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Introduction:
In the modern interconnected enterprise, security teams have spent millions fortifying their own perimeters, only to realize that the drawbridge was left down for a contractor. The concept of the “extended enterprise” means your security posture is now literally defined by the hygiene of your partners. When vendor access is left open—via stale accounts, missing MFA, or excessive permissions—attackers bypass your defenses entirely, exploiting the implicit trust granted to third parties to exfiltrate customer databases and supply chain data.
Learning Objectives:
- Objective 1: Identify and audit dormant vendor accounts and excessive permissions across identity providers.
- Objective 2: Implement technical controls (MFA, Just-In-Time access) to enforce zero-trust for third parties.
- Objective 3: Utilize log analysis and automation to detect anomalous behavior originating from partner integrations.
You Should Know:
- Auditing the Ghosts in the Machine: Finding Stale Vendor Accounts
The primary vector highlighted in the post is “Vendor accounts never deactivated.” These orphaned accounts often persist long after a contract ends, providing a stealthy entry point.
Step‑by‑step guide: Auditing Dormant Accounts in Microsoft Entra ID (Azure AD)
Most organizations use Entra ID (formerly Azure AD) for B2B collaboration. To find guest accounts that haven’t been used recently, you can use the Microsoft Graph PowerShell SDK.
1. Install the module: `Install-Module Microsoft.Graph -Scope CurrentUser`
2. Connect and consent: `Connect-MgGraph -Scopes “User.Read.All”, “AuditLog.Read.All”`
- Run a query to find guest accounts inactive for 90 days:
Calculate the date 90 days ago $inactiveDate = (Get-Date).AddDays(-90).ToString("yyyy-MM-ddTHH:mm:ssZ") Retrieve guest users whose last sign-in is null or before the inactive date Get-MgUser -Filter "userType eq 'Guest'" -Property "Id,DisplayName,UserPrincipalName,CreatedDateTime,SignInActivity" | Where-Object { $<em>.SignInActivity -eq $null -or $</em>.SignInActivity.LastSignInDateTime -lt $inactiveDate } | Format-Table DisplayName, UserPrincipalName, CreatedDateTimeWhat this does: It filters for guest users (vendors) and checks their
SignInActivity. If they haven’t signed in for 90 days, they are prime candidates for removal or review. -
Killing Shared Credentials: Implementing MFA and Conditional Access
The post mentions “Shared credentials between teams.” This is often a symptom of a missing identity management strategy. Enforcing MFA is the baseline, but forcing it specifically for vendors requires Conditional Access policies.
Step‑by‑step guide: Enforcing MFA for External Users (Azure AD)
1. Navigate to Azure Active Directory > Security > Conditional Access.
2. Click + New policy.
- Assignments > Users and groups: Select “Select users and groups,” then check “All guest and external users.”
- Cloud apps or actions: Select “All cloud apps” (to ensure no vendor portal is missed).
- Conditions > Sign-in risk (Optional): Set to “High” to trigger MFA only if the login looks anomalous, reducing friction while maintaining security.
- Access controls > Grant: Check “Require multi-factor authentication.”
- Enable policy: Set to “Report-only” initially to monitor impact, then “On.”
3. Automating Least Privilege with Just-In-Time (JIT) Access
The concept of “temporary” permissions becoming permanent is a critical failure. Instead of assigning permanent roles, use a Privileged Identity Management (PIM) solution to require vendors to request elevation.
Step‑by‑step guide: Configuring JIT for a Vendor Role (Azure AD PIM)
1. In Azure AD, go to Identity Governance > Privileged Identity Management (PIM).
2. Select Groups and choose a group that contains vendor accounts (or a role they use).
3. Go to Settings and edit the role/assignment settings.
4. Under Activation, set a maximum duration (e.g., 4 hours). Enable “Require approval” to activate.
5. Under Assignment, set Allow permanent eligible assignment to false. Set Expire eligible assignments after (e.g., 30 days).
6. Command-line equivalent (Microsoft Graph): You can automate membership reviews using the Graph API.
Example: Remove a user from a privileged role after a set time
Requires MS Graph session
$params = @{
principalId = "USER_OBJECT_ID"
roleDefinitionId = "ROLE_ID"
directoryScopeId = "/"
action = "Deactivate"
justification = "Vendor contract ended"
}
New-MgRoleManagementDirectoryRoleAssignmentScheduleRequest -BodyParameter $params
4. Continuous Monitoring: Detecting Anomalous Partner Activity
Attackers leverage the fact that “Monitoring is usually weaker” for partners. You must ingest partner activity logs into your SIEM and baseline their behavior. A partner logging in from a non-standard geo or at odd hours could indicate a breach.
