Error if installed plugin is inside plugins folder

distribution/tools/plugin-cli/src/main/java/org/elasticsearch/plugins/cli/InstallPluginAction.java

@@ -63,6 +63,7 @@
 import java.nio.file.FileVisitResult;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.nio.file.Paths;
 import java.nio.file.SimpleFileVisitor;
 import java.nio.file.StandardCopyOption;
 import java.nio.file.attribute.BasicFileAttributes;
@@ -329,10 +330,31 @@ private Path download(InstallablePlugin plugin, Path tmpDir) throws Exception {
             }
             throw new UserException(ExitCodes.USAGE, msg);
         }
+
+        verifyLocationNotInPluginsDirectory(pluginLocation);
+
         terminal.println(logPrefix + "Downloading " + URLDecoder.decode(pluginLocation, StandardCharsets.UTF_8));
         return downloadZip(pluginLocation, tmpDir);
     }
 
+    @SuppressForbidden(reason = "Need to use Paths#get")
+    private void verifyLocationNotInPluginsDirectory(String pluginLocation) throws URISyntaxException, IOException, UserException {
+        if (pluginLocation == null) {
+            return;
+        }
+        URI uri = new URI(pluginLocation);
+        if ("file".equalsIgnoreCase(uri.getScheme())) {
+            Path pluginRealPath = Paths.get(uri).toRealPath();
+            Path pluginsDirectory = env.pluginsDir().toRealPath();
+            if (pluginRealPath.startsWith(pluginsDirectory)) {
+                throw new UserException(
+                    ExitCodes.USAGE,
+                    "Installation of plugin in location [" + pluginLocation + "] from inside the plugins directory is not permitted."
+                );
+            }
+        }
+    }
+
     @SuppressForbidden(reason = "Need to use PathUtils#get")
     private Path getPluginArchivePath(String pluginId, String pluginArchiveDir) throws UserException {
         final Path path = PathUtils.get(pluginArchiveDir);
@@ -462,9 +484,9 @@ private static List<String> checkMisspelledPlugin(String pluginId) {
     /** Downloads a zip from the url, into a temp file under the given temp dir. */
     // pkg private for tests
     @SuppressForbidden(reason = "We use getInputStream to download plugins")
-    Path downloadZip(String urlString, Path tmpDir) throws IOException {
+    Path downloadZip(String urlString, Path tmpDir) throws IOException, URISyntaxException {
         terminal.println(VERBOSE, "Retrieving zip from " + urlString);
-        URL url = new URL(urlString);
+        URL url = new URI(urlString).toURL();
         Path zip = Files.createTempFile(tmpDir, null, ".zip");
         URLConnection urlConnection = this.proxy == null ? url.openConnection() : url.openConnection(this.proxy);
         urlConnection.addRequestProperty("User-Agent", "elasticsearch-plugin-installer");
@@ -548,9 +570,10 @@ private InputStream urlOpenStream(final URL url) throws IOException {
      * @throws IOException   if an I/O exception occurs download or reading files and resources
      * @throws PGPException  if an exception occurs verifying the downloaded ZIP signature
      * @throws UserException if checksum validation fails
+     * @throws URISyntaxException is the url is invalid
      */
     private Path downloadAndValidate(final String urlString, final Path tmpDir, final boolean officialPlugin) throws IOException,
-        PGPException, UserException {
+        PGPException, UserException, URISyntaxException {
         Path zip = downloadZip(urlString, tmpDir);
         pathsToDeleteOnShutdown.add(zip);
         String checksumUrlString = urlString + ".sha512";

distribution/tools/plugin-cli/src/test/java/org/elasticsearch/plugins/cli/InstallPluginActionTests.java

@@ -66,18 +66,18 @@
 import java.io.BufferedReader;
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
-import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.StringReader;
-import java.net.MalformedURLException;
 import java.net.URI;
+import java.net.URISyntaxException;
 import java.net.URL;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.DirectoryStream;
 import java.nio.file.FileAlreadyExistsException;
 import java.nio.file.FileSystem;
 import java.nio.file.Files;
+import java.nio.file.NoSuchFileException;
 import java.nio.file.Path;
 import java.nio.file.StandardCopyOption;
 import java.nio.file.attribute.GroupPrincipal;
@@ -552,8 +552,8 @@ public void testTransaction() throws Exception {
             pluginZip.getId() + "-does-not-exist",
             pluginZip.getLocation() + "-does-not-exist"
         );
-        final FileNotFoundException e = expectThrows(
-            FileNotFoundException.class,
+        final NoSuchFileException e = expectThrows(
+            NoSuchFileException.class,
             () -> installPlugins(List.of(pluginZip, nonexistentPluginZip), env.v1())
         );
         assertThat(e.getMessage(), containsString("does-not-exist"));
@@ -586,11 +586,27 @@ public void testSpaceInUrl() throws Exception {
         assertPlugin("fake", pluginDir, env.v2());
     }
 
+    public void testCannotInstallFromInsidePluginsDirectory() throws Exception {
+        InstallablePlugin pluginZip = createPluginZip("fake", pluginDir);
+        Path pluginZipInsidePlugins = env.v2().pluginsDir().resolve("fake.zip");
+        try (InputStream in = FileSystemUtils.openFileURLStream(new URL(pluginZip.getLocation()))) {
+            Files.copy(in, pluginZipInsidePlugins, StandardCopyOption.REPLACE_EXISTING);
+        }
+        String location = pluginZipInsidePlugins.toUri().toURL().toString();
+        assumeTrue("requires file URL scheme", location.startsWith("file:"));
+        InstallablePlugin modifiedPlugin = new InstallablePlugin("fake", location);
+        UserException e = expectThrows(UserException.class, () -> installPlugin(modifiedPlugin));
+        assertThat(
+            e.getMessage(),
+            startsWith("Installation of plugin in location [" + location + "] from inside the plugins directory is not permitted.")
+        );
+    }
+
     public void testMalformedUrlNotMaven() {
         // has two colons, so it appears similar to maven coordinates
         InstallablePlugin plugin = new InstallablePlugin("fake", "://host:1234");
-        MalformedURLException e = expectThrows(MalformedURLException.class, () -> installPlugin(plugin));
-        assertThat(e.getMessage(), containsString("no protocol"));
+        URISyntaxException e = expectThrows(URISyntaxException.class, () -> installPlugin(plugin));
+        assertThat(e.getMessage(), containsString("Expected scheme name"));
     }
 
     public void testFileNotMaven() {

docs/changelog/137398.yaml

@@ -0,0 +1,6 @@
+pr: 137398
+summary: Error if installed plugin is inside plugins folder
+area: Infra/Plugins
+type: enhancement
+issues:
+ - 27401