Detect LNK Icon Smuggling in Sumo Logic CSE
Adversaries abuse Windows shortcut (.LNK) files to smuggle malicious payloads past content filters. LNK files contain metadata fields including an icon location field (IconEnvironmentDataBlock) designed to specify an icon file path. Adversaries exploit this field to reference external URLs that trigger payload downloads when the LNK is invoked. They also abuse the LNK target path field to embed interpreter commands with obfuscated arguments, often padding target fields with extra spaces to hide the malicious portion from casual inspection. Threat actors including Kimsuky, Gamaredon Group, Mustang Panda, and TONESHELL malware have weaponized LNK files with spoofed PDF icons to trick users into executing malicious binaries.
MITRE ATT&CK
- Tactic
- Defense Evasion
- Technique
- T1027 Obfuscated Files or Information
- Sub-technique
- T1027.012 LNK Icon Smuggling
- Canonical reference
- https://attack.mitre.org/techniques/T1027/012/
Sumo Detection Query
/* T1027.012 - LNK Icon Smuggling - Sumo Logic CSE / Sysmon */
(_sourceCategory="windows/sysmon" OR _sourceCategory="*WinEventLog*Sysmon*")
| json auto
| where EventID in ("1", "11", "22")
| eval detection_type = ""
/* LNK file creation by scripting engine (EventID 11) */
| where (EventID = "11" AND toLowerCase(TargetFilename) matches "%.lnk"
AND (
Image matches "*\\powershell.exe" OR Image matches "*\\cmd.exe" OR
Image matches "*\\wscript.exe" OR Image matches "*\\cscript.exe" OR
Image matches "*\\mshta.exe" OR Image matches "*\\rundll32.exe" OR
Image matches "*\\regsvr32.exe" OR Image matches "*\\certutil.exe"
))
OR
/* Padded commandline from explorer.exe (EventID 1, Kimsuky) */
(EventID = "1" AND
(Image matches "*\\powershell.exe" OR Image matches "*\\cmd.exe" OR
Image matches "*\\wscript.exe" OR Image matches "*\\mshta.exe") AND
ParentImage matches "*\\explorer.exe" AND
CommandLine matches "* *")
OR
/* Suspicious binary from Temp via explorer.exe (EventID 1, Mustang Panda) */
(EventID = "1" AND ParentImage matches "*\\explorer.exe" AND
(
toLowerCase(Image) matches "*\\office.exe" OR
(toLowerCase(CommandLine) matches "*\\temp\\*.exe" OR toLowerCase(CommandLine) matches "*\\appdata\\local\\temp\\*.exe" OR toLowerCase(CommandLine) matches "*\\appdata\\roaming\\*.exe")
))
OR
/* DNS lookup from explorer.exe for non-standard domains (EventID 22) */
(EventID = "22" AND Image matches "*\\explorer.exe" AND
(
QueryName matches "*.ps1" OR QueryName matches "*.exe" OR QueryName matches "*.dll" OR
!(QueryName matches "*.microsoft.com" OR QueryName matches "*.windows.com" OR QueryName matches "*.windowsupdate.com")
))
| eval detection_type = if(EventID = "11" AND toLowerCase(TargetFilename) matches "%.lnk", "LNK_creation_by_scripting_engine",
if(EventID = "1" AND CommandLine matches "* *", "LNK_padded_commandline_execution",
if(EventID = "1" AND (toLowerCase(Image) matches "*\\office.exe" OR toLowerCase(CommandLine) matches "*\\temp\\*.exe"), "LNK_suspicious_binary_from_temp",
if(EventID = "22", "LNK_icon_field_dns_lookup", "LNK_unknown"))))
| eval risk_score = if(detection_type = "LNK_suspicious_binary_from_temp", 90,
if(detection_type = "LNK_padded_commandline_execution", 85,
if(detection_type = "LNK_icon_field_dns_lookup", 70,
if(detection_type = "LNK_creation_by_scripting_engine", 65, 50))))
| fields _messageTime, Computer, detection_type, risk_score, Image, CommandLine, TargetFilename, QueryName, ParentImage
| sort by risk_score descSumo Logic detection for T1027.012 LNK Icon Smuggling using Sysmon operational logs. Detects four behavioral patterns: LNK creation by scripting engines (Sysmon 11), padded commandline execution via explorer.exe (Sysmon 1, Kimsuky), suspicious binary execution from temp paths (Sysmon 1, Mustang Panda/TONESHELL), and DNS lookups triggered by LNK icon fields (Sysmon 22). Results include risk scoring.
Data Sources
Required Tables
False Positives & Tuning
- Software installation packages that create LNK shortcuts using cmd.exe or PowerShell as part of setup wizards
- Remote management tools (e.g., desktop shortcuts to internal web apps) that cause explorer.exe DNS lookups to internal domains not matching microsoft.com
- Legitimate portable applications stored in AppData\Roaming that contain spaces in their installation paths triggering the padded commandline heuristic
Other platforms for T1027.012
Testing Methodology
Validate this detection against 4 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Create LNK with External Icon URL
Expected signal: Sysmon EventCode 11 (FileCreate) for the .lnk file creation. EventCode 1 (ProcessCreate) showing powershell.exe creating the file via WScript.Shell COM object.
- Test 2LNK with Padded Target Path (Kimsuky Evasion)
Expected signal: Sysmon EventCode 11 for LNK creation by powershell.exe. If executed: EventCode 1 showing cmd.exe spawned from explorer.exe with 260 spaces in CommandLine, then child powershell.exe process.
- Test 3LNK with PDF Icon Spoofing (Mustang Panda/TONESHELL Pattern)
Expected signal: Sysmon EventCode 11 for LNK creation. EventCode 1 for calc.exe (renamed as office.exe) execution from %TEMP% if the LNK is invoked. EventCode 11 for office.exe copy operation.
- Test 4LNK Executed via Script (Automated Execution Pattern)
Expected signal: Sysmon EventCode 11 for LNK creation by powershell.exe. EventCode 1 for cmd.exe spawned from powershell.exe. If icon URL were external: EventCode 22 DNS query and EventCode 3 network connection.
References (7)
- https://attack.mitre.org/techniques/T1027/012
- https://unprotect.it/technique/shortcut-hiding/
- https://www.uperesia.com/booby-trapped-shortcut
- https://www.securonix.com/blog/detecting-kimsuky-lnk-attack-chain/
- https://symantec-enterprise-blogs.security.com/threat-intelligence/shuckworm-ukraine-usb
- https://blog.talosintelligence.com/mustang-panda-plugx-pubload/
- https://www.sophos.com/en-us/threat-center/threat-analyses/mustang-panda-plugx
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