Enterprise Cybersecurity Audits: Common Vulnerabilities and How to Address Them

Enterprise cybersecurity audits routinely uncover persistent vulnerabilities resulting from legacy protocol fallback, unsegmented Active Directory trust relationships, and unmonitored service account permissions rather than zero-day software exploits. Remediating these audit findings requires structured technical controls across Kerberos delegation, NTLMv1 disabling, network micro-segmentation, and egress filtering.

Addressing these foundational attack paths eliminates lateral movement vectors and hardens the enterprise against automated credential harvesting.

1. Disabling Legacy Name Resolution Protocols (LLMNR and NBT-NS)

The most consistent penetration testing finding across enterprise networks is the presence of Link-Local Multicast Name Resolution (LLMNR) and NetBIOS Name Service (NBT-NS) broadcasts.

Threat Mechanics

When a Windows client attempts to resolve a non-existent internal hostname or misspelt share name, it falls back to broadcasting LLMNR (UDP 5355) and NBT-NS (UDP 137) across the local subnet. An attacker on the local broadcast domain running tools such as Responder intercepts these queries, spoofs authoritative responses, and forces the victim host to send NTLMv2 password hashes.

Technical Remediation

Disable LLMNR globally via Active Directory Group Policy:

Computer Configuration > Administrative Templates > Network > DNS Client
Setting: Turn off multicast name resolution
Value: Enabled

Disable NetBIOS on all DHCP-enabled interfaces via DHCP Server Option 043 (Vendor Specific Info) or by script across all managed endpoints:

# PowerShell remediation to disable NetBIOS across all network adapters
$adapters = Get-WmiObject -Class Win32_NetworkAdapterConfiguration | Where-Object { $_.IPEnabled -eq $true }
foreach ($adapter in $adapters) {
    $adapter.SetTcpipNetbios(2) # 2 = Disable NetBIOS over TCP/IP
}

2. Eliminating NTLMv1 and Enforcing SMB Signing

Legacy NTLM authentication remains vulnerable to rainbow table precomputation and relay attacks.

Disabling NTLMv1

Configure the Lanman Authentication Level in Group Policy:

Computer Configuration > Windows Settings > Security Settings > Local Policies > Security Options
Setting: Network security: LAN Manager authentication level
Value: Send NTLMv2 response only. Refuse LM & NTLM

Enforcing SMB Message Signing

To neutralize SMB relay attacks, require digital signatures on all Server Message Block (SMB) communications:

Setting: Microsoft network server: Digitally sign communications (always)
Value: Enabled

Setting: Microsoft network client: Digitally sign communications (always)
Value: Enabled

Enforcing SMB signing prevents intermediate attackers from intercepting authenticated NTLM hashes and replaying them to gain administrative access on adjacent servers.

3. Securing Kerberos Delegation and Service Accounts

Unconstrained Kerberos delegation allows compromise of a single web or database server to escalate into complete domain compromise.

Kerberos Delegation Vulnerability

When a service account configured with Unconstrained Delegation authenticates a user, it stores a copy of the user's Ticket Granting Ticket (TGT) in local memory (LSASS). If an attacker compromises the server, they extract the TGT and impersonate the user across any resource in the Active Directory domain.

Remediation Protocol

1. Audit unconstrained delegation across domain accounts using Active Directory PowerShell:

   Get-ADComputer -Filter {(TrustedForDelegation -eq $True)} -Properties TrustedForDelegation
   Get-ADUser -Filter {(TrustedForDelegation -eq $True)} -Properties TrustedForDelegation
   

2. Convert all unconstrained delegation to Resource-Based Constrained Delegation (RBCD).
3. Migrate standard service accounts with static passwords to Group Managed Service Accounts (gMSA), which feature automatic 30-day password rotation and eliminate interactive logon rights:

   New-ADServiceAccount -Name "svc_sql_prod" -DNSHostName "sql01.corp.internal" -PrincipalsAllowedToRetrieveManagedPassword "SQL-Cluster-Hosts"
   

4. Active Directory Administrative Tiering

Audit teams frequently flag "Privilege Creep," where Domain Administrators log into standard user workstations, exposing high-privilege credentials in LSASS memory to pass-the-hash attacks.

Implementing the Three-Tier Model

Enforce strict administrative tiering boundaries:

[Tier 0: Control Plane] ──► Domain Controllers, PKI, Azure AD Connect, PAM
           │ (Strict Isolation: Only Tier 0 Admins, Dedicated Privileged Access Workstations)
           ▼
[Tier 1: Server Plane]   ──► Member Servers, Database Hosts, ERP Systems, Hypervisors
           │ (Tier 1 Admins: Local Admin on servers only; blocked from Tier 0)
           ▼
[Tier 2: Workstation]    ──► End-user laptops, Desktops, Printers, Mobile Devices
             (Tier 2 Admins: Helpdesk staff; completely isolated from T1 and T0 credentials)

Enforce separation using Group Policy User Rights Assignment:

• Prevent Tier 0 administrators from logging on locally or via Remote Desktop to Tier 1 servers and Tier 2 workstations.
• Prevent Tier 1 administrators from logging on to Tier 0 infrastructure.

5. Egress Traffic Filtering and Port Hardening

Many enterprise perimeter firewalls permit unrestricted outbound TCP/UDP traffic from internal servers, allowing malware to establish command-and-control (C2) channels over non-standard ports.

Egress Filtering Policy Baseline

Apply default-deny egress policies across all server subnets, permitting only required protocols:

# Permit approved outbound synchronization only
permit tcp object-group G_NTP_SERVERS any eq 123
permit udp object-group G_DNS_RESOLVERS any eq 53
permit tcp object-group G_INTERNAL_PROXIES any eq 443

# Explicitly deny direct outbound connections from general server VLANs
deny ip any any log-input

Implementing these structured hardening controls systematically resolves core audit findings and establishes defensible enterprise network boundaries.