diff --git a/apps/files_external/composer/composer/autoload_classmap.php b/apps/files_external/composer/composer/autoload_classmap.php
index 6cb11dc66fe85..e43059be5741f 100644
--- a/apps/files_external/composer/composer/autoload_classmap.php
+++ b/apps/files_external/composer/composer/autoload_classmap.php
@@ -86,6 +86,7 @@
     'OCA\\Files_External\\Lib\\MissingDependency' => $baseDir . '/../lib/Lib/MissingDependency.php',
     'OCA\\Files_External\\Lib\\Notify\\SMBNotifyHandler' => $baseDir . '/../lib/Lib/Notify/SMBNotifyHandler.php',
     'OCA\\Files_External\\Lib\\PersonalMount' => $baseDir . '/../lib/Lib/PersonalMount.php',
+    'OCA\\Files_External\\Lib\\PortHelper' => $baseDir . '/../lib/Lib/PortHelper.php',
     'OCA\\Files_External\\Lib\\PriorityTrait' => $baseDir . '/../lib/Lib/PriorityTrait.php',
     'OCA\\Files_External\\Lib\\SessionStorageWrapper' => $baseDir . '/../lib/Lib/SessionStorageWrapper.php',
     'OCA\\Files_External\\Lib\\StorageConfig' => $baseDir . '/../lib/Lib/StorageConfig.php',
diff --git a/apps/files_external/composer/composer/autoload_static.php b/apps/files_external/composer/composer/autoload_static.php
index 132da2a2eff10..eec146d463571 100644
--- a/apps/files_external/composer/composer/autoload_static.php
+++ b/apps/files_external/composer/composer/autoload_static.php
@@ -101,6 +101,7 @@ class ComposerStaticInitFiles_External
         'OCA\\Files_External\\Lib\\MissingDependency' => __DIR__ . '/..' . '/../lib/Lib/MissingDependency.php',
         'OCA\\Files_External\\Lib\\Notify\\SMBNotifyHandler' => __DIR__ . '/..' . '/../lib/Lib/Notify/SMBNotifyHandler.php',
         'OCA\\Files_External\\Lib\\PersonalMount' => __DIR__ . '/..' . '/../lib/Lib/PersonalMount.php',
+        'OCA\\Files_External\\Lib\\PortHelper' => __DIR__ . '/..' . '/../lib/Lib/PortHelper.php',
         'OCA\\Files_External\\Lib\\PriorityTrait' => __DIR__ . '/..' . '/../lib/Lib/PriorityTrait.php',
         'OCA\\Files_External\\Lib\\SessionStorageWrapper' => __DIR__ . '/..' . '/../lib/Lib/SessionStorageWrapper.php',
         'OCA\\Files_External\\Lib\\StorageConfig' => __DIR__ . '/..' . '/../lib/Lib/StorageConfig.php',
diff --git a/apps/files_external/lib/Lib/PortHelper.php b/apps/files_external/lib/Lib/PortHelper.php
new file mode 100644
index 0000000000000..f68bd882a4ec2
--- /dev/null
+++ b/apps/files_external/lib/Lib/PortHelper.php
@@ -0,0 +1,48 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\Files_External\Lib;
+
+/**
+ * Helper to turn a configured port into a usable TCP port number.
+ *
+ * The external storage settings store whatever the admin typed into the port
+ * field, so the value can be missing, an empty string, a non-numeric string or
+ * a number outside of the valid TCP port range.
+ */
+final class PortHelper {
+	/** Lowest valid TCP port */
+	public const MIN_PORT = 1;
+
+	/** Highest valid TCP port */
+	public const MAX_PORT = 65535;
+
+	/**
+	 * Parse a configured port value
+	 *
+	 * @param mixed $port the configured value, may be of any type
+	 * @param int $fallback port to use when the configured value is not a valid TCP port
+	 * @return int the configured port, or $fallback if it is not an integer within the valid TCP port range
+	 */
+	public static function parsePort(mixed $port, int $fallback): int {
+		if (is_int($port)) {
+			$parsedPort = $port;
+		} elseif (is_string($port) && preg_match('/^\d+$/', $port) === 1) {
+			$parsedPort = (int)$port;
+		} else {
+			return $fallback;
+		}
+
+		if ($parsedPort < self::MIN_PORT || $parsedPort > self::MAX_PORT) {
+			return $fallback;
+		}
+
+		return $parsedPort;
+	}
+}
diff --git a/apps/files_external/lib/Lib/Storage/FTP.php b/apps/files_external/lib/Lib/Storage/FTP.php
index 66e623e5a1b2c..f8cc6a1f2879a 100644
--- a/apps/files_external/lib/Lib/Storage/FTP.php
+++ b/apps/files_external/lib/Lib/Storage/FTP.php
@@ -12,6 +12,7 @@
 use Icewind\Streams\IteratorDirectory;
 use OC\Files\Storage\Common;
 use OC\Files\Storage\PolyFill\CopyDirectory;
+use OCA\Files_External\Lib\PortHelper;
 use OCP\Constants;
 use OCP\Files\FileInfo;
 use OCP\Files\IMimeTypeDetector;
@@ -23,6 +24,8 @@
 class FTP extends Common {
 	use CopyDirectory;
 
