TONESHELL
TONESHELL is a bespoke backdoor associated with the China-aligned threat actor Mustang Panda, also referenced in reporting tied to HoneyMyte, Stately Taurus, and UNK_SteadySplit-related activity. It was first publicly documented by Trend Micro in November 2022 and has since appeared in multiple Mustang Panda intrusion sets, including campaigns targeting an unspecified organization in Myanmar and broader espionage activity in Asia and Southeast Asia. Reporting also notes technical overlaps between TONESHELL and Bookworm, including similar debug paths and infrastructure, suggesting related development lineage or operational synergy.
TONESHELL is commonly delivered through DLL side-loading using legitimate signed executables, and some campaigns abused valid legitimate digital signatures and certificates to evade detection. It has also been executed via regsvr32.exe calling DLLRegisterServer. Its primary role is to download next-stage payloads on infected hosts, though observed variants provide broader backdoor capability. Reported functionality includes acting as a reverse shell, downloading DLLs from command-and-control and injecting them into legitimate processes such as svchost.exe, downloading files, executing commands through a custom TCP-based protocol, stealing files, downloading data, and running remote commands. TONESHELL has utilized TCP-based reverse shells and has facilitated inter-process communication between DLL components via pipes, including use of two anonymous pipes to write to stdin and read from stdout and stderr.
For persistence, TONESHELL has created scheduled tasks. For collection and exfiltration support, it has used WinRAR rar.exe to archive files for exfiltration. Recent reporting states updated TONESHELL variants modified their FakeTLS command-and-control protocol and changed methods for creating and storing client identifiers. Zscaler identified three variants with differing sophistication: a simple reverse shell; a variant that downloads DLLs and injects them into legitimate processes; and a variant that downloads files and creates a subprocess to execute commands over a custom TCP-based protocol.
TONESHELL is strongly linked to Mustang Panda operations and is described as a known backdoor associated with that cluster since late 2022. It has also been cited as one of the main tools in campaigns attributed to Stately Taurus, and prior research identified a TONESHELL C2 IP embedded in LNK file paths used in TA416 campaigns, indicating historical overlap between TA416 and UNK_SteadySplit. Related reporting also references rootkit-enabled activity used to hide or inject updated TONESHELL malware.
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Vulnerabilities exploited
2 CVEs Mallory has correlated with this family across public research and vendor advisories. Each row links to the full Mallory page for that vulnerability.
Details on Exploited Vulnerabilities ... CVE-2021-40444 Microsoft Windows ... YARA Rules ... reference = “... PrintNightmare and MSHTML exploits” ... $cve2 = “CVE-2021-40444”
Details on Exploited Vulnerabilities ... CVE-2021-1675 Microsoft Windows ... YARA Rules ... reference = “... PrintNightmare and MSHTML exploits” ... $cve1 = “CVE-2021-1675”
Groups observed using it
2 distinct threat actors attributed by public researchers. Open in Mallory to see the full evidence chain and overlapping campaigns.
The China-aligned threat actor known as Mustang Panda has been observed using an updated version of a backdoor called TONESHELL... TONESHELL was first publicly documented by Trend Micro way back in November 2022... Typically executed via DLL side-loading, its primary responsibility is to download next-stage payloads on the infected host.
Prior research by Trend Micro had identified technical overlaps between TA416 and UNK_SteadySplit, most notably through a UNK_SteadySplit TONESHELL command-and-control (C2) IP address embedded in a filepath within two LNK files used in TA416 campaigns.
Techniques & procedures
34 distinct techniques documented for this family, organized by ATT&CK tactic.
Initial Access
1 techniqueTypical attack chains involve the use of spear-phishing emails to drop malware families like PUBLOAD or TONESHELL.
Execution
7 techniques“Sandworm Team leveraged Scheduled Tasks through a Group Policy Object (GPO) to execute CaddyWiper at a predetermined time.” / “APT29 used scheduler and schtasks to create new tasks on remote host as part of their lateral movement… updating an existing legitimate task to execute their tools and then returned the scheduled task to its original configuration.”
During the 2022 Ukraine Electric Power Attack, Sandworm Team leveraged Scheduled Tasks through a Group Policy Object (GPO) to execute CaddyWiper at a predetermined time.
facilitate two active reverse shells in parallel... Yokai, a backdoor that sets up a reverse shell to execute arbitrary commands.
