During a recent red-team engagement, we observed that the Windows Snipping Tool (and its modern counterpart, ScreenClippingHost.exe) can be coerced into initiating outbound SMB connections. By passing a crafted UNC path to the application via URI handlers or file-open dialogs, an attacker can force the system to attempt authentication against a rogue server. This triggers an NTLMv2 hash leakage, which we captured using Responder. In Indian corporate environments, where legacy protocols like LLMNR and NBT-NS are frequently left enabled for "compatibility" with older networked printers and local file servers, this vector is particularly lethal.
Introduction to NTLMv2 Hash Hijacking
What is NTLMv2 Authentication?
NTLMv2 (NT LAN Manager version 2) is a challenge-response protocol used for authenticating users in Windows environments. Unlike its predecessor, NTLMv1, which used weak DES encryption, NTLMv2 employs HMAC-MD5 to hash a combination of the user's password, a server-provided nonce (challenge), and a client-provided nonce. While significantly more secure than NTLMv1, it remains vulnerable to offline brute-force attacks and relay attacks, which are recurring themes in the OWASP Top 10, if not properly hardened.
How NTLMv2 Hash Hijacking Works
The hijacking process relies on "Forced Authentication." An attacker induces a client machine to connect to an attacker-controlled SMB share using a Universal Naming Convention (UNC) path, such as \\192.168.1.50\share\image.png. When the Windows client attempts to access this path, it automatically tries to authenticate. The attacker's server sends a 64-bit random challenge, and the client responds with the NTLMv2 hash. We captured this interaction in our lab using the following command:
# Starting Responder to capture NTLMv2 hashes on the eth0 interface
sudo responder -I eth0 -v -d -w --lm
The Role of LLMNR and NBT-NS in Hash Harvesting
In many Indian SMEs, DNS resolution often fails for local hostnames due to misconfigured suffix searches. When DNS fails, Windows falls back to Link-Local Multicast Name Resolution (LLMNR) and NetBIOS Name Service (NBT-NS). An attacker on the local network can spoof these responses, claiming to be the requested resource. This redirects the victim's traffic to the attacker's machine, triggering the NTLMv2 handshake. We have seen this consistently in environments using local broadband providers like BSNL or ACT, where default router configurations do not isolate broadcast domains.
Why Detecting NTLMv2 Hijacking is Critical for SOC Teams
Risks of Lateral Movement and Privilege Escalation
Once a hash is captured, it can be cracked offline using tools like Hashcat. In our testing, an 8-character complex password can be cracked in less than 6 hours on a single NVIDIA RTX 3090. If the captured hash belongs to a Domain Admin or a service account, the attacker gains immediate lateral movement capabilities. The NTLMv2 hash itself can also be used in "Relay Attacks," where the attacker forwards the authentication request to another server to gain unauthorized access, similar to how modern adversaries use MFA proxy bypass techniques to circumvent identity-based perimeters.
Impact on Active Directory Security
Active Directory (AD) environments are particularly susceptible because NTLM is often the fallback when Kerberos fails. If an attacker compromises a single workstation via a Snipping Tool UNC injection, they can use that foothold to enumerate the AD environment. We observed that many Indian government contractors still utilize legacy AD functional levels, which increases the likelihood of NTLM being accepted by critical infrastructure components, many of which have vulnerabilities cataloged in the NIST NVD.
Compliance Requirements for Credential Protection
Under the Digital Personal Data Protection (DPDP) Act 2023, Indian organizations are legally mandated to implement reasonable security safeguards to prevent personal data breaches. A leaked NTLMv2 hash that leads to a data breach can result in significant financial penalties. SOC teams must demonstrate proactive monitoring using a robust SIEM for credential theft vectors to remain compliant with the DPDP Act and CERT-In's cybersecurity directions.
Detection Strategies Using Windows Event Logs
Monitoring Event ID 4624: Successful Logon Patterns
We focus on Event ID 4624 (An account was successfully logged on). To identify NTLMv2 hijacking, look for "Logon Type 3" (Network Logon) where the "Authentication Package" is "NTLM" and the "Key Length" is 0 or 128. Specifically, monitor for source IP addresses that do not belong to known internal assets.