+	private const DEFAULT_PORT = 21;
+
 	private $root;
 	private $host;
 	private $password;
@@ -49,8 +52,7 @@ public function __construct(array $parameters) {
 				$this->secure = false;
 			}
 			$this->root = isset($parameters['root']) ? '/' . ltrim($parameters['root']) : '/';
-			$parsedPort = $parameters['port'] ?? null;
-			$this->port = is_numeric($parsedPort) ? (int)$parsedPort : 21;
+			$this->port = PortHelper::parsePort($parameters['port'] ?? null, self::DEFAULT_PORT);
 			$this->utf8Mode = isset($parameters['utf8']) && $parameters['utf8'];
 		} else {
 			throw new \Exception('Creating ' . self::class . ' storage failed, required parameters not set');
diff --git a/apps/files_external/lib/Lib/Storage/SFTP.php b/apps/files_external/lib/Lib/Storage/SFTP.php
index b1b5be38dbea3..034cd0729612c 100644
--- a/apps/files_external/lib/Lib/Storage/SFTP.php
+++ b/apps/files_external/lib/Lib/Storage/SFTP.php
@@ -14,6 +14,7 @@
 use Icewind\Streams\RetryWrapper;
 use OC\Files\Storage\Common;
 use OC\Files\View;
+use OCA\Files_External\Lib\PortHelper;
 use OCP\Cache\CappedMemoryCache;
 use OCP\Constants;
 use OCP\Files\FileInfo;
@@ -26,10 +27,12 @@
  * provide access to SFTP servers.
  */
 class SFTP extends Common {
+	private const DEFAULT_PORT = 22;
+
 	private $host;
 	private $user;
 	private $root;
-	private $port = 22;
+	private $port = self::DEFAULT_PORT;
 
 	private $auth = [];
 
@@ -56,11 +59,11 @@ private function splitHost(string $host): array {
 
 		$parsed = parse_url($host);
 		if (is_array($parsed) && isset($parsed['port'])) {
-			return [$parsed['host'], $parsed['port']];
+			return [$parsed['host'], PortHelper::parsePort($parsed['port'], self::DEFAULT_PORT)];
 		} elseif (is_array($parsed)) {
-			return [$parsed['host'], 22];
+			return [$parsed['host'], self::DEFAULT_PORT];
 		} else {
-			return [$input, 22];
+			return [$input, self::DEFAULT_PORT];
 		}
 	}
 
@@ -78,10 +81,9 @@ public function __construct(array $parameters) {
 		$parsedHost = $this->splitHost($parameters['host']);
 		$this->host = $parsedHost[0];
 
-		// Handle empty port parameter to allow host-defined ports
-		// and ensure strictly numeric ports
-		$parsedPort = $parameters['port'] ?? null;
-		$this->port = (int)(is_numeric($parsedPort) ? $parsedPort : $parsedHost[1]);
+		// Fall back to the port from the host field, and to the default port,
+		// unless a valid port is configured
+		$this->port = PortHelper::parsePort($parameters['port'] ?? null, $parsedHost[1]);
 
 		if (!isset($parameters['user'])) {
 			throw new \UnexpectedValueException('no authentication parameters specified');
diff --git a/apps/files_external/tests/FtpTest.php b/apps/files_external/tests/FtpTest.php
index 68e6bb723756f..21f8b1659fc0f 100644
--- a/apps/files_external/tests/FtpTest.php
+++ b/apps/files_external/tests/FtpTest.php
@@ -28,6 +28,11 @@ public static function portProvider(): array {
 			'non numeric port' => [array_merge($parameters, ['port' => 'ftp']), 21],
 			'numeric string port' => [array_merge($parameters, ['port' => '2121']), 2121],
 			'integer port' => [array_merge($parameters, ['port' => 2121]), 2121],
+			'decimal port' => [array_merge($parameters, ['port' => '21.5']), 21],
+			'zero port' => [array_merge($parameters, ['port' => '0']), 21],
+			'negative port' => [array_merge($parameters, ['port' => '-2121']), 21],
+			'out of range port' => [array_merge($parameters, ['port' => '65536']), 21],
+			'highest valid port' => [array_merge($parameters, ['port' => '65535']), 65535],
 		];
 	}
 
