Fix open redirects in C# and ASP.NET Core
=========================================

Check Url.IsLocalUrl(returnUrl) and redirect with LocalRedirect(returnUrl):
IsLocalUrl accepts "/" or "~/" paths not followed by "/" or "\" and free of
control characters. Follow an absolute URL only when Uri.TryCreate gives
scheme https, an allowlisted host, the default port and no user info;
otherwise LocalRedirect("~/account"). Never trust StartsWith('/').

Page: https://softwaresecurity.com/fix/open-redirect/csharp-aspnetcore/

What is in this archive
-----------------------
open-redirect/csharp-aspnetcore/   the project: three implementations of the same code and one test suite
  src/Login/Impl/VulnerableAccountController.cs   (vulnerable)
  src/Login/Impl/FixedAccountController.cs   (fixed)
  src/Login/Impl/WrongAccountController.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 open-redirect/csharp-aspnetcore folder, install the dependencies once
  (this needs network access):

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

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

    # every test passes
    IMPL=fixed dotnet test --project tests/Login.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/Login.Tests --no-restore --results-directory reports --report-xunit-junit --report-xunit-junit-filename junit.xml
    # a test fails
    IMPL=wrong dotnet test --project tests/Login.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 open-redirect/csharp-aspnetcore
    node run-all.mjs open-redirect/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, semgrep 1.180.0. 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.