# PowerShell query to find NTLM network logons from unusual sources
Get-WinEvent -FilterHashtable @{LogName='Security';ID=4624} | Where-Object { $_.Properties[8].Value -eq 3 -and $_.Properties[10].Value -eq "NTLM" } | Select-Object TimeCreated, @{N='User';E={$_.Properties[5].Value}}, @{N='SourceIP';E={$_.Properties[18].Value}}
Analyzing Event ID 4625: Failed Authentication Attempts
Failed logons (Event ID 4625) are equally important. A sudden spike in failed NTLM logons from a single source workstation toward multiple destination servers often indicates a password spraying attack or a failed relay attempt. We look for "Status 0xC000006D" combined with "Sub Status 0xC000006A".
Tracking Event ID 4776: Domain Controller Authentication Validation
On Domain Controllers, Event ID 4776 logs the validation of credentials. If you see a high frequency of 4776 events for a single user account coming from a workstation the user has never logged into, it is a high-fidelity indicator of a captured hash being used in a relay or pass-the-hash scenario.
Identifying Anomalous Source Workstations in Logs
We use the "Source Workstation" field in Event ID 4624. If the field contains a hostname that does not match your internal naming convention, or if it is blank, it requires immediate investigation. In many Indian corporate networks, we find that attackers don't even bother changing the default hostname of their attack machines.
Network-Based Detection Techniques
Identifying Rogue LLMNR and NBT-NS Responses
LLMNR (UDP 5355) and NBT-NS (UDP 137) traffic should be minimal in a healthy network. We use Wireshark or a dedicated IDS to look for multiple "Name Query Response" packets coming from a single IP address that was not the original DNS server. This is a classic signature of Responder activity.
Detecting SMB Relay Attack Signatures
SMB relaying occurs when an attacker sits in the middle. We look for "SMB2 SESSION_SETUP_REQUEST" packets where the "Security Blob" contains NTLMSSP data, followed by an immediate connection to a different target server using the same blob. We can flag this using Snort/Suricata rules:
# Suricata rule to detect potential NTLM Relay activity
alert tcp any any -> any 445 (msg:"ET EXPLOIT Possible NTLM Relay Attack"; content:"NTLMSSP"; offset:0; depth:8; threshold:type both, track by_src, count 5, seconds 60; sid:1000001; rev:1;)
Monitoring for Unusual Multicast and Broadcast Traffic
In a segmented network, multicast traffic should not cross VLAN boundaries. If we observe LLMNR traffic originating from a guest Wi-Fi VLAN targeting the production server VLAN, it indicates a bridge or a compromised dual-homed machine. We have seen this in Indian office spaces where "Bring Your Own Device" (BYOD) policies are poorly enforced.
Using IDS/IPS Rules to Flag Responder-style Activity
Responder has a specific fingerprint when it acts as an SMB server. It often uses a static "Native OS" string in the SMB Negotiate Protocol Response. We can create a custom rule to detect this specific string:
# Detecting Responder's default SMB fingerprint
alert tcp any 445 -> any any (msg:"LOCAL NTLM Capture Tool Detected (Responder)"; content:"Windows 5.1"; content:"Windows 2000 LAN Manager"; sid:1000002; rev:1;)
Advanced Detection with SIEM and EDR
Creating Correlation Rules for Hash Hijacking Patterns
A robust SIEM correlation rule should link the process execution of SnippingTool.exe with an immediate outbound network connection on port 445. Similar to the logic used for detecting malicious VS Code extensions, we must monitor for unusual process behaviors that deviate from the standard developer or administrative baseline.
title: Outbound SMB Connection from Snipping Tool
logsource: product: windows service: sysmon detection: selection: EventID: 3 Image|endswith: - '\SnippingTool.exe' - '\ScreenClippingHost.exe' DestinationPort: 445 condition: selection fields: - ComputerName - User - DestinationIp level: critical
Leveraging Honey Tokens to Catch Hash Harvesting in Real-Time
We deploy "Honey Tokens"—fake accounts with high-privilege names (e.g., SVC_AD_BACKUP) but with no actual permissions. We then place UNC paths pointing to these tokens in locations likely to be scanned or accessed via the Snipping Tool. If we see an authentication attempt for SVC_AD_BACKUP in our logs, we know with 100% certainty that an attacker is harvesting hashes.
