Fix mass assignment (over-posting) in C# and ASP.NET Core
=========================================================

Bind the body to an input model record that declares only the fields users may
edit (here ProfileUpdate(DisplayName, Bio)), never to the entity, and copy
those fields onto the entity yourself. System.Text.Json skips undeclared
properties. ASP.NET Core matches JSON names case-insensitively, so a blocklist
that compares exact names misses Role.

Page: https://softwaresecurity.com/fix/mass-assignment/csharp-aspnetcore/

What is in this archive
-----------------------
mass-assignment/csharp-aspnetcore/   the project: three implementations of the same code and one test suite
  src/Profile/impl/VulnerableProfile.cs   (vulnerable)
  src/Profile/impl/FixedProfile.cs   (fixed)
  src/Profile/impl/WrongProfile.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). run-all.mjs needs Node.js 22 or
  later. Supported versions: https://softwaresecurity.com/fix/versions/

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

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

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

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