SOAP, gRPC and WebSocket Penetration Testing
Not every API is REST, and the tooling most testers reach for stops at REST. We test the legacy SOAP estate, the gRPC services behind your gateway and the WebSocket channels nobody scopes. CREST-certified testers, fixed price from £2,860, 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, CelloriSOAP services are usually the oldest thing in the estate and the best connected. A WSDL lists every operation, the parsers behind them accept external entities unless someone turned that off, and the authentication is often a header that was never validated properly.
The protocol nobody scopes is the one still running payroll
gRPC brings the opposite problem. It is modern, binary and invisible to most tooling, so services get exposed with reflection enabled and no authentication interceptor on one of the methods, and nobody notices because nothing is readable in a proxy.
WebSockets fail in a third way. The handshake is authenticated, the messages afterwards are not, and a session that loses its rights mid-connection keeps receiving everything it was subscribed to.
ISO 27001, SOC 2, PCI DSS and Cyber Essentials Plus audits accept manual penetration test evidence. Scan-only evidence is generally insufficient.
PROTOCOL SPECIFICS
What We Actually Test in a Non-REST API
Ten test areas that apply because the interface is SOAP, gRPC or WebSocket rather than REST, on top of the standard API checks. Every finding is verified, reproducible and mapped to the OWASP API Top 10, CWE and CVSS 3.1.
Service enumeration
WSDL and schema discovery, gRPC reflection, and the operations that exist but are not documented.
XML parsing
External entities, entity expansion, schema poisoning and server-side request forgery through XML.
SOAP authentication
WS-Security headers, signature and timestamp validation, and replay of captured envelopes.
gRPC interceptors
Authentication and authorisation per method, metadata handling, and methods missing from the interceptor chain.
Message validation
Protobuf and XML validation, unexpected fields, oversized messages and type confusion.
WebSocket authorisation
Authentication at handshake against authorisation per message, and what happens when rights change mid-session.
Object level authorisation
Identifiers in messages accepted without an ownership check, across every operation.
Transport and origin
TLS configuration, certificate verification between services, and origin checks on the WebSocket upgrade.
Rate limiting and resource use
Flooding, long-lived connections, expensive operations and the effect on the service behind them.
Gateway translation
REST to gRPC or SOAP translation layers, header forwarding, and authorisation assumed to have happened upstream.
METHODOLOGY
What a SOAP and API 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.
XML external entity processing on a SOAP endpoint reads server files and reaches internal hosts
- Affected
- A legacy partner integration endpoint at [redacted], SOAP 1.1 over HTTPS, authenticated with a shared secret.
- What we found
- The endpoint parsed XML with external entities enabled. A document type declaration in the request body returned the contents of a local file inside the fault message, and a second entity pointed at the cloud metadata service, which responded with instance credentials.
- Why it matters
- Local file read from the application server and server side request forgery into the internal network, ending at a credentials endpoint that granted access to the storage account.
- Fix
- Disable document type declarations on every parser, use one hardened parser factory across the codebase, and apply an egress policy so the service cannot reach the metadata endpoint at all.
Reconstructed from public research: the OWASP XML External Entity prevention cheat sheet, which records that several widely used Java and .NET XML stacks still ship with entity resolution enabled by default.
API 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 API 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 £2,860 for a small, single-scope engagement, agreed up front. Most engagements run £4,410 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 API 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.
2 to 4 days
Single user role, basic CRUD application, marketing website with auth. Typically 5-day engagement.
Get a fixed quote4 to 5 days
Multi-role SaaS, business application with payment integration. Typically 8-12 day engagement.
Get a fixed quote5 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
API 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 API 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
Can you test without documentation?
Yes. WSDL and gRPC reflection usually give us what we need, and where they do not we work from captured traffic.
Is this separate from your API page?
The API page covers REST. This one covers the protocols that need different tooling. Many engagements include both.
Do you test message queues too?
Broker exposure is covered in the internal infrastructure test. Message contents that cross a trust boundary are in scope here.
What about mutual TLS?
Fully in scope, including whether certificate verification is actually enforced on both sides.
Our SOAP services are internal only.
Then we test them from the position of a compromised neighbouring service, which is how they would be reached.
Do you need a test client?
Helpful but not required. We build our own from the schema.
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 APIs tested, whatever the protocol
Tell us what the interface is and where it runs. You will have a fixed scope and a number within 24 hours.
