Added secure-coding_dotNet.md

cheatsheets/security/secure-coding/secure-coding_dotNet.md

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+---
+title: Secure Coding .NET
+categories: [cheatsheets]
+tags: [topic]
+---
+
+# Secure Coding .NET
+
+## Path Traversal
+
+
+## ZIP Slip
+
+* Vulnerable (but common) implementation
+* This is also recommended when using the SharpZIP Library
+    - [https://github.com/icsharpcode/SharpZipLib/wiki/Unpack-a-Zip-with-full-control-over-the-operation](https://github.com/icsharpcode/SharpZipLib/wiki/Unpack-a-Zip-with-full-control-over-the-operation]
+
+
+
+```C#
+using (ZipFile zipFile = new ZipFile(filename))  // filename = C:\SomePath\malicious.IFXRep
+{
+    zipFile.Password = null;
+    foreach (object obj in zipFile)
+    {
+        ZipEntry zipEntry = (ZipEntry)obj; // zipEntry loops every File in the Archive
+        if (zipEntry.IsFile)
+        {
+            string name = zipEntry.Name; // name = ..\..\..\..\..\..\malicous\path\traversal\malicious.exe"
+            byte[] buffer = new byte[4096];
+            Stream inputStream = zipFile.GetInputStream(zipEntry);
+
+
+            /*
+                This is the dangerous part! The Path Traversal and the extraction path are combined.
+                -> "C:\EasyApe\extract\<pid>" +  "..\..\..\" = Malicious Path Traversal
+                The vulnerability here is in the usage of the library and not in the library itself.
+            */
+            string path2 = Path.Combine(path, name);
+
+            string directoryName = Path.GetDirectoryName(path2);
+            if (directoryName != null && directoryName.Length > 0)
+            {
+                    Directory.CreateDirectory(directoryName);
+            }
+            using (FileStream fileStream = File.Create(path2))
+            {
+                    StreamUtils.Copy(inputStream, fileStream, buffer);
+            }
+        }
+    }
+}
+```
+
+A fast way of doing this correctly:
+
+```C#
+using (FastZip zipFile = new FastZip()) {
+    zipFile.ExtractZip(filename, "%APPDATA%\Local\EasyAPEPro\EasyAPE\extract\<pid>\")
+}
+```
+