Many entries explicitly state malware 'can create a reverse shell' or 'launch a remote shell,' including 4H RAT, AuditCred, BLACKCOFFEE, Carbanak, DarkComet, Exaramel for Windows, PlugX, QuasarRAT, and ZxShell. | The content repeatedly describes use of cmd.exe, cmd /c, Windows command shell, and xp_cmdshell to execute commands, run payloads, launch binaries, perform reconnaissance, persistence, cleanup, and ransomware actions. Examples include: 'Sandworm Team used the xp_cmdshell command in MS-SQL', 'APT41 used cmd.exe /c to execute commands on remote machines', and many malware families 'can use cmd.exe to execute commands on a compromised host.'
"BOOKWORM ... execution on the heap is initiated through callback function of legitimate API functions such as EnumChildWindows or EnumSystemLanguageGroupsA"; "CLAIMLOADER ... run its shellcode through the callback function"; "PUBLOAD stager leveraged Windows API functions with callback ... to bypass anti-virus monitoring"
Persistence
5 techniques“Sandworm Team leveraged Scheduled Tasks through a Group Policy Object (GPO) to execute CaddyWiper at a predetermined time.” / “APT29 used scheduler and schtasks to create new tasks on remote host as part of their lateral movement… updating an existing legitimate task to execute their tools and then returned the scheduled task to its original configuration.”
During the 2022 Ukraine Electric Power Attack, Sandworm Team leveraged Scheduled Tasks through a Group Policy Object (GPO) to execute CaddyWiper at a predetermined time.
Across the content, malware repeatedly 'adds Registry Run keys', 'creates Registry entries', 'modifies the Windows Registry', or 'overwrites registry keys' to maintain persistence.
“Sandworm Team used an arbitrary system service to load at system boot for persistence for Industroyer… replaced the ImagePath registry value of a Windows service with a new backdoor binary… [multiple groups/malware] creating a service / installing as a service / modifying service configurations for persistence.”
The content repeatedly describes malware and threat actors establishing persistence by adding values under HKCU/HKLM\Software\Microsoft\Windows\CurrentVersion\Run or RunOnce, and by placing executables, scripts, .lnk files, or .bat files in the Windows Startup folder.
Privilege Escalation
5 techniques“Sandworm Team leveraged Scheduled Tasks through a Group Policy Object (GPO) to execute CaddyWiper at a predetermined time.” / “APT29 used scheduler and schtasks to create new tasks on remote host as part of their lateral movement… updating an existing legitimate task to execute their tools and then returned the scheduled task to its original configuration.”
During the 2022 Ukraine Electric Power Attack, Sandworm Team leveraged Scheduled Tasks through a Group Policy Object (GPO) to execute CaddyWiper at a predetermined time.
"APT37 leverages the Windows API calls: VirtualAlloc(), WriteProcessMemory(), and CreateRemoteThread() for process injection"; "IcedID has called ZwWriteVirtualMemory... ZwQueueApcThread... to inject itself into a remote process"; "Havoc can use NtAllocateVirtualMemory and NtCreateThreadEx to aid process injection"
“Sandworm Team used an arbitrary system service to load at system boot for persistence for Industroyer… replaced the ImagePath registry value of a Windows service with a new backdoor binary… [multiple groups/malware] creating a service / installing as a service / modifying service configurations for persistence.”
The content repeatedly describes malware and threat actors establishing persistence by adding values under HKCU/HKLM\Software\Microsoft\Windows\CurrentVersion\Run or RunOnce, and by placing executables, scripts, .lnk files, or .bat files in the Windows Startup folder.
Stealth
14 techniquesDuring the 2016 Ukraine Electric Power Attack, DLLs and EXEs with filenames associated with common electric power sector protocols were used to masquerade files.
"APT37 leverages the Windows API calls: VirtualAlloc(), WriteProcessMemory(), and CreateRemoteThread() for process injection"; "IcedID has called ZwWriteVirtualMemory... ZwQueueApcThread... to inject itself into a remote process"; "Havoc can use NtAllocateVirtualMemory and NtCreateThreadEx to aid process injection"
The content repeatedly describes adversaries and malware deleting files, directories, droppers, scripts, logs, archives, staged data, and other artifacts from compromised systems, e.g., 'APT29 has used SDelete to remove artifacts from victim networks' and 'Lazarus Group malware has deleted files in various ways, including "suicide scripts" to delete malware binaries from the victim.'
