Here’s how carefully concealed backdoor in fake AWS files escaped mainstream notice

aws-s3-object-multipart-copy, a legitimate JavaScript library for copying files using Amazon’s S3 cloud service. The fake files included all the code found in the legitimate library but added an additional JavaScript file named loadformat.js. That file provided what appeared to be benign code and three JPG images that were processed during package installation. One of those images contained code fragments that, when reconstructed, formed code for backdooring the developer device.

Growing sophistication

“We have reported these packages for removal, however the malicious packages remained available on npm for nearly two days,” researchers from Phylum, the security firm that spotted the packages, wrote. “This is worrying as it implies that most systems are unable to detect and promptly report on these packages, leaving developers vulnerable to attack for longer periods of time.”