From 1d932cfa4ad0e5a2b6cbc60530176dc1dd864779 Mon Sep 17 00:00:00 2001
From: Git'Fellow <12234510+solracsf@users.noreply.github.com>
Date: Mon, 9 Mar 2026 18:25:26 +0100
Subject: [PATCH] fix(previex): Validate preview MIME type

Signed-off-by: Git'Fellow <12234510+solracsf@users.noreply.github.com>
---
 lib/private/Preview/Generator.php | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/lib/private/Preview/Generator.php b/lib/private/Preview/Generator.php
index 4a7341896ef6a..c0c55a44bb1d1 100644
--- a/lib/private/Preview/Generator.php
+++ b/lib/private/Preview/Generator.php
@@ -535,6 +535,9 @@ private function generatePreview(
 			self::unguardWithSemaphore($sem);
 		}
 
+		if (!$preview->valid() || $preview->dataMimeType() === null) {
+			throw new \InvalidArgumentException('Preview generation failed: invalid or null MIME type');
+		}
 
 		$path = $this->generatePath($width, $height, $crop, false, $preview->dataMimeType(), $prefix);
 		try {