.NET Penetration Testing for ASP.NET, Blazor and Windows Estates
We test ASP.NET Core, MVC, Web Forms and Blazor applications the way an attacker with a Windows background would: ViewState and serialisers first, then the authorisation attributes, then IIS itself. CREST-certified testers, fixed price from £3,240, 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, CelloriAn automated scan of an ASP.NET application finds the missing headers and the obvious injection. It does not know what ViewState is, whether MAC validation is on, or whether the machine key in the config was copied from a template five years ago. Those are the findings that end up on the front page of the report.
A scanner reads your .NET app as HTML. We read it as .NET.
The same is true of authorisation. In .NET, access control lives in attributes, filters and inheritance rules, so the flaw is usually a controller that forgot its Authorize attribute, an AllowAnonymous that cascades further than the developer thought, or a role check performed in the UI and nowhere else. We test every endpoint against every role, not the ones the navigation shows us.
Then we look at the platform, because a .NET application is rarely alone. IIS, the app pool identity, the service account, the connection strings in web.config and the Windows authentication path are all part of the attack surface, and they are where a contained web bug becomes a domain problem.
ISO 27001, SOC 2, PCI DSS and Cyber Essentials Plus audits accept manual penetration test evidence. Scan-only evidence is generally insufficient.
.NET SPECIFICS
What We Actually Test in a .NET Application
Ten test areas that apply because the application is .NET, on top of the standard application checks. Every finding is verified, reproducible and mapped to OWASP, CWE and CVSS 3.1.
ViewState and machine keys
Whether ViewState is signed and encrypted, whether MAC validation is enabled, and whether the machine key is unique to the environment. A leaked or default key turns a form field into remote code execution.
Unsafe serialisers
BinaryFormatter, LosFormatter, NetDataContractSerializer and JSON.NET with type name handling set wide open. We test the endpoints that accept serialised objects with known gadget chains.
Authorisation attributes
Controllers and actions missing the Authorize attribute, AllowAnonymous inherited further than intended, role checks only in the view, and object identifiers that are not tied to the caller.
Entity Framework and raw SQL
FromSqlRaw with interpolated strings, dynamic LINQ, stored procedures built by concatenation, and sort or filter parameters that reach the database untouched.
Razor and Blazor rendering
Html.Raw, MarkupString in Blazor, and Blazor Server circuits where the authorisation decision is made on the client side of the connection.
Windows authentication and NTLM
Relay paths into the application, delegation settings on the app pool identity, and what the service account can reach once it is borrowed.
IIS configuration
Path normalisation and short file name enumeration, directory browsing, request filtering, and diagnostic handlers such as trace.axd and elmah.axd left reachable.
Secrets and configuration
Connection strings and keys in web.config and appsettings.json, files served from the web root, key material reused between staging and production, and what error pages disclose.
Legacy Web Forms and WCF
Event validation, .asmx and WCF endpoints, SOAP method enumeration, and the old pages nobody removed when the rewrite shipped.
File handling and uploads
Server.MapPath juggling, virtual path traversal, MIME checks that trust the client, and uploads that land in a folder IIS is willing to execute.
METHODOLOGY
What a .NET 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.
Static ASP.NET machine key allows ViewState deserialisation to remote code execution
- Affected
- The web front end of an internet facing Exchange deployment at [redacted], control panel path under /ecp/.
- What we found
- The application used the default, publicly known validation key, so we could sign our own __VIEWSTATE value. A signed payload carrying a serialised object was accepted and deserialised by the server, and our command ran as the application pool identity.
- Why it matters
- Remote code execution on the mail server from an account with no administrative rights, on a host that also held the mailbox database and the service account used by four other systems.
- Fix
- Apply the vendor update, then generate a unique machineKey per server and keep it out of source control. Where ViewState is genuinely needed, enable MAC validation and ViewState encryption, and restrict deserialisation to an allow list of types.
Reconstructed from public research: CVE-2020-0688, Microsoft Exchange validation key remote code execution, CVSS 3.1 base score 8.8 on the NVD record.
.NET 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 .NET application 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 £3,240 for a small, single-scope engagement, agreed up front. Most engagements run £4,870 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
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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 .NET Penetration Testing Pricing
Pricing depends on app complexity, user-role count, business-logic depth, and integration surface. 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
.NET 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 .NET 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 test .NET Framework as well as .NET Core?
Yes. Web Forms and MVC on the old framework, and .NET Core through to the current release. The older the runtime, the more of the test goes into serialisation and ViewState.
Can you test Blazor applications?
Yes, both hosting models. Blazor Server needs particular attention because the component state lives on the server behind a live connection, and authorisation decisions made in the component can be driven from the client.
Do you need the source code?
No. If you have it, a secure code review finds different things and the two combine well.
Will you test the Windows infrastructure behind the app?
Only if it is in scope. Many clients add the internal network test, because the app pool identity is usually the shortest route into the domain.
Our app is behind a WAF. Does that change anything?
It changes the noise, not the findings. We ask for an allowlist so the test measures the application rather than the WAF, and we note separately what the WAF caught.
How long does a .NET test take?
Most single applications are five to ten days of testing depending on roles and integrations. The scope document says exactly how many days before you sign anything.
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 .NET application tested properly
Send us the stack and the roles. You will have a fixed scope and a number within 24 hours.
