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]>

src/main/java/org/dtk/util/FileUtil.java

@@ -221,7 +221,11 @@ public static boolean inflateZipFile(String baseDirectory, InputStream is) {
 					File dirFile = new File(baseDirectory, zipEntry.getName());	
 					dirFile.mkdir();
 				} else {
-					FileOutputStream fout = new FileOutputStream(new File(baseDirectory, zipEntry.getName()));		        	
+					final File zipEntryFile = new File(baseDirectory, zipEntry.getName());
+					if (!zipEntryFile.toPath().normalize().startsWith(baseDirectory)) {
+						throw new RuntimeException("Bad zip entry");
+					}
+					FileOutputStream fout = new FileOutputStream(zipEntryFile);		        	
 					for (int c = zis.read(); c != -1; c = zis.read()) {
 						fout.write(c);
 					}