Cisco Talos Intelligence Group - Comprehensive Threat Intelligence: Nibiru ransomware variant decryptor

Weak encryption

The Nibiru ransomware is a .NET-based malware family. It traverses directories in the local disks, encrypts files with Rijndael-256 and gives them a .Nibiru extension. Rijndael-256 is a secure encryption algorithm. However, Nibiru uses a hard-coded string "Nibiru" to compute the 32-byte key and 16-byte IV values. The decryptor program leverages this weakness to decrypt files encrypted by this variant.  

Ransomware

Nibiru ransomware is a poorly executed ransomware variant. It traverses directories and encrypts files with Rijndael-256. The files are given an extension, .Nibiru, after encryption. The ransomware targets numerous common file extensions but skips critical directories like Program Files, Windows and System Volume Information. Extensions targeted by Nibiru: .doc, .docx, .xls, .xlsx, .ppt, .pptx, .jpg, .jpeg, .png, .psd, .txt, .zip, .rar, .html, .php, .asp, .aspx, .mp4, .avi, .3gp, .wmv, .MOV, .mp3, .wav, .flac, .wma, .mov, .raw, .apk, .encrypt, .crypted, .ahok, .cs, .vb.  

Compiling

We've tested the Nibiru Ransomware Variant Decryptor tusing Visual Studio Community 2019, version 16.7.6 on Windows 10 running .NET Framework, version 4.8.03752. No additional packages are necessary to compile. You can download the decryptor over at the Talos GitHub. Example hash: e0a681902f4f331582670e535a7d1eb3d6eff18d3fbed3ffd2433f898219576f