JavaScript and TypeScript Penetration Testing
Framework-agnostic testing for anything built in JavaScript or TypeScript: the bundle, the DOM, the tokens and the API behind it. CREST-certified testers, fixed price from £2,520, 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, CelloriTypeScript is a development-time guarantee. By the time a request reaches your server the types are gone, so validation has to exist on the server, and the first thing we check is whether it does or whether the interface was trusted to do it.
Types disappear at runtime. The bundle does not.
The bundle is the second area. We pull the production build, recover what we can from source maps, and list the API paths, the administrative routes and the feature flags that the application knows about. That list is the test plan for the API.
Then the browser-side classes that never go away: markup written from user data, tokens kept where any script can read them, third party scripts with the same privileges as your own code, and dependencies with known issues that are actually reachable rather than merely installed.
ISO 27001, SOC 2, PCI DSS and Cyber Essentials Plus audits accept manual penetration test evidence. Scan-only evidence is generally insufficient.
JAVASCRIPT SPECIFICS
What We Actually Test in a JavaScript Application
Ten test areas that apply to any modern JavaScript or TypeScript front end, whatever framework it uses, on top of the standard application checks. Every finding is verified, reproducible and mapped to OWASP, CWE and CVSS 3.1.
Bundle and source maps
Whether map files are published, what the build reveals, and which internal endpoints and flags are visible to anyone.
Client-side authorisation
Routing guards, conditional rendering and disabled controls tested against the API with every role.
DOM injection sinks
Markup written from user data, sanitiser configuration, template helpers and third party widgets.
Token and session storage
Local storage, session storage, cookies and what an injection finding would reach.
Authentication flows
OAuth and OIDC in the browser, redirect handling, PKCE, and social or enterprise login paths.
API contract
Every endpoint the bundle references, tested for object level authorisation, mass assignment and rate limits.
Dependencies
Known issues in the packages that are actually reachable from your code, and how they are reached.
Third party scripts
Analytics, tag managers, chat widgets and payment scripts, and what they can do inside your origin.
Headers and policy
Content security policy that a single page application can live with, clickjacking and cross-origin configuration.
Build and deployment
Environment variables inlined at build time, artefacts left in the web root and what the deployment platform exposes.
METHODOLOGY
What a JavaScript 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.
Cross window message listener accepts messages from any origin
- Affected
- The embedded payment widget rendered on the checkout page at [redacted].
- What we found
- The message event listener parsed incoming data and wrote it into the page, but never checked the sending origin. Any page that framed the widget, or any window opened by the site, could drive it, including changing the payee details shown to the customer.
- Why it matters
- An attacker controlled page could alter what the customer saw immediately before they confirmed a payment, and could read values the widget echoed back into the channel.
- Fix
- Check the event origin against an allow list before touching the data, validate the message shape, and set frame ancestors in the content security policy so only your own origins can embed the widget.
Reconstructed from public research: the MDN guidance on verifying origin in window.postMessage handlers and the OWASP DOM based cross-site scripting prevention cheat sheet.
JavaScript 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 JavaScript 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 £2,520 for a small, single-scope engagement, agreed up front. Most engagements run £3,760 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.
Your data stays with us. No newsletter signup.
or book a 20-min scoping call first
We reply within one business day. Your data stays with us. No newsletter signup.
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 JavaScript 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 3 days
Single user role, basic CRUD application, marketing website with auth. Typically 5-day engagement.
Get a fixed quote3 to 5 days
Multi-role SaaS, business application with payment integration. Typically 8-12 day engagement.
Get a fixed quote5 to 7 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
JavaScript 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 JavaScript 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
Which frameworks does this cover?
Any of them, and none. If you are on React, Angular, Vue or Next.js the dedicated page is a better fit. This page is for everything else, including hand-rolled and mixed front ends.
Does TypeScript make the application safer?
It removes a class of bugs during development. It removes nothing at runtime, which is where we test.
Do you need the repository?
No. We work from the deployed build and any published source maps.
Is the API included?
Yes. Most findings are there, so it is in scope by default.
Can you test a component library?
Only as part of an application. On its own there is no authorisation boundary.
What about Node on the server?
That is the Node.js page. If you run both ends we scope them together.
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 JavaScript application tested properly
Send us the application and the roles. You will have a fixed scope and a number within 24 hours.
