Fix JWT validation in C# and ASP.NET Core
=========================================

Configure JwtBearer's TokenValidationParameters with the issuer's signing key
from configuration (or options.Authority), ValidAlgorithms = [RS256],
ValidIssuer, ValidAudience and a ClockSkew of seconds, leaving ValidateIssuer,
ValidateAudience, ValidateLifetime, RequireExpirationTime and
RequireSignedTokens true. Never replace SignatureValidator or set the
Validate* flags to false to silence IDX errors.

Page: https://softwaresecurity.com/fix/jwt-validation/csharp-aspnetcore/

What is in this archive
-----------------------
jwt-validation/csharp-aspnetcore/   the project: three implementations of the same code and one test suite
  src/Accounts/impl/VulnerableTokenValidation.cs   (vulnerable)
  src/Accounts/impl/FixedTokenValidation.cs   (fixed)
  src/Accounts/impl/WrongTokenValidation.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 jwt-validation/csharp-aspnetcore folder, install the dependencies
  once (this needs network access):

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

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

    # every test passes
    IMPL=fixed dotnet test --project tests/Accounts.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/Accounts.Tests --no-restore --results-directory reports --report-xunit-junit --report-xunit-junit-filename junit.xml
    # a test fails
    IMPL=wrong dotnet test --project tests/Accounts.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 jwt-validation/csharp-aspnetcore
    node run-all.mjs jwt-validation/csharp-aspnetcore

Verified
--------
  11 October 2026 on macOS 27.0 (Darwin 27.0.0, arm64), with dotnetSdk 10.0.112,
  aspNetCoreRuntime 10.0.12, jwtBearer 10.0.12, identityModel 8.19.2, 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.
