vuln-fix: Partial Path Traversal Vulnerability

This fixes a partial path traversal vulnerability.

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())`.

To demonstrate this vulnerability, 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: Medium
CVSSS: 6.1
Detection: CodeQL & OpenRewrite (https://public.moderne.io/recipes/org.openrewrite.java.security.PartialPathTraversalVulnerability)

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

Bug-tracker: JLLeitschuh/security-research#13

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

src/main/java/org/apache/catalina/servlets/ManagerServlet.java

@@ -1102,15 +1102,13 @@ protected void undeploy(PrintWriter writer, String path) {
             // Identify the appBase of the owning Host of this Context (if any)
             String appBase = null;
             File appBaseDir = null;
-            String appBasePath = null;
             if (context.getParent() instanceof Host) {
                 appBase = ((Host) context.getParent()).getAppBase();
                 appBaseDir = new File(appBase);
                 if (!appBaseDir.isAbsolute()) {
                     appBaseDir = new File(System.getProperty("catalina.base"),
                                           appBase);
                 }
-                appBasePath = appBaseDir.getCanonicalPath();
             }
 
             // Validate the docBase path of this application
@@ -1121,7 +1119,7 @@ protected void undeploy(PrintWriter writer, String path) {
                 docBaseDir = new File(appBaseDir, docBase);
             }
             String docBasePath = docBaseDir.getCanonicalPath();
-            if (!docBasePath.startsWith(deployedPath)) {
+            if (!docBaseDir.getCanonicalFile().toPath().startsWith(deployedPath)) {
                 writer.println(sm.getString("managerServlet.noDocBase",
                                             displayPath));
                 return;