Microsoft 365 Security Review
Most breaches in a Microsoft estate start with one account and end in the mailbox, the file share or the tenant itself. We review the configuration and then test the path between those three. CREST-certified testers, fixed price from £3,420, scoped in 24 hours.
- Unlimited retesting
- No rescheduling or cancellation fees
- Fixed quote within 24 hours
“I would highly recommend EJN Labs to any organisation seeking reliable, detailed, and well-managed penetration testing services, particularly for government or enterprise-level projects.”
Imran SaghirProject Lead, SquareOne“There wasn’t another company we could find that could deliver what we needed in the timeframe we needed. The client loved it, and we got instant ROI from the engagement.”
Dan WilcocksonCo-Founder, CelloriTenant reviews that stop at the configuration report say what is switched on. They do not say what an attacker reaches from a compromised user, which is the question the board is actually asking. We do both: the benchmark review, then the attack path from a standard account.
A Secure Score is not a test. It is a checklist with good intentions.
The recurring findings are consistent. Conditional access that covers the applications people remembered. Legacy authentication left enabled for one integration. Sharing links that never expire. Application consent that lets any user grant a third party read access to their mail.
Then the detection side. Audit logging that is on but not retained, alert policies that fire into a mailbox nobody reads, and Defender coverage that stops at the licence boundary. We tell you which of your controls would have seen us.
ISO 27001, SOC 2, PCI DSS and Cyber Essentials Plus audits accept manual penetration test evidence. Scan-only evidence is generally insufficient.
MICROSOFT 365 SPECIFICS
What We Actually Test in a Microsoft 365 Tenant
Ten areas that apply because the estate is Microsoft 365, on top of the standard cloud review. Every finding is verified, reproducible and mapped to CIS Microsoft 365 benchmarks, CWE and CVSS 3.1.
Entra ID configuration
Privileged roles and their standing assignment, break glass accounts, and the gap between the documented and actual role model.
Conditional access and MFA
Policy coverage against real applications, exclusions, device and location exceptions, and phishing resistance.
Legacy authentication
Protocols still enabled, the integrations that depend on them, and what they bypass.
Exchange Online
Mail flow rules, automatic forwarding, mailbox delegation, anti-phishing and impersonation protection.
SharePoint and OneDrive
External and anonymous sharing scope, link expiry, site permissions and access to sensitive libraries.
Teams
External federation, guest access, app permission policies and channel level permissions.
Applications and consent
User consent settings, over-privileged registrations, credential expiry and unused service principals.
Data protection
Sensitivity labels, data loss prevention policies, and the paths where they do not apply.
Audit and detection
Unified audit log coverage and retention, alert policies, and whether a compromise would be visible.
Attack path testing
A real path from a standard account towards privilege, tested rather than assumed, within agreed limits.
METHODOLOGY
What a Microsoft 365 finding looks like
Written the way a finding appears in our reports. The example below is reconstructed from publicly documented research, with hosts, paths and identifiers redacted. We do not republish client findings, named or anonymised.
Legacy authentication path bypasses conditional access and multi-factor authentication
- Affected
- The Microsoft 365 tenant for [redacted], where multi-factor authentication was reported to the board as enforced for all users.
- What we found
- Conditional access required a second factor for browser sign-in, but legacy authentication protocols were still enabled and fell outside the policy. Using a credential pair from a public breach set we reached a mailbox through a legacy protocol with no second factor, and created a forwarding rule.
- Why it matters
- Mailbox access and silent mail forwarding for any account with a reused password, despite multi-factor authentication being reported as fully deployed.
- Fix
- Block legacy authentication in conditional access, enable a security baseline, alert on mailbox forwarding rule creation, and audit existing forwarding rules across the tenant before closing the finding.
Reconstructed from public research: the CIS Microsoft 365 Foundations Benchmark and the Microsoft guidance on blocking legacy authentication with conditional access.
Microsoft 365 Penetration Testing: From Scope to Attestation
CREST-aligned methodology built on OWASP Web Security Testing Guide, OWASP ASVS, NIST SP 800-115, and PTES. Each finding maps to all four standards plus your specific compliance regime.
Reconnaissance
Application mapping, technology fingerprinting, content discovery, parameter enumeration, authentication-flow analysis, role-matrix construction.
Vulnerability Assessment
Authenticated and unauthenticated automated scanning across every user role, plus targeted manual checks for known weakness patterns.
Manual Exploitation
Hands-on testing by a CREST-certified pentester. Business-logic exploitation, chained vulnerabilities, privilege escalation, impact validation.
Reporting + Retest
Executive summary, technical report with CVSS scores and reproduction steps, walkthrough call, free retest after remediation, attestation letter.
CREDENTIALS
Verified Accreditations Auditors Accept
Every credential below is independently verifiable. UK procurement teams, FCA supervisors, ISO 27001 / SOC 2 auditors, and cyber insurance underwriters all recognise these standards.
GET YOUR QUOTE
Get a CREST Microsoft 365 assessment pen test quote in 24 hours
A fixed-price quote back in one business day, from a named CREST assessor. No sales pipeline, no chasing.
- CREST and IASME accredited. Testing your auditors and clients already recognise.
- Fast-track testing within 24 hours where required. Free retest of every fix included.
- Live findings via your client portal, not a four-week PDF.
- Fixed price from £3,420 for a small, single-scope engagement, agreed up front. Most engagements run £4,940 and up. No day-rate surprises.
