Detect Right-to-Left Override in Microsoft Sentinel
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/
KQL Detection Query
let RTLO_Char = unicode_codepoints_to_string(dynamic([8238]));
DeviceFileEvents
| where Timestamp > ago(24h)
| where FileName contains RTLO_Char or FolderPath contains RTLO_Char
| project Timestamp, DeviceName, AccountName, FileName, FolderPath, ActionType,
InitiatingProcessFileName, InitiatingProcessCommandLine, SHA256
| sort by Timestamp descDetects file creation or modification events where the filename or path contains the Unicode Right-to-Left Override character (U+202E). This character reverses text display direction, allowing adversaries to disguise executable files as documents or images. Uses unicode_codepoints_to_string to search for the non-printing character.
Data Sources
Required Tables
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 that legitimately use Unicode control characters
- PDF or Word documents containing RTL text segments that may appear in file metadata
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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