Step‑by‑step guide: Hunting for Anomalies with KQL (Kusto Query Language)
If you use Microsoft Sentinel or Azure Log Analytics, you can query sign-in logs specifically for external users.
1. Go to your Log Analytics workspace.
- Run the following KQL query to find failed sign-ins followed by success, a common brute-force pattern against vendor accounts:
SigninLogs | where UserType == "Member" or UserType == "Guest" // Focus on external members | where ResultType != "0" // Look for failures | summarize FailureCount = count(), FirstFailure = min(TimeGenerated), LastFailure = max(TimeGenerated) by UserPrincipalName, IPAddress | where FailureCount > 10 | join kind=inner ( SigninLogs | where ResultType == "0" // Successful logins | project UserPrincipalName, SuccessTime = TimeGenerated, SuccessIP = IPAddress ) on UserPrincipalName | where SuccessTime between (LastFailure .. (LastFailure + 30m)) // Success within 30 minutes of last failure | project UserPrincipalName, FailureCount, LastFailure, SuccessTime, IPAddress, SuccessIP
What this does: It detects guest accounts that failed to log in many times and then succeeded shortly after—a classic sign of a compromised credential.
5. Securing the API Connection: Vendor Integrations
Vendor access isn’t just about human logins; it’s about API keys and service accounts. If a vendor has an API key to your system that never expires, it’s a permanent backdoor.
Step‑by‑step guide: Rotating and Scoping API Keys
- Identify keys: Use a script to list all service principals and their credentials.
Get-MgServicePrincipal -All | ForEach-Object { $sp = $_ Get-MgServicePrincipalPasswordCredential -ServicePrincipalId $sp.Id } - Apply scoping: Ensure keys are scoped to specific applications, not “full access.” In cloud environments (AWS/Azure), never give a vendor key `Contributor` or `Owner` rights. Instead, create a custom role with explicit permissions.
Example AWS IAM Policy limiting to specific S3 bucket read:{ "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Action": ["s3:GetObject"], "Resource": ["arn:aws:s3:::vendor-specific-bucket/"] } ] }
6. The Linux/Server Angle: SSH Keys for Contractors
In many on-premise or hybrid setups, vendors require SSH access to Linux servers. Leftover `.ssh/authorized_keys` entries are a nightmare.
Step‑by‑step guide: Auditing SSH Keys
Run this script on your jump boxes or critical servers to find keys that haven’t been used recently.
!/bin/bash
Audit SSH authorized_keys for last usage
AUTH_KEYS_FILE="/home/USERNAME/.ssh/authorized_keys"
while IFS= read -r line; do
Skip comments and empty lines
[[ "$line" =~ ^.$ ]] && continue
[[ -z "$line" ]] && continue
Extract the key comment (usually the user/email at the end)
KEY_COMMENT=$(echo "$line" | awk '{print $NF}')
Log the key and check last login of the user
echo "Checking key: $KEY_COMMENT"
lastlog -u USERNAME
echo ""
done < "$AUTH_KEYS_FILE"
Recommendation: Use a configuration management tool (Ansible, Puppet) to centrally manage authorized_keys. If a vendor is offboarded, remove their key from the playbook and redeploy, ensuring it’s wiped from all servers.
What Undercode Say:
The LinkedIn post correctly identifies a catastrophic failure mode in modern security: the erosion of the perimeter due to implicit trust. The key takeaway is that “trust” must be converted into verifiable, short-lived credentials. By implementing Just-In-Time access and rigorous logging, we transform vendor connections from permanent tunnels into audited, temporary bridges. Organizations often fear that enforcing these controls will hinder business velocity, but the opposite is true—a clean, automated vendor onboarding/offboarding process increases agility while drastically reducing risk.
Key Takeaway 1: Treat every vendor connection as a potential breach. Assume the vendor’s own network is compromised and architect your access controls (MFA, short TTLs) accordingly.
Key Takeaway 2: Visibility is control. You cannot secure what you cannot see. Implement continuous auditing of all external identities and their activity logs, using automated alerts for baseline deviations.
Prediction:
Within the next 18 months, we will see regulatory bodies (like SEC and GDPR enforcers) begin to explicitly mandate Third-Party Access Reviews as part of standard compliance audits. The era of “the vendor said they are secure” will end, replaced by requirements for continuous control monitoring (CCM) where enterprises must provide cryptographic proof (via logs and attestations) that partner access is locked down. This will drive massive adoption of Identity Governance Administration (IGA) tools specifically tailored for the external workforce.
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IT/Security Reporter URL:
Reported By: Sam Sabiri – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
