Prevent reuse of identifiers for a defined period
📖 What This Means
This control ensures that user identifiers (like usernames or account IDs) cannot be reused for a specific period of time after they are deleted or deactivated. This prevents potential security risks where an attacker could reuse old identifiers to gain unauthorized access. For example, if an employee leaves the company and their account is deleted, this control ensures that their username cannot be reassigned to a new employee immediately, reducing the risk of confusion or misuse. Another example is in cloud environments where temporary accounts are created and deleted frequently; preventing reuse ensures these accounts cannot be exploited.
🎯 Why It Matters
Reusing identifiers can lead to security vulnerabilities, such as unauthorized access or identity confusion. For instance, if an old identifier is reused, an attacker might exploit it to impersonate a previous user or gain access to sensitive data. A notable example is the 2017 Uber breach, where attackers accessed systems using old credentials that were still active. From the DoD/CMMC perspective, this control is critical for maintaining secure access to Controlled Unclassified Information (CUI). Failure to implement this control can result in data breaches, compliance failures, and reputational damage.
✅ How to Implement
- 1. In AWS, configure IAM policies to prevent reuse of usernames using the 'aws iam update-account-password-policy' command with 'PasswordReusePrevention' set to a defined period.
- 2. In Azure, use Azure AD to enforce password policies that prevent reuse of identifiers via the 'PasswordPolicies' setting in the Azure portal.
- 3. In GCP, configure Identity and Access Management (IAM) policies to restrict identifier reuse using the 'gcloud iam service-accounts' command.
- 4. Set up logging and monitoring in cloud environments to track identifier creation and deletion events.
- 5. Use cloud-native tools like AWS CloudTrail or Azure Monitor to generate alerts for potential identifier reuse attempts.
📋 Evidence Examples
Password Policy Document
Active Directory GPO Configuration Screenshot
Cloud IAM Policy Logs
User Account Audit Report
Training Records
📝 SSP Guidance
Use this guidance when writing the System Security Plan (SSP) narrative for this control.
How to Write the SSP Narrative
For IA.L2-3.5.5 ("Prevent reuse of identifiers for a defined period"), your SSP narrative should specifically describe: (1) the tools and technologies you use to implement this control, (2) the configuration or process that enforces it, (3) who is responsible for maintaining it, and (4) what evidence proves it's working. Describe how users, devices, and processes are identified and authenticated, including your IAM platform, password policies, MFA implementation, certificate management, and service account controls. Be specific -- name your actual products, settings, and responsible personnel.
Example SSP Narratives
"IA.L2-3.5.5 is implemented using cloud-native controls. [Organization] uses [specific cloud service/feature] to prevent reuse of identifiers for a defined period. The configuration is managed through [Azure Policy/AWS Config/Terraform] and monitored via [SIEM tool]. Responsible party: [IT Security Manager]. Evidence: [specific artifact, e.g., 'Azure AD Conditional Access policy screenshot, CloudTrail logs']."
"IA.L2-3.5.5 is implemented through on-premise infrastructure controls. [Organization] uses [Active Directory/Group Policy/specific tool] to prevent reuse of identifiers for a defined period. Configuration is documented in [location] and audited [frequency]. Responsible party: [System Administrator]. Evidence: [specific artifact, e.g., 'Group Policy export, Windows Event logs']."
"IA.L2-3.5.5 is implemented across both cloud and on-premise environments. [Organization] uses [Azure AD Connect/hybrid tool] to ensure consistent enforcement. Cloud resources are managed via [cloud tool] and on-premise systems via [on-prem tool]. Both environments report to [centralized SIEM]. Responsible party: [IT Director]. Evidence: [artifacts from both environments]."
System Boundary Considerations
- • Identify all authentication entry points (local login, VPN, cloud, API)
- • Document the identity provider(s) and authentication flow
- • Specify MFA methods and coverage
- • Ensure this control covers all systems within your defined CUI boundary where prevent reuse of identifiers for a defined period applies
- • Document any systems where this control is not applicable and explain why
Key Documentation to Reference in SSP
- 📄 Identification and Authentication Policy
- 📄 Password policy configuration
- 📄 MFA enrollment records
- 📄 Service account registry
- 📄 Evidence artifacts specific to IA.L2-3.5.5
- 📄 POA&M entry if control is not fully implemented
What the Assessor Looks For
The assessor will test authentication mechanisms, verify MFA is enforced for required access paths, check password policy configuration, and review service account documentation.
💬 Self-Assessment Questions
Use these questions to assess your compliance. Each "NO" answer provides specific remediation guidance.
Question 1: Have you implemented a policy preventing identifier reuse for a defined period?
Question 2: Is the identifier reuse prevention policy enforced across all environments (cloud, on-premise, hybrid)?
Question 3: Are logs maintained to track identifier creation and deletion events?
Question 4: Are regular audits conducted to verify compliance with the identifier reuse prevention policy?
Question 5: Is staff trained on the identifier reuse prevention policy?
⚠️ Common Mistakes (What Auditors Flag)
1. Not defining a specific period for identifier reuse prevention.
2. Inconsistent enforcement across cloud and on-premise environments.
3. Failing to maintain logs of identifier creation and deletion.
4. Not conducting regular audits.
5. Lack of staff training on the policy.
📚 Parent Policy
This practice is governed by the Identification and Authentication Policy