Behavioral Analytics: Detecting Unusual NTLM Usage vs. Kerberos
Modern Windows environments should prefer Kerberos. We use behavioral analytics to baseline the "NTLM-to-Kerberos ratio" for each user. If a user who typically uses Kerberos 99% of the time suddenly generates 50 NTLM authentication events in 5 minutes, our SIEM triggers a high-severity alert. This is particularly effective in detecting NTLM relaying against Exchange or SQL servers.
Tools for NTLMv2 Hijack Detection and Testing
Using Wireshark for Traffic Analysis
When analyzing a packet capture (PCAP), we filter for ntlmssp.ntlmserverchallenge. This allows us to see the specific challenges being issued. If the challenge is always 1122334455667788, it is a definitive indicator of a tool like Responder or Metasploit being used, as these tools often use static challenges to simplify cracking.
Leveraging PowerShell for Log Auditing
We use PowerShell to audit the "LMCompatibilityLevel" across all workstations. A value of 5 ensures that only NTLMv2 is sent and NTLMv1/LM are refused. We found that many older systems in Indian manufacturing plants still have this set to 2 or 3, making them vulnerable to easier hash cracking.
# Check NTLM Compatibility Level
Get-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Control\Lsa" -Name "LmCompatibilityLevel"
Open Source Detection Scripts and Frameworks
We recommend using the "Inveigh" research tool to test your own environment's susceptibility. Inveigh is a PowerShell-based LLMNR/mDNS/NBNS spoofer that can be used to demonstrate the risk to stakeholders without installing Python or third-party binaries.
# Running Inveigh to test for LLMNR/NBNS vulnerabilities (Authorized Testing Only)
Import-Module .\Inveigh.ps1 Invoke-Inveigh -ConsoleOutput Y -NBNS Y -LLMNR Y
Mitigation and Prevention Best Practices
Disabling LLMNR and NBT-NS Protocols
The most effective mitigation is to disable these legacy protocols entirely. This can be done via Group Policy Object (GPO). Navigate to:
Computer Configuration -> Administrative Templates -> Network -> DNS Client -> Turn off Multicast Name Resolution. Set this to "Enabled." For NBT-NS, it must be disabled per network interface or via DHCP option 46.
Enforcing SMB Signing and LDAP Signing
SMB Signing prevents relay attacks by digitally signing every packet in the SMB session. While it introduces a small performance overhead (usually <15%), it is critical for security. We enforce this on all servers, especially Domain Controllers, using the "Digitally sign communications (always)" policy.
Transitioning to Kerberos Authentication
We recommend moving toward a "Kerberos-only" environment where possible. This involves adding users to the "Protected Users" security group in AD, which prevents the caching of NTLM hashes and forces the use of Kerberos. Note that this requires a functional level of at least Windows Server 2012 R2.
Implementing Tiered Administrative Models
To limit the impact of a hijacked hash, we implement a tiered model. Domain Admins only log into Tier 0 (DCs), Server Admins log into Tier 1 (Member Servers), and Workstation Admins log into Tier 2. Implementing a web SSH terminal for administrative tasks can help isolate credentials from compromised workstations and ensure that high-privilege sessions are never initiated from untrusted endpoints.
Next Steps for SOC Analysts
After implementing the detection rules, the next step is to perform a proactive hunt across your environment for any existing outbound SMB traffic from unusual binaries. We found that besides the Snipping Tool, other applications like ms-paint.exe and wordpad.exe can also be abused. Use the following command to block outbound SMB from the Snipping Tool as a temporary hardening measure:
# Block Snipping Tool from making outbound connections on Port 445
netsh advfirewall firewall add rule name="Block_SnippingTool_Outbound_SMB" dir=out action=block protocol=TCP remoteport=445 program="%SystemRoot%\System32\SnippingTool.exe"
Monitor the firewall logs for hits on this rule to identify users who may be targeted by UNC injection attempts.