Microsoft Entra Threat Hunting: 10 Sign-in Anomalies for UK SOCs
Microsoft Entra Threat Hunting: 10 Sign-in Anomalies for UK SOCs
With the 2024 UK Cyber Security Breaches Survey reporting that 50% of businesses experienced a cyber attack in the last 12 months, the identity layer has become the primary battleground for UK organisations. For SMEs, MSPs, and FCA-regulated firms, protecting the Microsoft 365 tenant is no longer just about compliance; it is about preventing the catastrophic fallout of a credential harvest that could lead to ICO fines or operational paralysis.
At Gridisys, we have observed a marked shift in attack tactics. Threat actors are no longer relying on brute force; they are leveraging session token theft and sophisticated MFA fatigue to bypass traditional security controls. This article provides a technical roadmap for proactive Microsoft Entra threat hunting, specifically tailored to the UK regulatory and threat environment.
The Strategic Importance of Entra ID Sign-in Monitoring
Effective Microsoft Entra security monitoring is the difference between a minor incident and a full-scale data breach involving UK GDPR non-compliance. While automated tools like Identity Protection are useful, they often fail to capture the subtle, "living-off-the-land" techniques used by groups like LockBit or ALPHV.
When we deploy our managed SOC UK capabilities, we move beyond alerts. We engage in proactive hunting within the Sign-in logs, looking for the discrepancies between expected user behaviour and actual authentication patterns.
10 Anomalies Your SOC Should Hunt Daily
1. Unusual User Agent Strings
Attackers often use headless browsers or outdated tools (like older versions of Python requests) that present non-standard User Agent strings. KQL: SigninLogs | where TimeGenerated > ago(24h) | summarize count() by UserAgent, UserPrincipalName
2. Impossible Travel with High-Risk Score
While Microsoft detects this, filtering for "Impossible Travel" where the risk state remains 'At Risk' without remediation shows where your Conditional Access policies might have gaps.
3. MFA Exhaustion Patterns
Look for a series of 'MFA Failure' events followed immediately by an 'MFA Success'. This is the smoking gun of MFA fatigue attacks.
4. Entra Conditional Access Threats: Bypassing Legacy Protocols
Even if you think you have disabled legacy auth, check for sign-in attempts using protocols like SMTP or IMAP. These are often used by threat actors to test perimeter resilience.
5. Sign-ins from Tor Exit Nodes
For FCA-regulated firms, a login from a known Tor IP should be an immediate red flag. We integrate blocklists into our our UK cybersecurity services to ensure these are caught in real-time.
6. Anomalous Token Issuance
Monitor for Service Principal sign-ins that deviate from historical 'AppID' patterns. This is often indicative of an adversary abusing an OAuth grant.
7. Geo-Velocity Discrepancies
Check for users authenticating from two different UK regions or a UK region and a foreign location within an unrealistic timeframe.
8. The 'Browser Switch' Anomaly
Look for users who typically sign in via Edge/Chrome but suddenly authenticate via a generic Linux environment or mobile device.
9. Guest Account Activity
B2B collaboration is common, but guest accounts are often neglected. Hunt for guest accounts that have successfully accessed resources outside their invited scope.
10. Repeated Interrupted Sign-ins
High volumes of interrupted sign-ins followed by a successful login from a new device often indicate a session token theft attempt.
Strengthening Your Stance Against UK-Specific Threats
UK entities face a unique landscape. Regulations such as the FCA PS21/3 require operational resilience, and NCSC guidance emphasizes the importance of secure identity management. Many of our clients engaging in Cyber Essentials support find that hardening Entra ID is their biggest hurdle to certification.
We recommend implementing a 'Zero Trust' approach where identity is the new perimeter. If you are also managing a hybrid environment, ensure you are not neglecting Google Workspace security as threat actors often move laterally between cloud providers.
Key Takeaways for Your Security Team
- Prioritise MFA: Move beyond SMS-based MFA to FIDO2 or Microsoft Authenticator number matching.
- Conditional Access is King: Use device compliance as a requirement for accessing sensitive data.
- Log Everything: Ensure diagnostic settings for Entra ID are piped into a Log Analytics workspace.
- Automation is Essential: Use KQL playbooks to automate the response to common identity anomalies.
- Proactive Hunting: Don't wait for a Microsoft alert; schedule daily 30-minute hunting sprints.
Frequently Asked Questions
How does UK GDPR impact Entra ID logging?
UK GDPR requires that personal data in logs is protected. Ensure your logging policies are set to 'Privacy' mode where possible and that retention periods align with your Data Protection Impact Assessment (DPIA).
Is Entra ID Protection sufficient for FCA compliance?
While robust, Entra ID Protection is a component of a wider strategy. FCA requirements for operational resilience necessitate a more granular approach to identity monitoring and incident response.
Can Gridisys help with SIEM integration?
Yes, our cybersecurity consulting London team specialises in integrating Microsoft 365 logs into Sentinel and other SIEM platforms for holistic visibility.
Why do we see so many failed sign-ins from foreign countries?
This is standard "background noise" for any UK-based entity. The concern is not the volume, but the specific IPs associated with known C2 (Command and Control) infrastructure.
Contact Gridisys Today
Securing your identity infrastructure against modern adversaries is an ongoing battle that requires expert oversight. If your team is struggling to keep pace with evolving threats or you require assistance meeting stringent FCA or NCSC standards, speak with our lead analysts. We invite you to visit our contact page to schedule a consultation regarding your security posture and managed SOC requirements.