diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3301641..674370b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,14 @@ dan proyek ini memakai [Semantic Versioning](https://semver.org/lang/id/).
 
 ## [Unreleased]
 
+### Ditambahkan
+
+- `FileContentValidator`: tanda tangan *magic-byte* untuk ekstensi yang dulu
+  diterima RFM tetapi belum bisa diverifikasi: mpeg, mpg, wma, flv, mpga, m4a,
+  ac3, aiff, mid, iso, dmg. Pencocokan kini mendukung offset jauh (iso di
+  32769) dan offset negatif dari akhir berkas (trailer `koly` milik dmg)
+  (`OpenSID/OpenSID` #12025).
+
 ### Diperbaiki
 
 - `FileContentValidator`: alternatif `<?=` dan `<?` polos pada pemindaian
diff --git a/src/Services/FileContentValidator.php b/src/Services/FileContentValidator.php
index 599a97c..565c729 100644
--- a/src/Services/FileContentValidator.php
+++ b/src/Services/FileContentValidator.php
@@ -36,7 +36,8 @@ class FileContentValidator
      * [byteOffset, bytes] pairs that must ALL be present for that
      * alternative to match. The file is accepted if ANY alternative
      * matches. Extensions that share a container format (OOXML = zip,
-     * legacy Office = OLE2, ISO-BMFF = ftyp) share signatures.
+     * legacy Office = OLE2, ISO-BMFF = ftyp) share signatures. A negative
+     * byteOffset counts back from the end of the file (dmg's trailer).
      */
     protected const KNOWN_SIGNATURES = [
         'pdf' => [[[0, '%PDF-']], [[3, '%PDF-']]], // 2nd form tolerates a leading UTF-8 BOM
@@ -48,7 +49,18 @@ class FileContentValidator
         'rar' => [[[0, "Rar!\x1A\x07\x00"]], [[0, "Rar!\x1A\x07\x01\x00"]]],
         'gz' => [[[0, "\x1F\x8B"]]],
         'tar' => [[[257, 'ustar']]],
+        'iso' => [[[32769, 'CD001']], [[32769, 'BEA01']]], // ISO 9660 / UDF volume descriptor
+        'dmg' => [[[-512, 'koly']]], // UDIF trailer
         'mp3' => [[[0, 'ID3']], [[0, "\xFF\xFB"]], [[0, "\xFF\xF3"]], [[0, "\xFF\xF2"]], [[0, "\xFF\xFA"]], [[0, "\xFF\xE3"]]],
+        'mpga' => [[[0, 'ID3']], [[0, "\xFF\xFB"]], [[0, "\xFF\xF3"]], [[0, "\xFF\xF2"]], [[0, "\xFF\xFA"]], [[0, "\xFF\xE3"]]],
+        'm4a' => [[[4, 'ftyp']]],
+        'ac3' => [[[0, "\x0B\x77"]]],
+        'aiff' => [[[0, 'FORM'], [8, 'AIFF']], [[0, 'FORM'], [8, 'AIFC']]],
+        'mid' => [[[0, 'MThd']]],
+        'wma' => [[[0, "\x30\x26\xB2\x75\x8E\x66\xCF\x11"]]], // ASF header GUID
+        'flv' => [[[0, 'FLV']]],
+        'mpeg' => [[[0, "\x00\x00\x01\xBA"]], [[0, "\x00\x00\x01\xB3"]]], // MPEG-PS pack / sequence header
+        'mpg' => [[[0, "\x00\x00\x01\xBA"]], [[0, "\x00\x00\x01\xB3"]]],
         'ogg' => [[[0, 'OggS']]],
         'wav' => [[[0, 'RIFF'], [8, 'WAVE']]],
         'avi' => [[[0, 'RIFF'], [8, 'AVI ']]],
@@ -154,25 +166,44 @@ protected function matchesKnownSignature(string $localPath, string $extension):
             return false;
         }
 
-        // Enough for the deepest offset we check (tar's "ustar" at 257).
-        $header = (string) fread($handle, 512);
-        fclose($handle);
+        try {
+            foreach ($signatures as $alternative) {
+                $allPresent = true;
 
-        foreach ($signatures as $alternative) {
-            $allPresent = true;
+                foreach ($alternative as [$offset, $needle]) {
+                    if ($this->readAt($handle, $offset, strlen($needle)) !== $needle) {
+                        $allPresent = false;
+                        break;
+                    }
+                }
 
