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Introduction
Remote Desktop Protocol remains one of the most targeted attack vectors in enterprise environments, yet security teams struggle to understand how exposed RDP services actually behave at the protocol level. Traditional vulnerability scanners merely check for patch levels without revealing how systems respond to malformed negotiation traffic, leaving organizations blind to behavioral anomalies that could indicate compromise or misconfiguration. RDPulse, a newly released behavioral scanner, changes this paradigm by providing pre-authentication visibility into RDP service responses, helping teams identify systems that warrant deeper investigation before attackers exploit them.
Learning Objectives
- Understand how behavioral RDP scanning complements traditional vulnerability assessment methodologies
- Learn to deploy and interpret results from RDPulse across segmented enterprise networks
- Master the identification of anomalous RDP responses that may indicate security risks or misconfigurations
- Apply practical Linux and Windows commands to validate RDP service exposure and patch status
You Should Know
1. Understanding RDPulse Architecture and Installation
RDPulse is a Python-based behavioral scanner that interacts with RDP services at the transport layer without attempting authentication or exploitation. It sends carefully crafted negotiation packets—baseline, malformed, and truncated—to observe how target systems respond, revealing implementation quirks that traditional scanners miss.
Installation on Linux (Ubuntu/Debian):
Clone the repository git clone https://github.com/rodrigobash/edc.git cd edc/rdpulse Install dependencies pip3 install -r requirements.txt Typical dependencies include: scapy, impacket, python-nmap Verify installation python3 rdpulse.py --help
Installation on Windows (PowerShell Admin):
Install Python if not present winget install Python.Python.3.11 Clone repository git clone https://github.com/rodrigobash/edc.git cd edc\rdpulse Install requirements pip install -r requirements.txt
What This Does: The tool leverages Scapy for packet crafting and Impacket for RDP protocol structures, enabling it to construct legitimate and intentionally malformed RDP connection requests. The installation process prepares your environment for network reconnaissance without requiring administrative privileges, though scanning remote networks may need appropriate firewall exceptions.
2. Basic RDP Service Discovery with RDPulse
Before behavioral analysis, you must identify which hosts in your target range are actually running RDP services. RDPulse includes discovery modules that perform efficient port scanning specifically tuned for RDP (TCP 3389) with timeout optimization.
Linux Command:
Basic discovery scan across a /24 subnet python3 rdpulse.py --discover 192.168.1.0/24 --threads 50 --timeout 2 Output format: IP:PORT - RDP detected Example output: 192.168.1.10:3389 - RDP DETECTED 192.168.1.15:3389 - RDP DETECTED 192.168.1.254:3389 - RDP DETECTED
Windows Equivalent:
Using PowerShell native test first
$subnet = "192.168.1"
1..254 | ForEach-Object {
$ip = "$subnet.$_"
if (Test-NetConnection $ip -Port 3389 -WarningAction SilentlyContinue).TcpTestSucceeded {
Write-Host "$ip:3389 - RDP DETECTED" -ForegroundColor Green
}
}
Then feed results to RDPulse
Get-Content rdp_hosts.txt | ForEach-Object {
python rdpulse.py --single $_ --output behavioral_results.csv
}
Technical Explanation: The discovery phase uses SYN scans with configurable timeouts to avoid overwhelming networks while maintaining accuracy. Multi-threading significantly accelerates scans across large ranges, making it practical for enterprise environments with thousands of IPs. Results should be saved to a file for subsequent behavioral analysis.
3. Behavioral Response Analysis: Baseline Testing
Once RDP services are identified, RDPulse performs baseline negotiation to establish how each service responds to standard protocol handshakes. This establishes a “fingerprint” of normal behavior against which anomalies are measured.
Command Structure:
Perform baseline analysis on discovered hosts python3 rdpulse.py --analyze rdp_hosts.txt --mode baseline --output baseline_results.csv Example output analysis cat baseline_results.csv | column -t -s, IP Protocol SecurityProtocol SSL CredSSP Version 192.168.1.10 RDP 5.2 NLA Yes Yes 6.1.7601 192.168.1.15 RDP 5.0 RDP No No 5.0.2195 192.168.1.254 RDP 10.6 SSL Yes Yes 10.0.20348
Windows RDP Configuration Verification:
Check local RDP security settings
Get-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Control\Terminal Server\WinStations\RDP-Tcp" |
Select-Object UserAuthentication, SecurityLayer
Query remote systems for RDP configuration (requires admin)
$computers = Get-Content rdp_hosts.txt
foreach ($computer in $computers) {
try {
$session = New-PSSession -ComputerName $computer -ErrorAction Stop
Invoke-Command -Session $session -ScriptBlock {
Get-ItemProperty "HKLM:\SYSTEM\CurrentControlSet\Control\Terminal Server\WinStations\RDP-Tcp"
}
Remove-PSSession $session
} catch {
Write-Host "$computer unreachable or access denied" -ForegroundColor Red
}
}
What This Reveals: Baseline testing exposes critical configuration data including supported security protocols (RDP, SSL, NLA), CredSSP availability, and exact RDP version strings. Discrepancies between expected and actual configurations—such as older systems running without NLA—represent immediate security gaps requiring remediation.
