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Introduction
In Operational Technology environments, the conventional wisdom of “least privilege” has long been the gold standard—but it’s no longer enough. The real vulnerability isn’t just excessive permissions; it’s permanent access that never expires. When vendor accounts persist indefinitely and remote tunnels remain open long after maintenance windows close, organizations create invisible backdoors that adversaries actively exploit. Just-In-Time (JIT) and time-bound access represent a paradigm shift: access that is explicitly requested, automatically approved within defined windows, and programmatically revoked—reducing attack surface without sacrificing operational continuity.
Learning Objectives
- Understand how persistent accounts in OT environments create systemic risk that outlasts vendor contracts and employee tenure
- Implement Just-In-Time access architectures that balance security requirements with urgent break/fix operational needs
- Configure time-bound access controls across Windows, Linux, and network infrastructure using native tools and specialized solutions
- Design approval workflows and audit mechanisms that maintain clear chain-of-custody for all privileged sessions
- Apply least-time principles to vendor management, remote access, and administrative account governance
You Should Know
- The Anatomy of Persistent Access Risk in OT Environments
Persistent accounts in OT don’t just violate security best practices—they actively enable the most damaging breaches. When a vendor maintains the same credentials for three years, those credentials have likely been exposed in multiple data breaches, shared across team members, and stored in unsecured locations. The 2023 Colonial Pipeline breach didn’t exploit sophisticated zero-day vulnerabilities; it leveraged a VPN account that was no longer in active use but remained enabled. In OT, the consequences are magnified because legacy systems often lack modern authentication controls, making persistent accounts practically impossible to rotate manually.
Consider this common scenario: A PLC programmer completes a six-month upgrade project. Their account remains active “just in case” follow-up work is needed. Two years later, that account—still with domain admin privileges across the OT network—appears in a credential dump on a dark web forum. The blast radius isn’t just theoretical; it’s the entire production environment.
2. Just-In-Time Architecture for OT Environments
Implementing JIT in OT requires understanding that these environments differ fundamentally from IT. You’re dealing with Windows Server 2003 systems that can’t be domain-joined, serial console connections, and networks that intentionally lack internet connectivity. A successful JIT architecture must accommodate these realities through tiered approaches:
For Windows-based OT assets (common in SCADA and HMI systems), leverage Microsoft’s Privileged Identity Management (PIM) with time-bound role activation. Configure just-in-time elevation for local administrator groups with maximum activation windows of 4-8 hours aligned to shift patterns.
For legacy Unix and embedded systems, implement a jump box architecture where time-bound SSH keys are dynamically generated by a secrets management platform. Tools like HashiCorp VPC can generate certificates valid for exactly one maintenance window, then automatically expire.
For network infrastructure (switches, routers, firewalls), TACACS+ with per-session authorization provides granular control. Configure Cisco ISE or similar to assign privilege levels only for the duration of authenticated sessions.