diff --git a/apps/files_external/tests/PortHelperTest.php b/apps/files_external/tests/PortHelperTest.php
new file mode 100644
index 0000000000000..3eef97dff2a85
--- /dev/null
+++ b/apps/files_external/tests/PortHelperTest.php
@@ -0,0 +1,63 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\Files_External\Tests;
+
+use OCA\Files_External\Lib\PortHelper;
+use PHPUnit\Framework\Attributes\DataProvider;
+use Test\TestCase;
+
+class PortHelperTest extends TestCase {
+	public static function portProvider(): array {
+		return [
+			// valid ports are returned as integers
+			'integer port' => [2121, 2121],
+			'numeric string port' => ['2121', 2121],
+			'padded numeric string port' => ['0022', 22],
+			'lowest valid port' => [1, 1],
+			'highest valid port' => [65535, 65535],
+			'highest valid port as string' => ['65535', 65535],
+
+			// unset or empty values fall back
+			'null port' => [null, 21],
+			'empty port' => ['', 21],
+			'whitespace port' => [' ', 21],
+			'array port' => [[2121], 21],
+
+			// non integer values fall back
+			'non numeric port' => ['ftp', 21],
+			'float port' => [21.5, 21],
+			'integer float port' => [2121.0, 21],
+			'decimal string port' => ['21.5', 21],
+			'exponential string port' => ['1e3', 21],
+			'hexadecimal string port' => ['0x15', 21],
+			'signed string port' => ['+2121', 21],
+			'padded string port' => [' 2121', 21],
+			'boolean port' => [true, 21],
+
+			// out of range values fall back
+			'zero port' => [0, 21],
+			'zero string port' => ['0', 21],
+			'negative port' => [-2121, 21],
+			'negative string port' => ['-2121', 21],
+			'too large port' => [65536, 21],
+			'too large string port' => ['65536', 21],
+			'way too large string port' => ['999999999999999999999999', 21],
+		];
+	}
+
+	#[DataProvider('portProvider')]
+	public function testParsePort(mixed $port, int $expectedPort): void {
+		$this->assertSame($expectedPort, PortHelper::parsePort($port, 21));
+	}
+
+	public function testParsePortReturnsGivenFallback(): void {
+		$this->assertSame(22, PortHelper::parsePort('', 22));
+	}
+}
diff --git a/apps/files_external/tests/SftpPortTest.php b/apps/files_external/tests/SftpPortTest.php
new file mode 100644
index 0000000000000..b032be09e23db
--- /dev/null
+++ b/apps/files_external/tests/SftpPortTest.php
@@ -0,0 +1,51 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\Files_External\Tests;
+
+use OCA\Files_External\Lib\Storage\SFTP;
+use PHPUnit\Framework\Attributes\DataProvider;
+use Test\TestCase;
+
+class SftpPortTest extends TestCase {
+	public static function portProvider(): array {
+		$parameters = [
+			'host' => 'somehost',
+			'user' => 'someuser',
+			'password' => 'somepassword',
+		];
+
+		return [
+			'no port given' => [$parameters, 22],
+			'empty port' => [array_merge($parameters, ['port' => '']), 22],
+			'null port' => [array_merge($parameters, ['port' => null]), 22],
+			'non numeric port' => [array_merge($parameters, ['port' => 'sftp']), 22],
+			'numeric string port' => [array_merge($parameters, ['port' => '2222']), 2222],
+			'integer port' => [array_merge($parameters, ['port' => 2222]), 2222],
+			'decimal port' => [array_merge($parameters, ['port' => '22.5']), 22],
+			'zero port' => [array_merge($parameters, ['port' => '0']), 22],
+			'negative port' => [array_merge($parameters, ['port' => '-2222']), 22],
+			'out of range port' => [array_merge($parameters, ['port' => '65536']), 22],
+			'highest valid port' => [array_merge($parameters, ['port' => '65535']), 65535],
+
+			// the port can also be part of the host field
+			'port in host' => [array_merge($parameters, ['host' => 'somehost:2222']), 2222],
+			'port in host with empty port' => [array_merge($parameters, ['host' => 'somehost:2222', 'port' => '']), 2222],
+			'port in host overwritten by port' => [array_merge($parameters, ['host' => 'somehost:2222', 'port' => '2223']), 2223],
+			'port in host with invalid port' => [array_merge($parameters, ['host' => 'somehost:2222', 'port' => '65536']), 2222],
+		];
+	}
+
+	#[DataProvider('portProvider')]
+	public function testPort(array $parameters, int $expectedPort): void {
+		$instance = new SFTP($parameters);
+
+		$this->assertSame($expectedPort, self::invokePrivate($instance, 'port'));
+	}
+}