Detect Right-to-Left Override in Sumo Logic CSE
Adversaries may abuse the right-to-left override (RTLO or RLO) character (U+202E) to disguise a string and/or file name to make it appear benign. RTLO is a non-printing Unicode character that causes the text that follows it to be displayed in reverse. For example, a Windows screensaver executable named 'March 25 \u202Excod.scr' will display as 'March 25 rcs.docx'. Adversaries may abuse the RTLO character as a means of tricking a user into executing what they think is a benign file type. Use of the RTLO character has been seen in many targeted intrusion attempts and criminal activity.
MITRE ATT&CK
- Tactic
- Defense Evasion
- Technique
- T1036 Masquerading
- Sub-technique
- T1036.002 Right-to-Left Override
- Canonical reference
- https://attack.mitre.org/techniques/T1036/002/
Sumo Detection Query
(_sourceCategory=*sysmon* OR _sourceCategory=*windows/security* OR _sourceCategory=*winlogbeat*)
| where EventID in ("1", "11", "15", "4688")
| if(isNull(Image), "", Image) as proc_image
| if(isNull(TargetFilename), "", TargetFilename) as target_file
| if(isNull(CommandLine), "", CommandLine) as cmd_line
| if(isNull(NewProcessName), "", NewProcessName) as new_proc
| where proc_image matches "*\u202e*"
OR target_file matches "*\u202e*"
OR cmd_line matches "*\u202e*"
OR new_proc matches "*\u202e*"
| fields _messageTime, Computer, User, EventID, proc_image, target_file, cmd_line, new_proc, Hashes
| sort by _messageTime descDetects the RTLO Unicode character (U+202E) in process image paths, target file names, command lines, and new process names from Sysmon and Windows Security event logs. Identifies filename extension spoofing where malicious executables are disguised as document or image files by reversing the visible portion of their name.
Data Sources
Required Tables
False Positives & Tuning
- Enterprise software installers for RTL language packs (Arabic, Hebrew) that include legitimately named RTL-formatted resource files during installation
- Multilingual content management platforms that store or process documents with bidirectional Unicode metadata inherited from external content providers
- Forensic or detection engineering test environments where RTLO-named sample files are retained for detection validation purposes
Other platforms for T1036.002
Testing Methodology
Validate this detection against 3 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 File with RTLO Character to Disguise Extension
Expected signal: Sysmon Event ID 11: FileCreate with TargetFilename containing the RTLO character (U+202E). The filename in logs will show the raw Unicode character.
- Test 2Create Executable Masquerading as PDF via RTLO
Expected signal: Sysmon Event ID 11: FileCreate with .scr extension disguised via RTLO. The file appears as 'invoice_2026rcs.pdf' in Explorer but is actually a screensaver executable.
- Test 3RTLO in Registry Value (Windows)
Expected signal: Sysmon Event ID 13: RegistryEvent (Value Set) with the RTLO character in the registry value name. Regedit.exe will display the reversed text but reg.exe will show the raw characters.
References (6)
- https://attack.mitre.org/techniques/T1036/002/
- https://resources.infosecinstitute.com/spoof-using-right-to-left-override-rtlo-technique-2/
- https://blog.trendmicro.com/trendlabs-security-intelligence/plead-targeted-attacks-against-taiwanese-government-agencies-2/
- https://securelist.com/zero-day-vulnerability-in-telegram/83800/
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1036.002/T1036.002.md
- https://github.com/SigmaHQ/sigma/tree/master/rules/windows/file_event
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