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Migration

.NET Framework to .NET 8 Migration

Modernize a .NET Framework app to cross-platform .NET 8 by upgrading project files, replacing Windows-only APIs, and validating behavior with tests and production-like data.

Complexity
High

Executive Summary

This migration upgrades a legacy .NET Framework application to modern, cross-platform .NET 8. The work is usually dominated by dependency upgrades, Windows-only API replacements, and web hosting model changes (especially for older ASP.NET).

Migration Profile

| Dimension | Typical value | |---|---| | Complexity | High | | Downtime | None to low (depends on data + deployment) | | Primary risks | Behavioral changes, library gaps, hosting differences | | Success criteria | Builds cleanly, test suite passes, prod-like smoke tests pass |

Strategic Options

  • In-place upgrade (fastest, highest coordination): upgrade the existing solution and cut over.
  • Side-by-side / strangler (lower risk): route a subset of endpoints to the new .NET service while the old app remains live.

Runbook (phased)

Phase 0 — Inventory

  • Identify target runtime (.NET 8), hosting target (Linux containers vs Windows), and unsupported dependencies.
  • Classify components: Web (MVC/Web API/WebForms), background jobs, libraries, COM/Interop, registry/file-system dependencies.

Phase 1 — Build + Package Modernization

  • Convert legacy project format to SDK-style where applicable.
  • Replace packages.config with PackageReference (or plan it during upgrade).
  • Upgrade NuGet dependencies and remove abandoned packages.

Phase 2 — Code + Runtime Changes

  • Replace Windows-only APIs or isolate them behind interfaces.
  • Move configuration from web.config/app.config to appsettings.json and environment variables.
  • If applicable, migrate ASP.NET to ASP.NET Core hosting and middleware.

Phase 3 — Data + Integration

  • Validate connection strings, TLS, auth handlers, and background processing.
  • Run smoke tests against a production-like database snapshot (sanitized).

Phase 4 — Cutover

  • Ship behind a feature flag / percentage rollout.
  • Monitor error rates and performance; keep a rollback path (blue/green or traffic switch).