-            foreach ($alternative as [$offset, $needle]) {
-                if (substr($header, $offset, strlen($needle)) !== $needle) {
-                    $allPresent = false;
-                    break;
+                if ($allPresent) {
+                    return true;
                 }
             }
 
-            if ($allPresent) {
-                return true;
-            }
+            return false;
+        } finally {
+            fclose($handle);
         }
+    }
+
+    /**
+     * Reads $length bytes at $offset (negative = from the end of the file),
+     * or null when the file is too short to hold them.
+     *
+     * @param  resource  $handle
+     */
+    protected function readAt($handle, int $offset, int $length): ?string
+    {
+        $seeked = $offset < 0 ? fseek($handle, $offset, SEEK_END) : fseek($handle, $offset);
+
+        if ($seeked !== 0) {
+            return null;
+        }
+
+        $bytes = fread($handle, $length);
 
-        return false;
+        return $bytes === false ? null : $bytes;
     }
 }
diff --git a/tests/Unit/FileContentValidatorTest.php b/tests/Unit/FileContentValidatorTest.php
index e607adc..e6d3757 100644
--- a/tests/Unit/FileContentValidatorTest.php
+++ b/tests/Unit/FileContentValidatorTest.php
@@ -140,6 +140,57 @@ public function accepts_a_non_image_with_a_valid_signature(): void
         $this->assertTrue($this->validator->isValidUpload($zip, 'zip'));
     }
 
+    #[Test]
+    public function accepts_the_legacy_rfm_media_and_archive_formats_with_a_valid_signature(): void
+    {
+        $samples = [
+            'mpeg' => "\x00\x00\x01\xBA".str_repeat("\x00", 60),
+            'mpg' => "\x00\x00\x01\xB3".str_repeat("\x00", 60),
+            'wma' => "\x30\x26\xB2\x75\x8E\x66\xCF\x11\xA6\xD9\x00\xAA\x00\x62\xCE\x6C".str_repeat("\x00", 48),
+            'flv' => "FLV\x01\x05\x00\x00\x00\x09".str_repeat("\x00", 55),
+            'mpga' => 'ID3'.str_repeat("\x00", 61),
+            'm4a' => "\x00\x00\x00\x20ftypM4A ".str_repeat("\x00", 52),
+            'ac3' => "\x0B\x77".str_repeat("\x00", 62),
+            'aiff' => "FORM\x00\x00\x00\x40AIFF".str_repeat("\x00", 52),
+            'mid' => "MThd\x00\x00\x00\x06".str_repeat("\x00", 56),
+            'iso' => str_repeat("\x00", 32769).'CD001'.str_repeat("\x00", 64),
+            'dmg' => str_repeat("\x00", 1024).'koly'.str_repeat("\x00", 508),
+        ];
+
+        foreach ($samples as $extension => $bytes) {
+            $this->assertTrue($this->validator->isValidUpload($this->tempFile($bytes), $extension), "{$extension} asli harus diterima");
+        }
+    }
+
+    #[Test]
+    public function rejects_a_php_payload_disguised_as_a_legacy_rfm_format(): void
+    {
+        $path = $this->tempFile("<?php system(\$_GET['cmd']); ?>");
+
+        foreach (['mpeg', 'mpg', 'wma', 'flv', 'mpga', 'm4a', 'ac3', 'aiff', 'mid', 'iso', 'dmg'] as $extension) {
+            $this->assertFalse($this->validator->isValidUpload($path, $extension), "{$extension} palsu harus ditolak");
+        }
+    }
+
+    #[Test]
+    public function rejects_a_valid_signature_carrying_an_embedded_php_payload(): void
+    {
+        $flv = $this->tempFile("FLV\x01\x05\x00\x00\x00\x09<?php system(\$_GET['cmd']); ?>");
+        $dmg = $this->tempFile("<?php system(\$_GET['cmd']); ?>".str_repeat("\x00", 1024).'koly'.str_repeat("\x00", 508));
+
+        $this->assertFalse($this->validator->isValidUpload($flv, 'flv'));
+        $this->assertFalse($this->validator->isValidUpload($dmg, 'dmg'));
+    }
+
+    #[Test]
+    public function rejects_a_file_too_short_to_hold_a_deep_or_trailing_signature(): void
+    {
+        $path = $this->tempFile('koly');
+
+        $this->assertFalse($this->validator->isValidUpload($path, 'dmg'));
+        $this->assertFalse($this->validator->isValidUpload($path, 'iso'));
+    }
+
     #[Test]
     public function rejects_a_non_image_extension_with_no_verifiable_signature(): void
     {