vuln-fix: Zip Slip Vulnerability

This fixes a Zip-Slip vulnerability.

This change does one of two things. This change either

1. Inserts a guard to protect against Zip Slip.
OR
2. Replaces `dir.getCanonicalPath().startsWith(parent.getCanonicalPath())`, which is vulnerable to partial path traversal attacks, with the more secure `dir.getCanonicalFile().toPath().startsWith(parent.getCanonicalFile().toPath())`.

For number 2, consider `"/usr/outnot".startsWith("/usr/out")`.
The check is bypassed although `/outnot` is not under the `/out` directory.
It's important to understand that the terminating slash may be removed when using various `String` representations of the `File` object.
For example, on Linux, `println(new File("/var"))` will print `/var`, but `println(new File("/var", "/")` will print `/var/`;
however, `println(new File("/var", "/").getCanonicalPath())` will print `/var`.

Weakness: CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
Severity: High
CVSSS: 7.4
Detection: CodeQL (https://codeql.github.com/codeql-query-help/java/java-zipslip/) & OpenRewrite (https://public.moderne.io/recipes/org.openrewrite.java.security.ZipSlip)

Reported-by: Jonathan Leitschuh <[email protected]>
Signed-off-by: Jonathan Leitschuh <[email protected]>

Bug-tracker: JLLeitschuh/security-research#16

Co-authored-by: Moderne <[email protected]>

Author: JLLeitschuh

core/src/main/java/org/projectodd/wunderboss/ApplicationRunner.java

@@ -18,10 +18,7 @@
 
 import org.slf4j.Logger;
 
-import java.io.File;
-import java.io.FileInputStream;
-import java.io.FileOutputStream;
-import java.io.InputStream;
+import java.io.*;
 import java.net.MalformedURLException;
 import java.net.URL;
 import java.net.URLConnection;
@@ -125,7 +122,10 @@ public void run() {
             if (!match) {
                 continue;
             }
-            File file = new File(extractRoot + "/" + name);
+            File file = new File(extractRoot, name);
+            if (!file.toPath().normalize().startsWith(extractRoot)) {
+                throw new IOException("Bad zip entry");
+            }
             if (zipEntry.isDirectory()) {
                 file.mkdirs();
             } else {