diff --git a/src/Attachment.php b/src/Attachment.php
index ca99f5f22..b54f97a22 100644
--- a/src/Attachment.php
+++ b/src/Attachment.php
@@ -2,6 +2,7 @@
 
 namespace Timber;
 
+use InvalidArgumentException;
 use Timber\Factory\PostFactory;
 
 /**
@@ -245,6 +246,10 @@ public function size(): ?int
             return $this->size = (int) $size;
         }
 
+        if (!ImageHelper::is_protocol_allowed($this->file_loc())) {
+            throw new InvalidArgumentException('The output file scheme is not supported.');
+        }
+
         /**
          * Filesize wasn't found in the metadata, so we'll try to get it from the file itself.
          *
diff --git a/src/Image/Operation/ToJpg.php b/src/Image/Operation/ToJpg.php
index 6f768e8b0..e45e9e4c3 100644
--- a/src/Image/Operation/ToJpg.php
+++ b/src/Image/Operation/ToJpg.php
@@ -2,6 +2,7 @@
 
 namespace Timber\Image\Operation;
 
+use InvalidArgumentException;
 use Timber\Image\Operation as ImageOperation;
 use Timber\ImageHelper;
 
@@ -44,6 +45,10 @@ public function filename($src_filename, $src_extension = 'jpg')
      */
     public function run($load_filename, $save_filename)
     {
+        if (!ImageHelper::is_protocol_allowed($load_filename)) {
+            throw new InvalidArgumentException('The output file scheme is not supported.');
+        }
+
         if (!\file_exists($load_filename)) {
             return false;
         }
diff --git a/src/Image/Operation/ToWebp.php b/src/Image/Operation/ToWebp.php
index 11b4ba5a9..abd573ae8 100644
--- a/src/Image/Operation/ToWebp.php
+++ b/src/Image/Operation/ToWebp.php
@@ -2,6 +2,7 @@
 
 namespace Timber\Image\Operation;
 
+use InvalidArgumentException;
 use Timber\Helper;
 use Timber\Image\Operation as ImageOperation;
 use Timber\ImageHelper;
@@ -45,6 +46,10 @@ public function filename($src_filename, $src_extension = 'webp')
      */
     public function run($load_filename, $save_filename)
     {
+        if (!ImageHelper::is_protocol_allowed($load_filename)) {
+            throw new InvalidArgumentException('The output file scheme is not supported.');
+        }
+
         if (!\is_file($load_filename)) {
             return false;
         }
diff --git a/src/ImageDimensions.php b/src/ImageDimensions.php
index ee2babcb7..c92bf8dab 100644
--- a/src/ImageDimensions.php
+++ b/src/ImageDimensions.php
@@ -2,6 +2,8 @@
 
 namespace Timber;
 
+use InvalidArgumentException;
+
 /**
  * Class FileSize
  *
@@ -117,6 +119,10 @@ public function get_dimension($dimension): ?int
             return $this->get_dimension_loaded($dimension);
         }
 
+        if (!ImageHelper::is_protocol_allowed($this->file_loc)) {
+            throw new InvalidArgumentException('The output file scheme is not supported.');
+        }
+
         // Load dimensions.
         if (\file_exists($this->file_loc) && \filesize($this->file_loc)) {
             if (ImageHelper::is_svg($this->file_loc)) {
diff --git a/src/ImageHelper.php b/src/ImageHelper.php
index 90945a55b..a6abad014 100644
--- a/src/ImageHelper.php
+++ b/src/ImageHelper.php
@@ -2,6 +2,7 @@
 
 namespace Timber;
 
+use InvalidArgumentException;
 use Timber\Image\Operation;
 
 /**
@@ -29,6 +30,10 @@ class ImageHelper
 
     public static $home_url;
 
+    protected const ALLOWED_PROTOCOLS = ['file', 'http', 'https'];
+
+    protected const WINDOWS_LOCAL_FILENAME_REGEX = '/^[a-z]:(?:[\\\\\/]?(?:[\w\s!#()-]+|[\.]{1,2})+)*[\\\\\/]?/i';
+
     /**
      * Inits the object.
      */
@@ -140,6 +145,11 @@ public static function is_animated_gif($file)
             //doesn't have .gif, bail
             return false;
         }
+
+        if (!ImageHelper::is_protocol_allowed($file)) {
+            throw new InvalidArgumentException('The output file scheme is not supported.');
+        }
+
         // Its a gif so test
         if (!($fh = @\fopen($file, 'rb'))) {
             return false;
@@ -169,7 +179,15 @@ public static function is_animated_gif($file)
      */
     public static function is_svg($file_path)
     {
-        if ('' === $file_path || !\file_exists($file_path)) {
+        if ('' === $file_path) {
+            return false;
+        }
+
+        if (!ImageHelper::is_protocol_allowed($file_path)) {
+            throw new InvalidArgumentException('The output file scheme is not supported.');
+        }
+
+        if (!\file_exists($file_path)) {
             return false;
         }
 
