Trojanized ESET Installers Deliver Kalambur Backdoor
🛡️ A Russia-aligned cluster tracked as InedibleOchotense impersonated Slovak vendor ESET in May 2025, sending spear-phishing emails and Signal messages to multiple Ukrainian organizations. Recipients were directed to domains such as esetsmart[.]com hosting a trojanized installer that deployed the legitimate ESET AV Remover alongside a C# backdoor dubbed Kalambur (aka SUMBUR). Kalambur leverages the Tor network for command-and-control and can install OpenSSH and enable RDP on port 3389 to facilitate remote access. ESET links the campaign to Sandworm sub-clusters and notes overlaps with activity reported by CERT-UA and EclecticIQ.
