Fix CSV formula injection in C# and ASP.NET Core
================================================

Spreadsheets run a cell that starts with =, +, -, @, tab or carriage return.
CsvHelper's InjectionOptions defaults to None, which quotes but does not
neutralize, so set InjectionOptions.Escape: it prefixes such a cell with a
single quote and still quotes for RFC 4180. Quoting alone does not stop
formula execution.

Page: https://softwaresecurity.com/fix/csv-formula-injection/csharp-aspnetcore/

What is in this archive
-----------------------
csv-formula-injection/csharp-aspnetcore/   the project: three implementations of the same code and one test suite
  src/Contacts/impl/VulnerableContactExporter.cs   (vulnerable)
  src/Contacts/impl/FixedContactExporter.cs   (fixed)
  src/Contacts/impl/WrongContactExporter.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 ASP.NET Core 10 minimal API on .NET 10.0.12. run-all.mjs needs
  Node.js 22 or later. Supported versions:
  https://softwaresecurity.com/fix/versions/

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

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

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

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

Verified
--------
  11 October 2026 on macOS 27.0 (Darwin 27.0.0, arm64), with dotnetSdk 10.0.112,
  aspNetCoreRuntime 10.0.12, csvHelper 33.1.0, xunitV3 4.0.2. 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.
