Detect Right-to-Left Override in Splunk
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/
SPL Detection Query
index=wineventlog sourcetype="XmlWinEventLog:Microsoft-Windows-Sysmon/Operational" (EventCode=1 OR EventCode=11 OR EventCode=15)
| eval has_rtlo=if(match(Image, "\xe2\x80\xae") OR match(TargetFilename, "\xe2\x80\xae") OR match(CommandLine, "\xe2\x80\xae"), 1, 0)
| where has_rtlo=1
| table _time, host, User, EventCode, Image, TargetFilename, CommandLine, Hashes
| sort - _timeDetects the presence of the Right-to-Left Override character (U+202E, UTF-8: 0xE2 0x80 0xAE) in process image paths, target filenames, and command lines across Sysmon Events 1 (Process Create), 11 (FileCreate), and 15 (FileCreateStreamHash). The RTLO character is extremely rare in legitimate file operations.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Legitimate documents in right-to-left languages (Arabic, Hebrew, Farsi) that use bidirectional text control characters
- Internationalized file names in multilingual environments
- Some legacy applications that embed Unicode control characters in filenames
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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