58tm1erroreng (by me 1x0F)

Resolving Microsoft Error 58tm1 via Conditional Access Policy

1. Problem

Several users were unable to sign in to Microsoft 365 applications (e.g., Teams, Office). The following error appeared sporadically:

• Error code: 58tm1

• Accompanying messages:

  • TPM issue
  • Token error
  • Sign-in problems in RDS/FSLogix environments

Previous mitigation attempts:

• FSLogix updates
• Token reset
• TPM workarounds
• Profile cleanup

These measures only provided partial or temporary relief.

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2. Root Cause

The issue was caused by inconsistent authentication between legacy MFA mechanisms and modern authentication.

Microsoft Entra ID evaluates sign-ins based on policies and signals. Conditional Access acts as the central policy engine, determining whether access is allowed or blocked based on defined conditions.

Legacy authentication flows can:

• Generate outdated tokens
• Cause conflicts in RDS and FSLogix profiles
• Trigger TPM or PRT-related errors

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3. Final Fix

Activated Policy

Path:

Microsoft Entra Admin Center
→ Entra ID
→ Conditional Access
→ Policies
→ "Block Legacy MFA Authentication"
→ Status: Enabled

Effect of the Policy

• Blocks old MFA and legacy authentication flows

• Enforces modern authentication (MSAL)

• Prevents token inconsistencies

• Stabilizes sign-ins in:

  • RDS environments
  • FSLogix profile setups
  • Devices without a physical TPM

Result: The 58tm1 error is permanently resolved.

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4. Conditional Access Policy Categories (Entra ID)

Conditional Access is based on policies triggered by risk signals and conditions.

The main policy categories include:

Core Categories

1. User Risk Policy

   • Evaluates the likelihood of a compromised user account

2. Sign-in Risk Policy

   • Evaluates the risk level of a specific login attempt

3. MFA Registration Policy

   • Enforces MFA enrollment for users

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5. Key Conditional Access Signals and Conditions

Policies can react to various conditions, such as:

• User or group
• Device type
• Location
• Application
• User or sign-in risk level

These are evaluated as if-then rules:

If user X signs in under condition Y → then apply action Z.

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6. Best-Practice Conditional Access Policies

Typical recommended baseline policies:

• Require MFA for administrators
• Require MFA for all users
• Block legacy authentication
• Allow access only from compliant devices

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7. Conclusion

The 58tm1 error was caused by a conflict with legacy authentication methods.

Permanent solution:

• Enable the policy “Block Legacy MFA Authentication”

Benefits:

• Unified modern authentication
• More stable token handling
• Fewer sign-in errors in RDS/FSLogix environments
• Improved security posture

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