Fix directory traversal vulnerability in Expand.extractFile

Co-authored-by: slachiewicz <6705942+slachiewicz@users.noreply.github.com>

Author: Copilot

src/main/java/org/codehaus/plexus/util/Expand.java

@@ -111,8 +111,18 @@ protected void extractFile(
             throws Exception {
         File f = FileUtils.resolveFile(dir, entryName);
 
-        if (!f.getAbsolutePath().startsWith(dir.getAbsolutePath())) {
-            throw new IOException("Entry '" + entryName + "' outside the target directory.");
+        // Use canonical paths to prevent bypasses via symlinks, and add separator check
+        // to prevent partial prefix matches (e.g., /tmp/app matching /tmp/app-data)
+        try {
+            String canonicalDirPath = dir.getCanonicalPath();
+            String canonicalFilePath = f.getCanonicalPath();
+
+            if (!canonicalFilePath.equals(canonicalDirPath)
+                    && !canonicalFilePath.startsWith(canonicalDirPath + File.separator)) {
+                throw new IOException("Entry '" + entryName + "' outside the target directory.");
+            }
+        } catch (IOException e) {
+            throw new IOException("Failed to validate path for entry '" + entryName + "'", e);
         }
 
         try {

src/test/java/org/codehaus/plexus/util/ExpandTest.java

@@ -0,0 +1,206 @@
+package org.codehaus.plexus.util;
+
+/*
+ * Copyright The Codehaus Foundation.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.util.zip.ZipEntry;
+import java.util.zip.ZipOutputStream;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+/**
+ * Tests for the Expand class to ensure it properly prevents directory traversal attacks.
+ */
+public class ExpandTest extends FileBasedTestCase {
+
+    /**
+     * Test that path traversal using ../ is blocked
+     */
+    @Test
+    void testPathTraversalWithParentDirectory() throws Exception {
+        File testDir = new File(getTestDirectory(), "expandTest");
+        testDir.mkdirs();
+
+        File zipFile = new File(testDir, "malicious.zip");
+        File extractDir = new File(testDir, "extract");
+        extractDir.mkdirs();
+
+        // Create a malicious zip with path traversal
+        try (ZipOutputStream zos = new ZipOutputStream(new FileOutputStream(zipFile))) {
+            ZipEntry entry = new ZipEntry("../evil.txt");
+            zos.putNextEntry(entry);
+            zos.write("malicious content".getBytes());
+            zos.closeEntry();
+        }
+
+        Expand expand = new Expand();
+        expand.setSrc(zipFile);
+        expand.setDest(extractDir);
+
+        // This should throw an IOException due to path traversal detection
+        assertThrows(
+                Exception.class, () -> expand.execute(), "Should have thrown exception for path traversal attempt");
+
+        // Verify the file was not created outside the target directory
+        File evilFile = new File(testDir, "evil.txt");
+        assertTrue(!evilFile.exists(), "File should not have been created outside target directory");
+    }
+
+    /**
+     * Test that absolute paths are blocked
+     */
+    @Test
+    void testPathTraversalWithAbsolutePath() throws Exception {
+        File testDir = new File(getTestDirectory(), "expandTest2");
+        testDir.mkdirs();
+
+        File zipFile = new File(testDir, "malicious.zip");
+        File extractDir = new File(testDir, "extract");
+        extractDir.mkdirs();
+
+        // Create a malicious zip with absolute path
+        try (ZipOutputStream zos = new ZipOutputStream(new FileOutputStream(zipFile))) {
+            ZipEntry entry = new ZipEntry("/tmp/evil.txt");
+            zos.putNextEntry(entry);
+            zos.write("malicious content".getBytes());
+            zos.closeEntry();
+        }
+
+        Expand expand = new Expand();
+        expand.setSrc(zipFile);
+        expand.setDest(extractDir);
+
+        // This should throw an IOException due to absolute path
+        assertThrows(Exception.class, () -> expand.execute(), "Should have thrown exception for absolute path");
+    }
+
+    /**
+     * Test that valid files are extracted correctly
+     */
+    @Test
