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NoorQureshiNoorQureshi/security-skills/skills/code-review/code-review-dotnet/SKILL.md

code-review-dotnet

Skill27 starsChanged 32 days agoMITView on GitHub

Security review of .NET / C# code — dangerous sinks and ASP.NET pitfalls. Load when reviewing a C#/.NET codebase/PR, on .cs source in scope, or "review this .NET app". Signals: .csproj/.sln, ASP.NET (Core/MVC/WebForms), BinaryFormatter, SqlCommand, Razor Html.Raw, XmlDocument.

2 other projects use a version of this.

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We split this skill into the rules it gives an agent

2 rules. About 0 are common, 0 are distinctive, and 2 are very specific to this project.

  • ≈0

    Common · estimate

    Many files like this have a rule of this kind.

  • ≈0

    Distinctive · estimate

    This author's own choices. Worth a look.

  • 2

    Very specific

    Tied to their project's names, files or tools. Probably skip.

  • Common
  • Distinctive
  • Very specific
  1. Very specific:

    Run security-code-scan/CodeQL.

    line 47
  2. Very specific:

    Check controller [Authorize]/antiforgery coverage and model-binding scope.

    line 49

≈ “Common” is an estimate: at least 1 in 5 of the 350,495 skill files we read have a rule of the same kind, not the same words. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.

Keep what fits and drop the rest. Your version, ready for your agents.
Files
SKILL.md

.NET / C# source review

When it applies

Reviewing C#/.NET source (ASP.NET Core, MVC, or legacy WebForms). The headline risks are unsafe deserialization, string-built SQL, XXE, and Razor's raw-output escape hatch.

Why it works

.NET ships powerful-but-dangerous serializers (BinaryFormatter, Json.NET with TypeNameHandling, LosFormatter/ViewState) that instantiate arbitrary types, and several XML APIs resolve DTDs by default on older frameworks. Reviews find where these meet untrusted input.

Sinks & patterns (grep, then trace to user input)

  • Deserialization: BinaryFormatter, LosFormatter, SoapFormatter, NetDataContractSerializer, JsonConvert with TypeNameHandling != None, Js.NET/fastJSON polymorphic types → RCE gadgets.
  • SQLi: string-concatenated SqlCommand/ExecuteReader/FromSqlRaw(EF Core) vs parameters.
  • Command exec: Process.Start with concatenated arguments / UseShellExecute.
  • XXE: XmlDocument/XmlReader/XmlTextReader without DtdProcessing=Prohibit (legacy default resolves entities); XmlSerializer with a user-controlled type.
  • XSS: Razor @Html.Raw(...), MvcHtmlString, WebForms <%= %> with unencoded input; Response.Write.
  • Other: path traversal via Path.Combine(root, input), LdapConnection filter injection, reflection (Type.GetType/Activator.CreateInstance) on input, insecure ViewState (no MAC).

Framework specifics

  • ASP.NET Core: model binding over-posting/mass assignment (bind whole entity), [AllowAnonymous] on sensitive actions, disabled antiforgery on POST APIs, exposed dev endpoints, open redirect via Redirect(returnUrl) without Url.IsLocalUrl.
  • WebForms: ViewState deserialization (machineKey), event-validation off.

Method

  1. Run security-code-scan/CodeQL; treat as leads.
  2. rg 'BinaryFormatter|TypeNameHandling|FromSqlRaw|Html\.Raw|XmlDocument|Process\.Start' → trace to input.
  3. Check controller [Authorize]/antiforgery coverage and model-binding scope.
  4. Confirm with web-deserialization, web-sqli, web-xxe, web-command-injection.

Gotchas

  • Json.NET is safe by default — the bug is an explicit TypeNameHandling.All/Auto.
  • EF Core parameterises LINQ; FromSqlRaw/ExecuteSqlRaw with interpolation is where SQLi returns.
  • ViewState RCE needs the machineKey (leaked/weak) — note the precondition.

References

OWASP .NET security cheat sheet; ysoserial.net gadget research; Microsoft secure-coding guidance.

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