The content repeatedly describes malware and threat actors decoding, decrypting, or deobfuscating payloads, strings, configuration data, commands, and C2 traffic prior to execution or use, e.g., 'APT28 macro uses the command certutil -decode to decode contents of a .txt file storing the base64 encoded payload' and 'Action RAT can use Base64 to decode actor-controlled C2 server communications.'
AppleSeed can call regsvr32.exe for execution. APT19 used Regsvr32 to bypass application control techniques. APT32 created a Scheduled Task/Job that used regsvr32.exe to execute a COM scriptlet that dynamically downloaded a backdoor and injected it into memory. ... Raspberry Robin uses regsvr32.exe execution without any command line parameters for command and control requests to IP addresses associated with Tor nodes.
Several entries describe malware examining running processes to determine if a debugger, sandbox, virtual environment, or analysis/security tools are present, such as AsyncRAT checking for a debugger, RogueRobin enumerating Wireshark and Sysinternals processes, and P8RAT checking for processes associated with virtual environments.
Defense Impairment
2 techniquesAcross the content, malware repeatedly 'adds Registry Run keys', 'creates Registry entries', 'modifies the Windows Registry', or 'overwrites registry keys' to maintain persistence.
The content repeatedly describes threat actors and malware using valid, stolen, forged, self-signed, or abused code-signing certificates to sign malware and appear legitimate, including examples such as AppleJeus using a valid digital signature from Sectigo, APT41 leveraging code-signing certificates, FIN7 signing Carbanak payloads, and SUNBURST being digitally signed by SolarWinds.
Discovery
6 techniquesThe content repeatedly describes malware and threat actors obtaining lists of running processes, using utilities such as tasklist, ps, WMI, Get-Process, CreateToolhelp32Snapshot, EnumProcesses, and similar APIs/commands to enumerate active processes on victim systems.
The content repeatedly describes malware and threat actors collecting host details such as OS version, hostname, architecture, CPU, memory, BIOS, domain, language, and other configuration data; e.g., "APT41 uses multiple built-in commands such as systeminfo and net config Workstation to enumerate victim system basic configuration information."
Several entries describe malware examining running processes to determine if a debugger, sandbox, virtual environment, or analysis/security tools are present, such as AsyncRAT checking for a debugger, RogueRobin enumerating Wireshark and Sysinternals processes, and P8RAT checking for processes associated with virtual environments.
Collection
2 techniquesListeners.bat: On some occasions the attackers used a batch file named Listeners.bat to archive files for exfiltration... the attacker executed rar.exe remotely via SMB. Next, they tried to iterate and archive all drives from A-Z on remote machines.
Command and Control
4 techniquesThe content repeatedly describes threat actors, malware, and campaigns using HTTP and/or HTTPS for command and control, including examples such as BlackEnergy communicating with C2 over HTTP POST requests and many other families using HTTP/S for C2.
its primary responsibility is to download next-stage payloads on the infected host... PUBLOAD... is also capable of downloading shellcode payloads via HTTP POST requests from a command-and-control (C2) server.
4H RAT has the capability to create a remote shell. AuditCred can open a reverse shell on the system to execute commands. PlugX allows actors to spawn a reverse shell on a victim. QuasarRAT can launch a remote shell to execute commands on the victim’s machine.
IOCs tracked for this family
2 indicators attributed across vendor reports, sandbox runs, and researcher write-ups. Full values are available in Mallory.
IPs, domains, and DNS infrastructure linked to this family.
Recent activity
67 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
Referenced as part of Mustang Panda's malware evolution alongside LOTUSLITE and other tooling.
A named malware/tool repeatedly deployed by the Mustang Panda cluster in recent attacks.
A malware/backdoor family referenced as part of infrastructure overlap analysis linking TA416 and UNK_SteadySplit, specifically via a TONESHELL C2 IP address embedded in TA416 campaign artifacts.
A custom malware family used by UNK_SteadySplit in phishing campaigns; the content does not provide further technical detail here.
The version that knows your environment.
Match every observed IP, domain, and hash against your live telemetry.
Named campaigns wielding this family, with evidence pinned to each claim.
CVEs this family uses for access and lateral movement.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Every documented technique, ranked by evidence weight.
Reddit, Mastodon, and CTI community discussion around this family.