CMMC IA.L2-3.5.5: Prevent Identifier Reuse with Replay-Resistant Authentication
Identifier reuse creates a window of vulnerability where attackers can replay captured authentication credentials to gain unauthorized access. IA.L2-3.5.5 requires you to implement replay-resistant authentication mechanisms and enforce a mandatory lockout period before usernames or identifiers can be reused. This control is critical for protecting both privileged and non-privileged accounts across your network.
What this means
This control mandates two key security practices: (1) Deploy replay-resistant authentication mechanisms—such as multi-factor authentication (MFA), time-based one-time passwords (TOTP), or hardware tokens—to prevent attackers from reusing captured credentials in subsequent login attempts. (2) Establish and enforce a defined period during which previously used identifiers cannot be reassigned to new users or accounts. This temporal separation prevents new account owners from inheriting permission histories or cached credentials tied to the old identifier.
How to comply
- 1.Inventory all network access points requiring authentication (VPNs, remote desktop, applications, privileged accounts).
- 2.Select and deploy replay-resistant authentication mechanisms such as multi-factor authentication (MFA), TOTP, or smart cards for both privileged and non-privileged accounts.
- 3.Define and document a minimum identifier reuse lockout period (e.g., 90 days, 1 year) based on your organization's risk profile.
- 4.Configure identity and access management (IAM) systems to automatically prevent identifier reuse during the lockout period.
- 5.Test authentication flows to confirm replay-resistant mechanisms block captured credentials and that identifiers cannot be reused within the lockout window.
- 6.Document identifier reuse policies in your access control procedures and communicate them to administrators.
- 7.Perform quarterly audits of user account creation and termination logs to verify compliance with the reuse lockout period.
Evidence auditors look for
- MFA configuration reports showing multi-factor authentication enabled on all network access points.
- IAM system screenshots demonstrating replay-resistant authentication mechanism deployment.
- Identifier reuse policy documentation specifying the lockout period and approved authentication methods.
- System logs showing failed replay attempts blocked by replay-resistant mechanisms.
- User account lifecycle records confirming no identifiers were reused within the defined lockout period.
- Audit trail reports from privileged account management (PAM) or IAM tools tracking account creation, termination, and identifier status.
Frequently asked questions
When will FAQs be available?
The FAQ for this control is currently being prepared.
GRCWatch automates identifier reuse compliance by enforcing lockout periods in your IAM configuration, logging all account lifecycle events, and generating audit evidence showing that no identifiers were recycled within your policy window—eliminating manual tracking and assessment risk.
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