diff --git a/lib/Constants.php b/lib/Constants.php
index 7b09bda65..3e601a2f1 100644
--- a/lib/Constants.php
+++ b/lib/Constants.php
@@ -234,6 +234,11 @@ class Constants {
 	 */
 	public const QUESTION_EXTRASETTINGS_OTHER_PREFIX = 'system-other-answer:';
 
+	/**
+	 * Maximum number of submissions returned per paginated API request.
+	 */
+	public const SUBMISSIONS_LIMIT_MAX = 1000;
+
 	public const SUPPORTED_EXPORT_FORMATS = [
 		'csv' => 'text/csv',
 		'ods' => 'application/vnd.oasis.opendocument.spreadsheet',
diff --git a/lib/Controller/ApiController.php b/lib/Controller/ApiController.php
index 8a5797564..09bc3cb9c 100644
--- a/lib/Controller/ApiController.php
+++ b/lib/Controller/ApiController.php
@@ -1180,6 +1180,11 @@ public function getSubmissions(int $formId, ?string $query = null, ?int $limit =
 			return new DataDownloadResponse($submissionsData, $fileName, Constants::SUPPORTED_EXPORT_FORMATS[$fileFormat]);
 		}
 
+		// Cap user-supplied page size to avoid unbounded resource use
+		if ($limit !== null) {
+			$limit = max(1, min($limit, Constants::SUBMISSIONS_LIMIT_MAX));
+		}
+
 		// Load submissions and currently active questions
 		if ($canSeeAllSubmissions) {
 			$submissions = $this->submissionService->getSubmissions($formId, null, $query, $limit, $offset);
diff --git a/tests/Unit/Controller/ApiControllerTest.php b/tests/Unit/Controller/ApiControllerTest.php
index ca63507ce..453e81adc 100644
--- a/tests/Unit/Controller/ApiControllerTest.php
+++ b/tests/Unit/Controller/ApiControllerTest.php
@@ -297,6 +297,108 @@ public function testGetSubmissions(array $submissions, array $questions, array $
 		$this->assertEquals(new DataResponse($expected), $this->apiController->getSubmissions(1));
 	}
 
+	public function testGetSubmissions_limitIsCapped(): void {
+		$form = new Form();
+		$form->setId(1);
+		$form->setOwnerId('otherUser');
+
+		$this->formsService->expects($this->once())
+			->method('getFormIfAllowed')
+			->with(1, Constants::PERMISSION_RESULTS)
+			->willReturn($form);
+
+		$this->formsService->expects($this->once())
+			->method('getPermissions')
+			->with($form)
+			->willReturn([Constants::PERMISSION_RESULTS]);
+
+		// An overly large limit must be clamped to SUBMISSIONS_LIMIT_MAX
+		$this->submissionService->expects($this->once())
+			->method('getSubmissions')
+			->with(1, null, null, Constants::SUBMISSIONS_LIMIT_MAX, 0)
+			->willReturn([]);
+
+		$this->submissionMapper->expects($this->once())
+			->method('countSubmissions')
+			->with(1)
+			->willReturn(0);
+
+		$this->formsService->expects($this->once())
+			->method('getQuestions')
+			->with(1)
+			->willReturn([]);
+
+		$this->apiController->getSubmissions(1, limit: 100000);
+	}
+
+	public function testGetSubmissions_limitFloorIsOne(): void {
+		$form = new Form();
+		$form->setId(1);
+		$form->setOwnerId('otherUser');
+
+		$this->formsService->expects($this->once())
+			->method('getFormIfAllowed')
+			->with(1, Constants::PERMISSION_RESULTS)
+			->willReturn($form);
+
+		$this->formsService->expects($this->once())
+			->method('getPermissions')
+			->with($form)
+			->willReturn([Constants::PERMISSION_RESULTS]);
+
+		// A non-positive limit must be floored to 1
+		$this->submissionService->expects($this->once())
+			->method('getSubmissions')
+			->with(1, null, null, 1, 0)
+			->willReturn([]);
+
+		$this->submissionMapper->expects($this->once())
+			->method('countSubmissions')
+			->with(1)
+			->willReturn(0);
+
+		$this->formsService->expects($this->once())
+			->method('getQuestions')
+			->with(1)
+			->willReturn([]);
+
+		$this->apiController->getSubmissions(1, limit: 0);
+	}
+
+	public function testGetSubmissions_nullLimitStaysNull(): void {
+		$form = new Form();
+		$form->setId(1);
+		$form->setOwnerId('otherUser');
+
+		$this->formsService->expects($this->once())
+			->method('getFormIfAllowed')
+			->with(1, Constants::PERMISSION_RESULTS)
+			->willReturn($form);
+
+		$this->formsService->expects($this->once())
+			->method('getPermissions')
+			->with($form)
+			->willReturn([Constants::PERMISSION_RESULTS]);
+
+		// null limit is preserved so the summary view can load all submissions
+		$this->submissionService->expects($this->once())
+			->method('getSubmissions')
+			->with(1, null, null, null, 0)
+			->willReturn([]);
+
+		$this->submissionMapper->expects($this->once())
+			->method('countSubmissions')
+			->with(1)
+			->willReturn(0);
+
+		$this->formsService->expects($this->once())
+			->method('getQuestions')
+			->with(1)
+			->willReturn([]);
+
+		$this->apiController->getSubmissions(1);
+	}
+
 	public function testExportSubmissions_invalidForm() {
 		$this->formsService->expects($this->once())
 			->method('getFormIfAllowed')