Keywords

dotnetcsharpbackendmodernizationupgrade
08:53Z[DRIFT]Next.jsNext.js is 2 major versions behind (current: 14.2.35, latest: 16.1.6).
08:54Z[OWASP]A03:2021 – InjectionUnescaped user input rendered into HTML template (src/routes/admin.ts:42)
08:52Z[SCANNER]semgrepscan signature set is up to date
08:48Z[DRIFT]of dependencies are 2+ major versions behind in acme.39% of dependencies are 2+ major versions behind in acme.
08:50Z[OWASP]A02:2021 – Cryptographic FailuresJWT secret is hardcoded — use environment variables (src/auth/jwt.ts:18)
08:45Z[SCANNER]gitleaksscan signature set is up to date
08:43Z[DRIFT]@types/node@types/node is 3 major versions behind (spec: 22.15.29, latest: 25.2.3).
08:46Z[OWASP]A03:2021 – InjectionRegular expression built from user input — potential ReDoS (src/utils/search.ts:67)
08:38Z[SCANNER]trufflehogstatus: unavailable
08:38Z[DRIFT]electronelectron is 3 major versions behind (spec: ^37.6.0, latest: 40.4.1).
08:42Z[OWASP]A03:2021 – InjectiondangerouslySetInnerHTML used with potentially untrusted content (src/components/RichText.tsx:31)
08:33Z[DRIFT]@types/node@types/node is 5 major versions behind (spec: ^20.17.52, latest: 25.2.3).
08:38Z[OWASP]A05:2021 – Security MisconfigurationCookie set without httpOnly or secure flags (src/middleware/session.ts:12)
08:28Z[DRIFT]@types/supertest@types/supertest is 4 major versions behind (spec: ^2.0.16, latest: 6.0.3).
08:34Z[OWASP]A03:2021 – Injectioneval() called with dynamic expression (src/utils/template-engine.ts:88)
08:23Z[DRIFT]VitestVitest is 4 major versions behind (current: 0.34.6, latest: 4.0.18).
08:30Z[OWASP]A01:2021 – Broken Access ControlRedirect URL comes from user-controlled parameter (src/pages/auth/callback.tsx:15)
08:18Z[DRIFT]@types/node@types/node is 5 major versions behind (spec: ^20.8.0, latest: 25.2.3).
08:26Z[OWASP]A03:2021 – InjectionUnsanitised input passed to MongoDB query (src/services/users.ts:34)
08:13Z[DRIFT]vitestvitest is 4 major versions behind (spec: ^0.34.6, latest: 4.0.18).
08:22Z[OWASP]A03:2021 – InjectionChild process spawned with user-controlled arguments (src/utils/pdf-generator.ts:52)
08:08Z[DRIFT]of dependencies are 2+ major versions behind in @acme/api.31% of dependencies are 2+ major versions behind in @acme/api.
08:18Z[OWASP]A05:2021 – Security MisconfigurationExternal link opened without rel="noreferrer" (src/components/ExternalLink.tsx:8)
08:03Z[DRIFT]@types/node@types/node is 5 major versions behind (spec: ^20.11.0, latest: 25.2.3).
08:14Z[OWASP]A02:2021 – Cryptographic FailuresMath.random() used for token generation — use crypto.randomBytes (src/utils/token.ts:6)
07:58Z[DRIFT]of dependencies are 2+ major versions behind in @acme/workflow-engine.52% of dependencies are 2+ major versions behind in @acme/workflow-engine.
08:10Z[OWASP]A05:2021 – Security MisconfigurationExpress app without Helmet security headers middleware (src/server.ts:1)
07:53Z[DRIFT]@types/node@types/node is 5 major versions behind (spec: ^20.19.9, latest: 25.2.3).
07:48Z[DRIFT]@types/node@types/node is 3 major versions behind (spec: ^22.15.29, latest: 25.2.3).
08:53Z[DRIFT]Next.jsNext.js is 2 major versions behind (current: 14.2.35, latest: 16.1.6).
08:54Z[OWASP]A03:2021 – InjectionUnescaped user input rendered into HTML template (src/routes/admin.ts:42)
08:52Z[SCANNER]semgrepscan signature set is up to date
08:48Z[DRIFT]of dependencies are 2+ major versions behind in acme.39% of dependencies are 2+ major versions behind in acme.
08:50Z[OWASP]A02:2021 – Cryptographic FailuresJWT secret is hardcoded — use environment variables (src/auth/jwt.ts:18)
08:45Z[SCANNER]gitleaksscan signature set is up to date
08:43Z[DRIFT]@types/node@types/node is 3 major versions behind (spec: 22.15.29, latest: 25.2.3).
08:46Z[OWASP]A03:2021 – InjectionRegular expression built from user input — potential ReDoS (src/utils/search.ts:67)
08:38Z[SCANNER]trufflehogstatus: unavailable
08:38Z[DRIFT]electronelectron is 3 major versions behind (spec: ^37.6.0, latest: 40.4.1).
08:42Z[OWASP]A03:2021 – InjectiondangerouslySetInnerHTML used with potentially untrusted content (src/components/RichText.tsx:31)
08:33Z[DRIFT]@types/node@types/node is 5 major versions behind (spec: ^20.17.52, latest: 25.2.3).
08:38Z[OWASP]A05:2021 – Security MisconfigurationCookie set without httpOnly or secure flags (src/middleware/session.ts:12)
08:28Z[DRIFT]@types/supertest@types/supertest is 4 major versions behind (spec: ^2.0.16, latest: 6.0.3).
08:34Z[OWASP]A03:2021 – Injectioneval() called with dynamic expression (src/utils/template-engine.ts:88)
08:23Z[DRIFT]VitestVitest is 4 major versions behind (current: 0.34.6, latest: 4.0.18).
08:30Z[OWASP]A01:2021 – Broken Access ControlRedirect URL comes from user-controlled parameter (src/pages/auth/callback.tsx:15)
08:18Z[DRIFT]@types/node@types/node is 5 major versions behind (spec: ^20.8.0, latest: 25.2.3).
08:26Z[OWASP]A03:2021 – InjectionUnsanitised input passed to MongoDB query (src/services/users.ts:34)
08:13Z[DRIFT]vitestvitest is 4 major versions behind (spec: ^0.34.6, latest: 4.0.18).
08:22Z[OWASP]A03:2021 – InjectionChild process spawned with user-controlled arguments (src/utils/pdf-generator.ts:52)
08:08Z[DRIFT]of dependencies are 2+ major versions behind in @acme/api.31% of dependencies are 2+ major versions behind in @acme/api.
08:18Z[OWASP]A05:2021 – Security MisconfigurationExternal link opened without rel="noreferrer" (src/components/ExternalLink.tsx:8)
08:03Z[DRIFT]@types/node@types/node is 5 major versions behind (spec: ^20.11.0, latest: 25.2.3).
08:14Z[OWASP]A02:2021 – Cryptographic FailuresMath.random() used for token generation — use crypto.randomBytes (src/utils/token.ts:6)
07:58Z[DRIFT]of dependencies are 2+ major versions behind in @acme/workflow-engine.52% of dependencies are 2+ major versions behind in @acme/workflow-engine.
08:10Z[OWASP]A05:2021 – Security MisconfigurationExpress app without Helmet security headers middleware (src/server.ts:1)
07:53Z[DRIFT]@types/node@types/node is 5 major versions behind (spec: ^20.19.9, latest: 25.2.3).
07:48Z[DRIFT]@types/node@types/node is 3 major versions behind (spec: ^22.15.29, latest: 25.2.3).