Dan WilcocksonCo-Founder, CelloriUnder NDA Further named references available on a scoping call.
- We reply within one business day with a fixed-price quote from a named CREST assessor.
- You approve the scope and we book a start date, usually within 24 hours.
- Live findings land in your client portal as we test, with a free retest of every fix.
Get your fixed pen test quote in 24 hours
Quote request received
We will reply within one business day with your fixed-price quote from a named CREST assessor.
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or book a 20-min scoping call first
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COMPLIANCE READY
Reports Mapped to Every Framework
Findings are explicitly tagged to the relevant control reference. Your audit team submits the report directly without translation work.
ISO 27001:2022
Annex A.8.8 management of technical vulnerabilities plus A.5.15-5.18 and A.8.2-8.5 access control validation.
SOC 2 Type I & II
CC6 logical access, CC7 system operations, CC8 change management evidence.
PCI DSS
Requirement 11.4 application penetration testing across cardholder data environments, including ecommerce penetration testing for online retail platforms.
FCA SYSC
SYSC 4.1.1R, 6.1.1R, 13 mapped to each finding for FCA-regulated firms.
UK GDPR
Article 32 effectiveness testing, customer-data security controls, ICO-acceptable evidence.
Cyber Essentials Plus
Direct certification through our IASME body status, single-vendor delivery.
PRICING
Transparent Microsoft 365 Penetration Testing Pricing
Pricing depends on the number of tenants, integrations and roles in scope, and the depth of the configuration review. The day count flexes; the included deliverables stay the same across all engagements.
3 to 4 days
Single user role, basic CRUD application, marketing website with auth. Typically 5-day engagement.
Get a fixed quote4 to 6 days
Multi-role SaaS, business application with payment integration. Typically 8-12 day engagement.
Get a fixed quote6 to 8 days
Multi-tenant platform, complex authorisation matrix, integration-heavy applications. 15-20 day engagement.
Get a fixed quotePart of Technologies We Pen Test. These are examples of the stacks we publish pages for, not a complete list. If yours is not here we still test it. Related pages:
BY SECTOR
Microsoft 365 Penetration Testing for Your Sector
Sector-specialist scoping for UK businesses with sector-specific compliance regimes and threat models.
Fintech & FCA-Regulated
FCA SYSC, Open Banking FAPI 1.0, PSD2 SCA, payment-flow scrutiny, KYC/AML testing.
Fintech sector pageSaaS Companies
SOC 2 Type I & II evidence, multi-tenant boundaries, role escalation, customer-tenant isolation.
SaaS sector pageLaw Firms
SRA Cyber Standard, privileged data, conveyancing fraud defence, partner-tier procurement.
Law firm sector pageHealthcare
NHS DTAC, DSP Toolkit v6, UK GDPR Article 32, EHR systems, telehealth platforms.
Healthcare sector pageInsurance
FCA / PRA Operational Resilience, cyber underwriting, claims data, broker portals.
Insurance sector pagePublic Sector
CCS / G-Cloud framework, NCSC-aligned, citizen-facing services, PSN-compliance scrutiny.
Public sector pageWHY EJN LABS
What You Get From Microsoft 365 Penetration Testing
Six concrete differentiators competitors don’t all match.
CREST-Certified Testers, Verifiable
Every test by a CREST-certified pen tester (CRT, CCT APP, CCT INF where applicable). Verify our company status at crest-approved.org.
24-Hour Startup, Where Required
From signed scope to active testing in a single business day for incident response, audit deadlines, or regulator-driven timelines.
Live Findings, Not 4-Week PDFs
Critical issues reported during testing through your client portal. Your team remediates while testing continues.
Audit-Ready Reports
Executive summary plus full technical report with CVSS scores and explicit framework mappings (ISO 27001, SOC 2, PCI DSS, FCA SYSC).
Free Retests, Standard
Verify remediation of every finding before close-out. Letter of attestation for audit submission included. Most competitors charge £1,500-£3,000 per retest.
UK-Based CREST Testers
Every engagement performed by vetted, UK-based CREST-certified testers, matched to your needs, security clearance, and compliance scope.
FAQ
Frequently Asked
Do you need Global Administrator access?
No. A reader role plus one standard test account is enough for the review and the attack path work.
Is this a penetration test or an audit?
Both, deliberately. The configuration review tells you what is set, the testing tells you what is reachable.
Will you send phishing emails to our staff?
Only if you ask for it. That is the phishing assessment, scoped separately and always with your agreement.
Do you cover Intune and device compliance?
The parts that affect conditional access decisions. A full endpoint management review is a separate engagement.
What about Azure, the cloud platform?
That is the Azure cloud security review. Many clients scope both since identity spans the two.
Can you help us fix what you find?
We give you the exact settings to change and retest for free. We do not take over administration of the tenant.
What is included in the price?
Scoping, testing, the executive summary, the technical report, a walkthrough call and free retests until the finding is closed. One scope, one number, no follow-up invoices.
How fast can you start?
Scope to active testing in 24 hours once the scope is agreed, subject to tester availability in your window.
Are your testers CREST certified?
Yes. EJN Labs is a CREST member company and testing is delivered by CREST-qualified testers. The membership is verifiable on the CREST marketplace.
20+ CREST-accredited testing services in one place
Web, mobile, API, cloud, AI, infrastructure, red team. Pick the test that fits your environment.
Get your Microsoft 365 tenant reviewed
Give us a reader role and one test account. You will have a fixed scope and a number within 24 hours.
