Description

A rising and sophisticated kind of voice phishing (vishing) known as "Letscall" that targets individuals throughout South Korea in a multi-step attack to fool victims into installing malicious applications from a fake Google Play Store website has drawn the attention of researchers. A downloader program prepares the victim's device for the installation of malicious malware, which allows incoming calls to be rerouted to the attackers' call center. What distinguishes "Letscall" is its use of clever evasive strategies. During the initial download, the malware employs Tencent Legu and Bangcle (SecShell) obfuscation. Later stages leverage complicated naming structures in ZIP file folders and deliberately corrupt the manifest to mislead and bypass security measures. Further, "Letscall" makes use of cutting-edge technologies such as voice over IP (VOIP) and WebRTC to help with voice traffic routing and also employs the Session Traversal Utilities for NAT (STUN) and Traversal Using Relays around NAT (TURN) protocols, as well as Google STUN servers, to enable high-quality phone or video conversations while bypassing NAT and firewall restrictions.