Overview
During a recent Microsoft 365 security review, I worked through an investigation that became more than just alert handling. It turned into a useful governance exercise around guest access, external collaboration, and risk acceptance.
The environment supported external collaboration through SharePoint and Microsoft Entra ID. Guest users had limited directory visibility, and SharePoint custom scripting was disabled, which helped reduce certain risks. However, SharePoint was also configured to allow anonymous “Anyone” sharing links.
That configuration made collaboration easier, but it introduced an important visibility trade-off. Anonymous users can access shared content without authenticating, which means their activity does not generate Entra ID sign-in logs.
Why This Matters
From a SOC perspective, authentication-based monitoring, Conditional Access, MFA enforcement, and identity-driven alerting are limited when users are not required to sign in.
The goal was not to immediately recommend the most restrictive configuration. Instead, the focus was to understand the business need, identify the risks, review existing controls, and determine what level of exposure could be accepted and documented.
Areas Reviewed
- Entra ID external collaboration settings
- Guest invitation permissions
- SharePoint external sharing settings
- Default sharing link configuration
- Anonymous sharing vs authenticated guest access
- Impact on auditability, Conditional Access, MFA, and sign-in logging
- Compensating controls such as limited guest directory access, disabled custom scripting, Microsoft 365 audit logging, and MDR monitoring
Technical Controls vs Governance Controls
A major takeaway was the difference between technical controls and governance controls.
Technical controls define what the platform allows. Governance controls define how the organization manages that access. Both are needed.
For guest access, organizations should be clear on who is allowed to invite external users, who owns guest access decisions, when anonymous sharing is acceptable, how accepted risks are documented, how guest access is reviewed periodically, and which activities should trigger investigation or escalation.
Monitoring Considerations
The objective is not to generate alerts for every expected guest activity, but to maintain enough visibility to identify suspicious behavior.
Expected guest access should be treated differently from guest activity that includes unusual locations, suspicious downloads, impossible travel, failed authentication patterns, or other indicators of compromise.
Key Takeaway
This investigation reinforced an important SOC lesson: security is not always about applying the most restrictive setting. Good security requires understanding business requirements, assessing risk, applying appropriate controls, and documenting decisions clearly.
For me, this was a valuable step in thinking beyond alert resolution and toward L2-level analysis: connecting technical configuration, business context, monitoring limitations, and governance into one practical security recommendation.