Detect Right-to-Left Override in Google Chronicle
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/
YARA-L Detection Query
rule t1036_002_rtlo_override {
meta:
author = "Argus Detection Engineering"
description = "Detects Right-to-Left Override (RTLO) character U+202E in process and file events to identify filename extension spoofing"
mitre_attack_tactic = "Defense Evasion"
mitre_attack_technique = "T1036.002"
severity = "HIGH"
confidence = "HIGH"
reference = "https://attack.mitre.org/techniques/T1036/002/"
events:
(
$e.metadata.event_type = "PROCESS_LAUNCH" or
$e.metadata.event_type = "FILE_CREATION" or
$e.metadata.event_type = "FILE_MODIFICATION"
)
(
re.regex($e.principal.process.file.full_path, `\x{202e}`) or
re.regex($e.target.file.full_path, `\x{202e}`) or
re.regex($e.target.file.names[0], `\x{202e}`) or
re.regex($e.principal.process.command_line, `\x{202e}`)
)
condition:
$e
}YARA-L 2.0 rule detecting the RTLO character (U+202E) in UDM process file paths, target file paths, file names, and command lines. Applies regex matching across PROCESS_LAUNCH and FILE_CREATION/MODIFICATION event types ingested from endpoint sensors, covering both execution and file-drop phases of RTLO abuse.
Data Sources
Required Tables
False Positives & Tuning
- RTL language support runtime files deployed to enterprise endpoints during localization rollouts in organizations operating in Arabic- or Hebrew-speaking markets
- Unicode-aware development environments or build pipelines that generate intermediate artifacts with bidirectional text markers as part of internationalization testing
- Authorized DFIR toolkits or threat hunting platforms that stage RTLO test files on endpoints during validation of detection logic
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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