remains accessible through the Go Module Proxy, even if the original source is later modified. While this design benefits legitimate use cases, the threat actor exploited it to persistently distribute malicious code despite subsequent changes to the repository.”