Modify rule S2083[C#]: Educational content (APPSEC-49) (#1121)

docs/allowed_framework_names.adoc

@@ -1,11 +1,13 @@
 // C#
 * ASP.NET
 * Razor
+* .NET
 // Java
 * JSP
 * Servlet
 * Spring
 * Thymeleaf
+* Java SE
 // JS
 * Express.js
 // PHP

rules/S2083/common/fix/code-rationale.adoc

@@ -0,0 +1 @@
+The following code is vulnerable to path injection as it is constructing a path using untrusted data. This path is then used to delete a file without being validated first. Therefore, it can be leveraged by an attacker to delete arbitrary files.

rules/S2083/common/fix/how-does-this-work.adoc

@@ -0,0 +1,6 @@
+The universal way to prevent path injection is to validate paths constructed from untrusted data. 
+
+The validation should be done as follow:
+
+1. Resolve the canonical path of the file by using methods like `{canonicalization_function}`. This will resolve relative path or path components like `../` and removes any ambiguity regarding the file's location. 
+2. Check that the canonical path is within the directory where the file should be located.

rules/S2083/csharp/how-to-fix-it/dotnet.adoc

@@ -0,0 +1,47 @@
+=== How to fix it in .NET
+
+:canonicalization_function: System.IO.Path.GetFullPath
+include::../../common/fix/code-rationale.adoc[]
+
+[cols="a"]
+|===
+h| Non-compliant code example
+|
+[source,csharp]
+----
+public class ExampleController : Controller
+{
+    private static string TargetDirectory;
+
+    public void Example(string filename)
+    {
+        string path = Path.Combine(TargetDirectory, filename);
+        System.IO.File.Delete(path); // Noncompliant
+    }
+}
+----
+h| Compliant solution
+|
+[source,csharp]
+----
+public class ExampleController : Controller
+{
+    private static string TargetDirectory;
+
+    public void Example(string filename)
+    {
+        string path = Path.Combine(TargetDirectory, filename);
+        string canonicalDestinationPath = Path.GetFullPath(path);
+
+        if (canonicalDestinationPath.StartsWith(TargetDirectory, StringComparison.Ordinal))
+        {
+            System.IO.File.Delete(canonicalDestinationPath);
+        }
+    }
+}
+----
+|===
+
+=== How does this work?
+
+include::../../common/fix/how-does-this-work.adoc[]

rules/S2083/csharp/rule.adoc

@@ -6,6 +6,8 @@ include::../impact.adoc[]
 
 == How to fix it?
 
+include::how-to-fix-it/dotnet.adoc[]
+
 == Resources
 
 include::../common/resources/standards.adoc[]

rules/S2083/java/how-to-fix-it/java-se.adoc

@@ -1,6 +1,7 @@
 === How to fix it in Java SE
 
-The following code is vulnerable to path injection as it is constructing a path using untrusted data. This path is then used to delete a file without being validated first. Therefore, it can be leveraged by an attacker to delete arbitrary files.
+:canonicalization_function: java.io.File.getCanonicalPath
+include::../../common/fix/code-rationale.adoc[]
 
 [cols="a"]
 |===
@@ -48,9 +49,4 @@ public class ApiController
 
 === How does this work?
 
-The universal way to prevent path injection is to validate paths constructed from untrusted data. 
+include::../../common/fix/how-does-this-work.adoc[]
-
-The validation should be done as follow:
-
-1. Resolve the canonical path of the file by using methods like java.io.File/getCanonicalPath. This will resolve relative path or path components like `../` and removes any ambiguity regarding the file's location. 
-2. Check that the canonical path is within the directory where the file should be located.