+    void testValidFileExtraction() throws Exception {
+        File testDir = new File(getTestDirectory(), "expandTest3");
+        testDir.mkdirs();
+
+        File zipFile = new File(testDir, "valid.zip");
+        File extractDir = new File(testDir, "extract");
+        extractDir.mkdirs();
+
+        String testContent = "valid content";
+
+        // Create a valid zip file
+        try (ZipOutputStream zos = new ZipOutputStream(new FileOutputStream(zipFile))) {
+            ZipEntry entry = new ZipEntry("subdir/valid.txt");
+            zos.putNextEntry(entry);
+            zos.write(testContent.getBytes());
+            zos.closeEntry();
+        }
+
+        Expand expand = new Expand();
+        expand.setSrc(zipFile);
+        expand.setDest(extractDir);
+        expand.execute();
+
+        // Verify the file was created in the correct location
+        File extractedFile = new File(extractDir, "subdir/valid.txt");
+        assertTrue(extractedFile.exists(), "Valid file should have been extracted");
+        assertTrue(extractedFile.isFile(), "Extracted path should be a file");
+    }
+
+    /**
+     * Test complex path traversal attempts
+     */
+    @Test
+    void testComplexPathTraversal() throws Exception {
+        File testDir = new File(getTestDirectory(), "expandTest4");
+        testDir.mkdirs();
+
+        File zipFile = new File(testDir, "malicious.zip");
+        File extractDir = new File(testDir, "extract");
+        extractDir.mkdirs();
+
+        // Create a malicious zip with complex path traversal
+        try (ZipOutputStream zos = new ZipOutputStream(new FileOutputStream(zipFile))) {
+            // Try various path traversal techniques
+            String[] maliciousPaths = {
+                "../../evil.txt", "../../../evil.txt", "subdir/../../evil.txt", "subdir/../../../evil.txt"
+            };
+
+            for (String path : maliciousPaths) {
+                ZipEntry entry = new ZipEntry(path);
+                zos.putNextEntry(entry);
+                zos.write("malicious content".getBytes());
+                zos.closeEntry();
+            }
+        }
+
+        Expand expand = new Expand();
+        expand.setSrc(zipFile);
+        expand.setDest(extractDir);
+
+        // This should throw an IOException due to path traversal detection
+        assertThrows(
+                Exception.class,
+                () -> expand.execute(),
+                "Should have thrown exception for complex path traversal attempt");
+    }
+
+    /**
+     * Test partial path prefix match vulnerability
+     * This tests the case where the target directory is /tmp/app and an attacker
+     * tries to write to /tmp/app-data which would pass a naive startsWith check
+     */
+    @Test
+    void testPartialPrefixMatchVulnerability() throws Exception {
+        File testDir = new File(getTestDirectory(), "expandTest5");
+        testDir.mkdirs();
+
+        // Create directories with similar names
+        File extractDir = new File(testDir, "app");
+        extractDir.mkdirs();
+        File siblingDir = new File(testDir, "app-data");
+        siblingDir.mkdirs();
+
+        File zipFile = new File(testDir, "malicious.zip");
+
+        // Create a malicious zip that tries to escape to the sibling directory
+        try (ZipOutputStream zos = new ZipOutputStream(new FileOutputStream(zipFile))) {
+            ZipEntry entry = new ZipEntry("../app-data/evil.txt");
+            zos.putNextEntry(entry);
+            zos.write("malicious content".getBytes());
+            zos.closeEntry();
+        }
+
+        Expand expand = new Expand();
+        expand.setSrc(zipFile);
+        expand.setDest(extractDir);
+
+        // This should throw an IOException due to path traversal detection
+        assertThrows(
+                Exception.class,
+                () -> expand.execute(),
+                "Should have thrown exception for partial prefix match attack");
+
+        // Verify the file was not created in the sibling directory
+        File evilFile = new File(siblingDir, "evil.txt");
+        assertTrue(!evilFile.exists(), "File should not have been created in sibling directory");
+    }
+}