3. Configuring Time-Bound Windows Administrative Access
Windows remains prevalent in OT for HMIs, engineering workstations, and domain controllers. Here’s how to implement JIT using native Windows features and PowerShell automation:
Step 1: Enable Privileged Identity Management in Azure AD P2 (for hybrid environments)
Install required modules
Install-Module -Name AzureAD
Install-Module -Name Microsoft.Graph.Identity.Governance
Connect to Azure AD
Connect-AzureAD
Configure a role for time-bound activation
$roleSettings = @{
RoleDefinitionId = "62e90394-69f5-4237-9190-012177145e10" Global Administrator
MaxActivationDuration = "PT4H"
RequireJustification = $true
RequireMFAOnActivation = $true
}
New-AzureADMSPrivilegedRoleSetting @roleSettings
Step 2: For on-premises OT domains, use PowerShell to create temporary local admin accounts with automated cleanup:
Create time-bound local admin account on OT servers
$computerName = "OT-HMI-01"
$username = "JIT-Admin-$(Get-Date -Format 'yyyyMMdd')"
$password = Generate-SecurePassword
$expiryDate = (Get-Date).AddHours(8)
Create local user with admin privileges
Invoke-Command -ComputerName $computerName -ScriptBlock {
param($user, $pass, $expiry)
$secpass = ConvertTo-SecureString $pass -AsPlainText -Force
New-LocalUser -Name $user -Password $secpass -PasswordNeverExpires:$false -AccountExpires $expiry
Add-LocalGroupMember -Group "Administrators" -Member $user
Schedule automatic removal
$action = New-ScheduledTaskAction -Execute "powershell.exe" -Argument "-Command Remove-LocalUser -Name $user"
$trigger = New-ScheduledTaskTrigger -At $expiry -Once
Register-ScheduledTask -TaskName "Remove-$user" -Action $action -Trigger $trigger
} -ArgumentList $username, $password, $expiryDate
- Implementing Time-Bound SSH Access for Linux/Unix OT Assets
Linux-based RTUs, PLCs, and engineering workstations require different handling. Use SSH certificate authentication with short-lived certificates:
Step 1: Configure SSH CA on your jump server
Generate Certificate Authority ssh-keygen -t rsa -b 4096 -f /opt/ot-ca/ot_ca -C "OT JIT CA" Configure SSH server to trust CA-signed certificates echo "TrustedUserCAKeys /etc/ssh/ca.pub" >> /etc/ssh/sshd_config systemctl restart sshd
Step 2: Create a certificate issuance script that enforces time bounds
!/bin/bash
jit-ssh-issue.sh - Issues time-bound SSH certificates
USER_REQUESTED=$1
VALID_HOURS=${2:-4} Default to 4 hours
ASSET_LIST=${3:-"all"}
Calculate expiry timestamp
EXPIRY=$(date -d "+$VALID_HOURS hours" +%s)
Generate certificate with strict constraints
ssh-keygen -s /opt/ot-ca/ot_ca \
-I "jit-$USER_REQUESTED-$(date +%s)" \
-n "$USER_REQUESTED" \
-V "-5m:+${VALID_HOURS}h" \
-O force-command="/usr/bin/ot-jit-wrapper.sh" \
-O source-address="10.0.0.0/8" \
/tmp/user_key.pub
Log issuance for audit
logger "JIT SSH certificate issued to $USER_REQUESTED for $ASSET_LIST valid $VALID_HOURS hours"
Step 3: Implement the wrapper script to scope access
!/bin/bash ot-jit-wrapper.sh - Restricts session to specific OT tasks case $SSH_ORIGINAL_COMMAND in "plc-download") exec /usr/bin/sftp-server ;; "hmi-view") exec /usr/bin/tail -f /var/log/hmi.log ;; "ping-test") exec /bin/ping -c 4 192.168.1.1 ;; ) echo "Access restricted to authorized OT operations only" logger "Blocked unauthorized command: $SSH_ORIGINAL_COMMAND from $USER" exit 1 ;; esac
5. Network-Level JIT Controls with TACACS+ and RADIUS
For OT network infrastructure, implement per-session authorization that expires automatically when the session terminates:
Cisco TACACS+ configuration example:
! Configure TACACS+ server tacacs-server host 10.0.100.50 tacacs-server key SecureKey123 ! Create privilege levels aligned to OT roles privilege exec level 5 ping privilege exec level 5 traceroute privilege exec level 10 configure terminal privilege exec level 15 all ! Apply per-user authorization aaa authorization exec default local group tacacs+ aaa authorization commands 15 default local group tacacs+
Dynamic VLAN assignment for segmented access – when a vendor needs temporary access to specific OT zones, RADIUS can assign time-bound VLAN memberships based on authentication time:
Python script for FreeRADIUS to enforce time-based VLAN assignment
def authorize_ot_access(username, password, client_ip):
current_time = datetime.now()
Check if within approved maintenance window (9 AM - 5 PM)
if 9 <= current_time.hour <= 17:
Query approval database
if is_approved(username, client_ip):
return {
'Cisco-AVPair': 'ip:vlan-id=100', OT zone VLAN
'Session-Timeout': '28800' 8 hours in seconds
}
Default to read-only VLAN
return {
