[Small Sieve](https://attack.mitre.org/software/S1035) is a Telegram Bot API-based Python backdoor that has been distributed using a Nullsoft Scriptable Install System (NSIS) Installer; it has been used by [MuddyWater](https://attack.mitre.org/groups/G0069) since at least January 2022.(Citation: DHS CISA AA22-055A MuddyWater February 2022)(Citation: NCSC GCHQ Small Sieve Jan 2022) Security researchers have also noted [Small Sieve](https://attack.mitre.org/software/S1035)'s use by UNC3313, which may be associated with [MuddyWater](https://attack.mitre.org/groups/G0069).(Citation: Mandiant UNC3313 Feb 2022)