@@ -431,6 +449,10 @@ public static function get_sideloaded_file_loc($file)
      */
     public static function sideload_image($file)
     {
+        if (!ImageHelper::is_protocol_allowed($file)) {
+            throw new InvalidArgumentException('The output file scheme is not supported.');
+        }
+
         /**
          * Adds a filter to change the upload folder temporarily.
          *
@@ -444,6 +466,7 @@ public static function sideload_image($file)
         \add_filter('upload_dir', [__CLASS__, 'set_sideload_image_upload_dir']);
 
         $loc = self::get_sideloaded_file_loc($file);
+
         if (\file_exists($loc)) {
             $url = URLHelper::file_system_to_url($loc);
 
@@ -806,6 +829,10 @@ private static function _operate($src, $op, $force = false)
             return '';
         }
 
+        if (!ImageHelper::is_protocol_allowed($src)) {
+            throw new InvalidArgumentException('The output file scheme is not supported.');
+        }
+
         $allow_fs_write = \apply_filters('timber/allow_fs_write', true);
 
         if ($allow_fs_write === false) {
@@ -949,4 +976,36 @@ public static function get_resize_file_path($url, $w, $h, $crop)
         );
         return $new_path;
     }
+
+    /**
+     * Checks if the protocol of the given filename is allowed.
+     *
+     * This fixes a security issue with a PHAR deserialization vulnerability
+     * with file_exists() in PHP < 8.0.0.
+     *
+     * @param  string $filepath File path.
+     * @return bool
+     */
+    public static function is_protocol_allowed($filepath)
+    {
+        $parsed_url = \parse_url($filepath);
+
+        if (false === $parsed_url) {
+            throw new InvalidArgumentException('The filename is not valid.');
+        }
+
+        $protocol = isset($parsed_url['scheme'])
+            ? \mb_strtolower($parsed_url['scheme'])
+            : 'file';
+
+        if (
+            \PHP_OS_FAMILY === 'Windows'
+            && \strlen($protocol) === 1
+            && \preg_match(self::WINDOWS_LOCAL_FILENAME_REGEX, $filepath)
+        ) {
+            $protocol = 'file';
+        }
+
+        return \in_array($protocol, self::ALLOWED_PROTOCOLS, true);
+    }
 }
diff --git a/src/Timber.php b/src/Timber.php
index eded41497..3d01fd154 100644
--- a/src/Timber.php
+++ b/src/Timber.php
@@ -2,6 +2,7 @@
 
 namespace Timber;
 
+use InvalidArgumentException;
 use Timber\Factory\CommentFactory;
 use Timber\Factory\MenuFactory;
 use Timber\Factory\PagesMenuFactory;
@@ -659,6 +660,10 @@ public static function get_attachment_by(string $field_or_ident, string $ident =
                 return null;
             }
 
+            if (!ImageHelper::is_protocol_allowed($ident)) {
+                throw new InvalidArgumentException('The output file scheme is not supported.');
+            }
+
             if (!\file_exists($ident)) {
                 // Deal with a relative path.
                 $ident = URLHelper::get_full_path($ident);
diff --git a/tests/test-timber-image.php b/tests/test-timber-image.php
index 8c4d09786..822f721ec 100644
--- a/tests/test-timber-image.php
+++ b/tests/test-timber-image.php
@@ -1185,4 +1185,54 @@ public function testSVGDimensions()
         $this->assertSame(23, $image->width());
         $this->assertSame(20, $image->height());
     }
+
+    public function testPharProtocolIsNotAllowedwithResize()
+    {
+        $object = new ImageOperation\Resize(400, 300, 'center');
+        $load_filename = 'phar://test.jpg';
+        $save_filename = 'test-new.jpg';
+
+        $this->expectException(InvalidArgumentException::class);
+        $object->run($load_filename, $save_filename);
+    }
+
+    public function testPharProtocolIsNotAllowedwithLetterbox()
+    {
+        $object = new ImageOperation\Letterbox(400, 300, '#FFFFFF');
+        $load_filename = 'phar://test.jpg';
+        $save_filename = 'test-new.jpg';
+
+        $this->expectException(InvalidArgumentException::class);
+        $object->run($load_filename, $save_filename);
+    }
+
+    public function testPharProtocolIsNotAllowedwithRetina()
+    {
+        $object = new ImageOperation\Retina(2);
+        $load_filename = 'phar://test.jpg';
+        $save_filename = 'test-new.jpg';
+
+        $this->expectException(InvalidArgumentException::class);
+        $object->run($load_filename, $save_filename);
+    }
+
+    public function testPharProtocolIsNotAllowedwithToJpg()
+    {
+        $object = new ImageOperation\ToJpg('#FFFFFF');
+        $load_filename = 'phar://test.svg';
+        $save_filename = 'test-new.svg';
+
+        $this->expectException(InvalidArgumentException::class);
+        $object->run($load_filename, $save_filename);
+    }
+
+    public function testPharProtocolIsNotAllowedwithToWebp()
+    {
+        $object = new ImageOperation\ToWebp(80);
+        $load_filename = 'phar://test.png';
+        $save_filename = 'test-new.png';
+
+        $this->expectException(InvalidArgumentException::class);
+        $object->run($load_filename, $save_filename);
+    }
 }