[TONESHELL](https://attack.mitre.org/software/S1239) is a custom backdoor that has been used since at least Q1 2021.(Citation: Palo Alto Unit42 STATELY TAURUS TONESHELL September 2023) [TONESHELL](https://attack.mitre.org/software/S1239) malware has previously been leveraged by Chinese affiliated actors identified as [Mustang Panda](https://attack.mitre.org/groups/G0129).(Citation: ATTACKIQ MUSTANG PANDA TONESHELL March 2023)(Citation: Zscaler)