4. Malformed Packet Testing and Anomaly Detection
The core innovation of RDPulse lies in its ability to send malformed and truncated RDP negotiation packets, observing how services react. This technique can reveal buffer handling issues, crash-prone implementations, or potentially compromised systems exhibiting unexpected tolerance.
Advanced Scanning:
Perform malformed packet testing python3 rdpulse.py --targets rdp_hosts.txt --malformed --truncated --output anomalies.csv Interpret results with grep for anomalies grep "ANOMALY" anomalies.csv 192.168.1.45:3389 - ANOMALY - Truncated packet caused infinite wait 192.168.1.67:3389 - ANOMALY - Malformed packet returned 0x80004005 192.168.1.89:3389 - ANOMALY - Service restarted after testing
Linux Network Debugging Tools:
Monitor RDP traffic during testing sudo tcpdump -i eth0 port 3389 -w rdp_test.pcap Analyze packet captures tshark -r rdp_test.pcap -Y "rdp" -T fields -e ip.src -e rdp.negotiation.type Check for services that crashed (using system monitoring) watch -n 1 "netstat -tunap | grep 3389"
Windows Event Log Correlation:
Check for RDP-related crashes after testing
Get-EventLog -LogName System -EntryType Error -Message "TermDD" -Newest 50
Monitor Terminal Services events
Get-WinEvent -FilterHashtable @{LogName="Microsoft-Windows-TerminalServices-LocalSessionManager/Operational"; ID=21,22,25} -MaxEvents 100
Verify service stability
Get-Service TermService | Format-Table Status, StartType -AutoSize
Security Implications: Services that respond unpredictably to malformed input may be vulnerable to denial-of-service attacks or, in worst cases, may indicate successful exploitation where attackers modified service behavior. Systems showing extreme tolerance—accepting obviously invalid packets—should be prioritized for forensic analysis.
5. CVE-2026-21533 Verification and Patch Compliance
Given the recent February 2026 Patch Tuesday addressing CVE-2026-21533, RDPulse includes specific checks to identify systems potentially vulnerable to this elevation of privilege flaw. While the tool doesn’t exploit the vulnerability, it can detect behavioral patterns associated with unpatched systems.
Targeted CVE Testing:
Run CVE-specific behavioral checks python3 rdpulse.py --cve-check CVE-2026-21533 --targets rdp_hosts.txt Output indicating potentially vulnerable systems cat cve_2026_21533_results.txt 192.168.1.23:3389 - SUSPECT - CVE pattern detected 192.168.1.45:3389 - PATCHED - Expected behavior observed 192.168.1.67:3389 - UNKNOWN - Non-standard response
Windows Patch Verification Commands:
Check installed patches remotely
$computers = Get-Content rdp_hosts.txt
$kbNumber = "KB5021556" Example KB for CVE-2026-21533 (replace with actual)
foreach ($computer in $computers) {
try {
$session = New-PSSession -ComputerName $computer -ErrorAction Stop
$hotfix = Invoke-Command -Session $session -ScriptBlock {
Get-HotFix -Id $using:kbNumber -ErrorAction SilentlyContinue
}
if ($hotfix) {
Write-Host "$computer: PATCHED ($($hotfix.InstalledOn))" -ForegroundColor Green
} else {
Write-Host "$computer: MISSING PATCH" -ForegroundColor Red
}
Remove-PSSession $session
} catch {
Write-Host "$computer: Unable to query" -ForegroundColor Yellow
}
}
Linux-Based Remote Check (using winexe or net):
Alternative using net rpc (requires credentials) for ip in $(cat rdp_hosts.txt); do net rpc registry getvalue "HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\HotFix\KB5021556" -S $ip -U domain/user%password done
6. Network Segmentation and Firewall Analysis
RDPulse’s scanning capabilities extend to testing network segmentation effectiveness by analyzing how RDP responses vary when scanned from different network segments. This helps validate firewall rules and network isolation policies.
