Malware downloaded from PyPI 41,000 times was surprisingly stealthy

Enlarge (credit: Getty Images)

PyPI—the open source repository that both large and small organizations use to download code libraries—was hosting 11 malicious packages that were downloaded more than 41,000 times in one of the latest reported such incidents threatening the software supply chain.

JFrog, a security firm that monitors PyPI and other repositories for malware, said the packages are notable for the lengths its developers took to camouflage their malicious code from network detection. Those lengths include a novel mechanism that uses what’s known as a reverse shell to proxy communications with control servers through the Fastly content distribution network. Another technique is DNS tunneling, something that JFrog said it had never seen before in malicious software uploaded to PyPI.

A powerful vector

“Package managers are a growing and powerful vector for the unintentional installation of malicious code, and as we discovered with these 11 new PyPI packages, attackers are getting more sophisticated in their approach, Shachar Menashe, senior director of JFrog research, wrote in an email. “The advanced evasion techniques used in these malware packages, such as novel exfiltration or even DNS tunneling (the first we’ve seen in packages uploaded to PyPI) signal a disturbing trend that attackers are becoming stealthier in their attacks on open source software.”