# Block legacy authentication policy is configured
Legacy authentication protocols such as basic authentication for SMTP and IMAP don't support modern security features like multifactor authentication…
Source: https://maester.dev/docs/tests/ZTA.21796
:::note[Maester checks this too]
[CISA.MS.AAD.1.1](/docs/tests/CISA.MS.AAD.1.1) (Legacy authentication SHALL be blocked.), [CIS.M365.5.2.2.3](/docs/tests/CIS.M365.5.2.2.3) (Enable Conditional Access policies to block legacy authentication) check the same setting. Running both reports it twice.
:::
## Overview
Legacy authentication protocols such as basic authentication for SMTP and IMAP don't support modern security features like multifactor authentication (MFA), which is crucial for protecting against unauthorized access. This lack of protection makes accounts using these protocols vulnerable to password-based attacks, and provides attackers with a means to gain initial access using stolen or guessed credentials.
When an attacker successfully gains unauthorized access to credentials, they can use them to access linked services, using the weak authentication method as an entry point. Attackers who gain access through legacy authentication might make changes to Microsoft Exchange, such as configuring mail forwarding rules or changing other settings, allowing them to maintain continued access to sensitive communications.
Legacy authentication also provides attackers with a consistent method to reenter a system using compromised credentials without triggering security alerts or requiring reauthentication.
From there, attackers can use legacy protocols to access other systems that are accessible via the compromised account, facilitating lateral movement. Attackers using legacy protocols can blend in with legitimate user activities, making it difficult for security teams to distinguish between normal usage and malicious behavior.
## Remediation
- [Deploy a Conditional Access policy to Block legacy authentication](https://learn.microsoft.com/entra/identity/conditional-access/policy-block-legacy-authentication?wt.mc_id=zerotrustrecommendations_automation_content_cnl_csasci)
## Run it
The check runs as part of the whole assessment, with the ZeroTrustAssessment module installed:
```powershell
Install-Module ZeroTrustAssessment -Scope CurrentUser
Connect-Maester
Invoke-Maester -Pack ZTA -SkipBuiltIn
```
Leave out `-SkipBuiltIn` to run Maester's own checks in the same run.
About this check
| | |
| --- | --- |
| Severity | Medium |
| Effort to fix | Low |
| Impact on users | High |
| Pillar | Identity |
| Category | Access control |
| Product | [Entra ID](/docs/tests/products/entra) |
| Feature | Conditional Access |
| Area | Authentication |
| ATT&CK | [T1110.003](/docs/tests?mitre=T1110.003) Password Spraying, [T1078.004](/docs/tests?mitre=T1078.004) Cloud Accounts |
| Licence | P1 |
| Tenant | Workforce |
Product, feature, area and ATT&CK are Maester's: the assessment does not record them, so Maester keeps them in the pack's `taxonomy.json`.