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MalwareUsed by 2 actorsExploits 2 CVEs

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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EXPLOITED CVES

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.

2 CVES
CVE-2021-40444Microsoft MSHTML Remote Code Execution VulnerabilityExploited in the wild

Details on Exploited Vulnerabilities ... CVE-2021-40444 Microsoft Windows ... YARA Rules ... reference = “... PrintNightmare and MSHTML exploits” ... $cve2 = “CVE-2021-40444”

via cyfirma newscyfirma.com
CVE-2021-1675PrintNightmare / Windows Print Spooler RCE in CVE-2021-1675 contextExploited in the wild

Details on Exploited Vulnerabilities ... CVE-2021-1675 Microsoft Windows ... YARA Rules ... reference = “... PrintNightmare and MSHTML exploits” ... $cve1 = “CVE-2021-1675”

via cyfirma newscyfirma.com
THREAT ACTORS

Groups observed using it

2 distinct threat actors attributed by public researchers. Open in Mallory to see the full evidence chain and overlapping campaigns.

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Mustang Panda

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.

via the hacker newsthehackernews.com
UNK_SteadySplit

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.

via infosecurity magazineinfosecurity-magazine.com
MITRE ATT&CK

Techniques & procedures

34 distinct techniques documented for this family, organized by ATT&CK tactic.

Initial Access

1 technique
T1566.001Spearphishing AttachmentEvidence1

Typical attack chains involve the use of spear-phishing emails to drop malware families like PUBLOAD or TONESHELL.

Execution

7 techniques
T1047Windows Management InstrumentationEvidence1
TacticExecution
T1053Scheduled Task/JobEvidence1

“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.”

T1053.005Scheduled TaskEvidence3

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.

T1059Command and Scripting InterpreterEvidence1
TacticExecution

facilitate two active reverse shells in parallel... Yokai, a backdoor that sets up a reverse shell to execute arbitrary commands.

T1059.003Windows Command ShellEvidence3
TacticExecution

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.'

T1106Native APIEvidence1
TacticExecution

"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"

T1574.001DLLEvidence1

Persistence

5 techniques
T1053Scheduled Task/JobEvidence1

“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.”

T1053.005Scheduled TaskEvidence3

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.

T1112Modify RegistryEvidence1

Across the content, malware repeatedly 'adds Registry Run keys', 'creates Registry entries', 'modifies the Windows Registry', or 'overwrites registry keys' to maintain persistence.

T1543.003Windows ServiceEvidence1

“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.”

T1547.001Registry Run Keys / Startup FolderEvidence3

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.

T1053Scheduled Task/JobEvidence1

“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.”

T1053.005Scheduled TaskEvidence3

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.

T1055Process InjectionEvidence1

"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"

T1543.003Windows ServiceEvidence1

“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.”

T1547.001Registry Run Keys / Startup FolderEvidence3

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 techniques
T1027.007Dynamic API ResolutionEvidence1
TacticStealth
T1036MasqueradingEvidence1
TacticStealth

During the 2016 Ukraine Electric Power Attack, DLLs and EXEs with filenames associated with common electric power sector protocols were used to masquerade files.

T1055Process InjectionEvidence1

"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"

T1070.004File DeletionEvidence4
TacticStealth

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.'

T1140Deobfuscate/Decode Files or InformationEvidence3
TacticStealth

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.'

T1218.010Regsvr32Evidence2
TacticStealth

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.

T1218.013MavinjectEvidence1
TacticStealth
T1480.001Environmental KeyingEvidence1
TacticStealth
T1480.002Mutual ExclusionEvidence1
TacticStealth
T1497.001System ChecksEvidence1

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.

T1497.002User Activity Based ChecksEvidence1
T1574.001DLLEvidence1
T1622Debugger EvasionEvidence1
T1678Delay ExecutionEvidence1
TacticStealth

Defense Impairment

2 techniques
T1112Modify RegistryEvidence1

Across the content, malware repeatedly 'adds Registry Run keys', 'creates Registry entries', 'modifies the Windows Registry', or 'overwrites registry keys' to maintain persistence.

T1553.002Code SigningEvidence1

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 techniques
T1057Process DiscoveryEvidence1
TacticDiscovery

The 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.

T1082System Information DiscoveryEvidence2
TacticDiscovery

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."

T1497.001System ChecksEvidence1

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.

T1497.002User Activity Based ChecksEvidence1
T1622Debugger EvasionEvidence1
T1680Local Storage DiscoveryEvidence1
TacticDiscovery

Collection

2 techniques
T1113Screen CaptureEvidence1
T1560Archive Collected DataEvidence2

Listeners.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.

T1071.001Web ProtocolsEvidence3

The 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.

T1095Non-Application Layer ProtocolEvidence1
T1105Ingress Tool TransferEvidence1

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.

T1219Remote Access ToolsEvidence1

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.

INDICATORS OF COMPROMISE

IOCs tracked for this family

2 indicators attributed across vendor reports, sandbox runs, and researcher write-ups. Full values are available in Mallory.

View more in app
Network
2 tracked

IPs, domains, and DNS infrastructure linked to this family.

TypeValueLatest sighting
domain●●●●●●●●●●●●View more in app5 months ago
domain●●●●●●●●●●●●View more in app5 months ago
What this page doesn’t show

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IOC matching2

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Threat actor attribution2

Named campaigns wielding this family, with evidence pinned to each claim.

Exploited vulnerabilities2

CVEs this family uses for access and lateral movement.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

MITRE ATT&CK mapping34

Every documented technique, ranked by evidence weight.

Researcher chatter

Reddit, Mastodon, and CTI community discussion around this family.