Sigma rule: RedSun - TieringEngineService.exe Detected as EICAR Test File

Rule

Title

RedSun - TieringEngineService.exe Detected as EICAR Test File

Status

experimental

Level

critical

Author

Swachchhanda Shrawan Poudel (Nextron Systems)

Date

2026-04-17

File

rules-emerging-threats/2026/Exploits/RedSun/win_defender_exploit_redsun_tiering_engine_detected_as_eicar.yml

Commit

ccbb0369507f796db0b0ae6854c8a2be471b9d84

Detects Windows Defender (EventID 1119 - Remediation Action Failed) flagging TieringEngineService.exe
dropped in a characteristic RS-{GUID} temporary directory, or the RedSun.exe process itself being present.
This covers the staging pattern used by RedSun, a Cloud Files API and opportunistic lock (oplock) based
AV bypass/privilege escalation tool.

RedSun works as follows:
1. Registers a Cloud Files sync root and creates a Cloud Files placeholder for TieringEngineService.exe under %TEMP%\RS-{GUID}\
2. The placeholder file carries EICAR test file content (Virus:DOS/EICAR_Test_File) to reliably trigger
a Defender scan and remediation attempt
3. Requests a batch oplock (FSCTL_REQUEST_BATCH_OPLOCK) on the placeholder file
4. When Defender attempts to scan/quarantine the file, the oplock triggers - holding the file open
5. During the oplock break window, RedSun swaps the mount point (junction) to redirect
\\?\C:\Windows\System32 to the attacker-controlled temp path
6. This races the AV/OS into executing the malicious TieringEngineService.exe with elevated privileges

Log source

product

windows

service

windefend

Detection

# EventID 1119: Microsoft Defender Antivirus has encountered an error trying to take action on malware or unwanted software
# Path field from event: file:_C:\Users\<user>\AppData\Local\Temp\<n>\RS-{GUID}\TieringEngineService.exe
# Threat name 'Virus:DOS/EICAR_Test_File' is expected - RedSun uses EICAR content to reliably trigger a Defender scan/remediation
selection_eid:
    EventID: 1119
    SourceName: 'Real-Time Protection'
selection_susp_path:
    Path|endswith: '\TieringEngineService.exe'
    ThreatName|endswith: 'EICAR_Test_File'
selection_susp_process:
    ProcessName|endswith: '\RedSun.exe'
condition: selection_eid and 1 of selection_susp_*

False positives (as the rule lists them)

• Unlikely

Tags

• attack.stealth
• attack.defense-impairment
• attack.t1036.005
• attack.t1685
• attack.privilege-escalation
• attack.t1055
• detection.emerging-threats

MITRE ATT&CK ids this rule names

• T1036.005
• T1055
• T1685

References

• https://github.com/Nightmare-Eclipse/RedSun/blob/7456cc8cf066f5e5fc6cdf7d3272a466ebd6b2f6/RedSun.cpp#L605
• https://deadeclipse666.blogspot.com/2026/04/public-disclosure-response-for-cve-2026.html

Read on 2026-11-03T00:58:21.399Z under licence sigma-drl-1.1@d5f4c36a from https://github.com/SigmaHQ/sigma/blob/ccbb0369507f796db0b0ae6854c8a2be471b9d84/rules-emerging-threats/2026/Exploits/RedSun/win_defender_exploit_redsun_tiering_engine_detected_as_eicar.yml