Multi-Segment Scanning Strategy:
Scan from different network vantage points
python3 rdpulse.py --discover 10.0.0.0/8 --source-ip 192.168.1.100 --output segment_a.txt
python3 rdpulse.py --discover 10.0.0.0/8 --source-ip 172.16.1.50 --output segment_b.txt
Compare results to identify segmentation gaps
diff segment_a.txt segment_b.txt | grep -E "^>|<" | awk '{print $2}' > segmentation_gaps.txt
Firewall Rule Validation:
Test specific firewall rules with crafted packets python3 rdpulse.py --target 192.168.1.100 --custom-packet "rdp_negotiation_malformed.bin" --output fw_test.log Use hping3 for complementary testing hping3 -S -p 3389 -c 5 192.168.1.100 SYN scan hping3 -2 -p 3389 -c 5 192.168.1.100 UDP scan (rare but possible)
Windows Firewall Logging:
Enable firewall logging on critical servers
netsh advfirewall set currentprofile logging filename %systemroot%\system32\LogFiles\Firewall\pfirewall.log
netsh advfirewall set currentprofile logging maxfilesize 4096
netsh advfirewall set currentprofile logging droppedconnections enable
Analyze logs for RDP traffic patterns
Get-Content C:\Windows\System32\LogFiles\Firewall\pfirewall.log |
Where-Object {$_ -match "3389"} |
Select-Object -First 20
7. Remediation Prioritization and Reporting
The final phase involves converting RDPulse findings into actionable remediation priorities. The tool generates risk-scored reports based on behavioral anomalies, patch status, and configuration weaknesses.
Generate Comprehensive Report:
Create HTML/CSV report with remediation recommendations python3 rdpulse.py --report --input all_results.csv --output rdp_security_report.html Extract high-risk systems python3 rdpulse.py --risk-score --threshold 80 --input all_results.csv > critical_hosts.txt
Automated Remediation Scripting:
PowerShell script to apply recommended changes to vulnerable systems
$criticalHosts = Get-Content critical_hosts.txt
foreach ($host in $criticalHosts) {
try {
$session = New-PSSession -ComputerName $host -ErrorAction Stop
Enable NLA if disabled
Invoke-Command -Session $session -ScriptBlock {
Set-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Control\Terminal Server\WinStations\RDP-Tcp" -Name UserAuthentication -Value 1
Set-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Control\Terminal Server\WinStations\RDP-Tcp" -Name SecurityLayer -Value 2
}
Install missing patch
Invoke-Command -Session $session -ScriptBlock {
Start-Process -FilePath "wusa.exe" -ArgumentList "C:\patches\KB5021556.msu /quiet /norestart" -Wait
}
Remove-PSSession $session
Write-Host "$host remediated successfully" -ForegroundColor Green
} catch {
Write-Host "$host remediation failed: $_" -ForegroundColor Red
}
}
Linux-Based Remediation Tracking:
Generate compliance report for auditors echo "RDP Security Assessment - $(date)" > rdp_compliance.txt echo "===================================" >> rdp_compliance.txt while read ip; do echo "Host: $ip" >> rdp_compliance.txt python3 rdpulse.py --quick-check $ip >> rdp_compliance.txt echo "" >> rdp_compliance.txt done < rdp_hosts.txt
What Undercode Say
1. Behavioral analysis reveals what patch management hides – RDPulse demonstrates that traditional vulnerability scanning, focused solely on patch levels, provides incomplete security visibility. Organizations must adopt behavioral scanning to detect compromised systems, misconfigurations, and implementation flaws that patch status alone cannot reveal.
- Pre-authentication reconnaissance is both defensive and offensive – While RDPulse positions itself as a blue-team tool, the techniques it implements mirror exactly what attackers use during reconnaissance. Security teams must understand these methods to build effective detections, implementing network monitoring that alerts on malformed RDP negotiation attempts targeting multiple hosts.
The release of RDPulse coincides with CVE-2026-21533 patching, highlighting a fundamental truth in Windows security: patching without verification is incomplete. Enterprise environments should integrate behavioral RDP scanning into their regular vulnerability management cycles, particularly for sensitive systems like domain controllers, jump boxes, and terminal servers. The tool’s ability to identify systems with unusual protocol tolerance provides early warning indicators that may precede exploitation attempts. Security operations centers should create alerting rules that correlate RDPulse findings with authentication logs, looking for patterns where anomalously-behaving systems subsequently show successful logins. Network segmentation strategies must be validated using multi-vantage-point scanning as demonstrated, ensuring that isolation controls actually function as designed. Ultimately, RDPulse represents a shift toward deeper protocol analysis in security assessment—a trend that will accelerate as attackers increasingly target implementation flaws rather than simple missing patches.
Prediction
Within twelve months, behavioral RDP analysis tools like RDPulse will become standard components of enterprise vulnerability management platforms, with Microsoft likely incorporating similar capabilities into Defender for Identity and advanced threat protection solutions. The rise of AI-powered security tools will enable real-time behavioral baseline analysis across all enterprise protocols, automatically flagging anomalies without manual scanning. However, this same capability will be weaponized by attackers who will develop evasion techniques specifically designed to mimic normal RDP behavior while conducting reconnaissance, leading to an arms race in protocol-level detection and deception. By 2027, RDP protocol analysis will be as commonplace as port scanning is today, fundamentally changing how organizations approach remote access security.
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