Fix CSRF in C# and ASP.NET Core
===============================

Call AddAntiforgery() and, after UseAuthentication() and UseAuthorization(),
UseAntiforgery(). Bind form posts with [FromForm] so the token is checked,
render it with IAntiforgery.GetAndStoreTokens(), and never add
.DisableAntiforgery() to a cookie-authenticated endpoint. Change state only in
MapPost endpoints; GET endpoints are never checked.

Page: https://softwaresecurity.com/fix/csrf/csharp-aspnetcore/

What is in this archive
-----------------------
csrf/csharp-aspnetcore/   the project: three implementations of the same code and one test suite
  src/Account/impl/VulnerableDefence.cs   (vulnerable)
  src/Account/impl/FixedDefence.cs   (fixed)
  src/Account/impl/WrongDefence.cs   (a plausible fix that still fails)
run-all.mjs   runs the tests in all three modes and checks the results (Node.js only)
LICENSE-CODE.txt

Run it
------
  Tested with .NET 10.0.12 (SDK 10.0.112, ASP.NET Core runtime 10.0.12).
  run-all.mjs needs Node.js 22 or later. Supported versions:
  https://softwaresecurity.com/fix/versions/

  From the csrf/csharp-aspnetcore folder, install the dependencies once (this
  needs network access):

    dotnet restore tests/Account.Tests --locked-mode

  Then run the tests. IMPL chooses the implementation the tests load:

    # every test passes
    IMPL=fixed dotnet test --project tests/Account.Tests --no-restore --results-directory reports --report-xunit-junit --report-xunit-junit-filename junit.xml
    # an exploit test fails
    IMPL=vulnerable dotnet test --project tests/Account.Tests --no-restore --results-directory reports --report-xunit-junit --report-xunit-junit-filename junit.xml
    # a test fails
    IMPL=wrong dotnet test --project tests/Account.Tests --no-restore --results-directory reports --report-xunit-junit --report-xunit-junit-filename junit.xml

  The JUnit report is written to reports/junit.xml. To run all three modes and
  check the results in one step, run the harness from this top folder (it needs
  only Node.js; --install runs the install step first):

    node run-all.mjs --install csrf/csharp-aspnetcore
    node run-all.mjs csrf/csharp-aspnetcore

Verified
--------
  11 October 2026 on macOS 27.0 (Darwin 27.0.0, arm64), with dotnetSdk 10.0.112,
  aspNetCoreRuntime 10.0.12, mvcTesting 10.0.12, xunitV3 4.0.1,
  microsoftTestingPlatform 2.4.0. Versions and results hold for that date: run
  the tests with your own versions before relying on the fix.

Licence
-------
  The code is MIT licensed (LICENSE-CODE.txt). The page text is CC BY 4.0.