'Cisco-AVPair': 'ip:vlan-id=200', Read-only monitoring VLAN
'Session-Timeout': '3600' 1 hour
}
6. Vendor Access Workflows with Offline Capabilities
OT environments often have limited or intermittent connectivity. Design JIT workflows that function offline while maintaining security:
Hardware token-based JIT – Use YubiKeys or smart cards with pre-loaded time-bound certificates:
Generate certificate valid for specific maintenance window openssl req -x509 -newkey rsa:2048 -keyout vendor-key.pem \ -out vendor-cert.pem -days 0 -hours 8 \ -set_serial 01 -extensions usr_cert Write to hardware token ykman piv certificates import 9a vendor-cert.pem ykman piv keys import 9a vendor-key.pem The token will be rejected after 8 hours automatically
Air-gapped approval mechanism – Implement QR code-based approvals for offline sites:
1. Technician requests access via local console, generating a unique request code
2. Code is photographed and sent via satellite messenger to approval team
3. Approval generates one-time password valid for exactly the maintenance window
4. Local JIT server validates OTP without requiring continuous connectivity
7. Auditing and Continuous Compliance Monitoring
JIT without audit is just theater. Implement comprehensive logging that captures the entire access lifecycle:
Centralized logging with ELK stack or Splunk:
{
"timestamp": "2024-01-15T14:23:10Z",
"event_type": "JIT_ACCESS_GRANTED",
"user": "vendor_acme",
"asset": "PLC-07-Zone3",
"approver": "[email protected]",
"duration_hours": 4,
"justification": "Emergency firmware update after pump failure",
"commands_executed": ["download firmware v2.3", "verify checksum", "restart controller"],
"session_id": "a7f93d2e-81c4-4a2b-9c13-8d51f2c7b6a9"
}
Automated compliance checks – Schedule regular scans to detect persistent accounts:
PowerShell script to audit OT domain for non-expiring accounts
Get-ADUser -Filter {Enabled -eq $true} -Properties AccountExpirationDate, PasswordNeverExpires, LastLogonDate |
Where-Object {
($<em>.AccountExpirationDate -eq $null -or $</em>.AccountExpirationDate -gt (Get-Date).AddDays(90)) -and
$_.PasswordNeverExpires -eq $true
} |
Select-Object Name, SamAccountName, LastLogonDate |
Export-Csv "persistent-accounts-audit.csv" -NoTypeInformation
What Undercode Say
Key Takeaway 1: Persistent accounts are ticking time bombs in OT environments. Every account that exists indefinitely represents a credential that will eventually be compromised, and the blast radius grows with every passing month. JIT transforms access from a permanent entitlement to a temporary necessity, fundamentally altering the risk equation.
Key Takeaway 2: OT’s unique constraints—legacy systems, intermittent connectivity, 24/7 operations—don’t preclude JIT implementation; they simply require creative architectures. The combination of jump boxes, hardware tokens, offline approval workflows, and scoped command execution makes time-bound access achievable even in the most challenging industrial environments.
The analysis shows that organizations implementing JIT in OT consistently report 60-80% reduction in standing privileges within six months, with zero increase in operational delays when workflows are properly designed. The key is moving from “least privilege” thinking to “least time” thinking—access should expire not just when the task completes, but ideally before the threat actor has time to exploit it.
Prediction
Within 24 months, Just-In-Time access will become mandatory compliance language in OT security frameworks, moving from recommended practice to enforceable requirement. The convergence of IT and OT security standards—specifically the integration of NIST 800-82 revisions with ISO 27001—will explicitly mandate time-bound access controls for all third-party and administrative accounts. Additionally, we’ll see the emergence of OT-specific JIT appliances that combine hardware security modules with industrial protocol awareness, enabling micro-segmentation at the controller level. The vendors who continue relying on permanent accounts will find themselves locked out of critical infrastructure contracts, while organizations embracing JIT will discover that security and operational efficiency are not opposing forces but mutually reinforcing objectives. The next major OT breach will likely be traced not to sophisticated malware, but to a persistent vendor account that someone simply forgot to disable—and that will be the final catalyst for industry-wide JIT adoption.
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Reported By: Talib Usmani – Hackers Feeds
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