Potential fix for code scanning alert no. 1: Arbitrary file access during archive extraction ("Zip Slip")

[securebeats]

Potential fix for https://github.com/securebeats/skills-secure-repository-supply-chain/security/code-scanning/1

To fix this vulnerability, the code should resolve the full, absolute path of the intended destination file using Path.GetFullPath after combining the destination folder and entry name. Then, determine the absolute path of the destination directory (ensuring it ends with a path separator). Finally, check that the destination file's full path starts with the absolute destination directory path (case-sensitive comparison), and throw an exception if not. This ensures that no archive entry can escape the destination directory through directory traversal or similar path manipulation.

The changes are restricted to the WriteToDirectory method in code/src/Attendee/Attendee.cs. No new methods need to be written; only additional lines added to apply the appropriate validation before extracting the file.

Steps:

1. Replace the naive path combination with one validated by Path.GetFullPath.
2. Get the full path of the destination directory with a separator.
3. Check if the resulting file path starts with the full destination path, abort otherwise.
4. Only extract if the validation passes.

No new external dependencies are required, only standard .NET libraries already imported.

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