Strip EXIF/GPS metadata from image uploads (#97)

api/upload_attachment.php did a raw move_uploaded_file() with zero
image processing. A photo attached from a phone retained embedded
EXIF, including GPS coordinates, and download_attachment.php streams
the file byte-for-byte back to any user with ticket visibility — for
an infrastructure company, this could leak a data center or office's
precise physical location through a routine ticket photo, especially
on Confidential-visibility tickets whose whole point is restricting
exactly this kind of detail.

Added stripImageMetadata(): decodes and re-encodes JPEG/PNG/GIF/WebP
uploads via GD, which drops EXIF chunks that aren't part of the pixel
data. Best-effort — leaves the file untouched on any failure (corrupt
image, unsupported format, GD unavailable, or an oversized decoded
pixel count guarding against a decompression-bomb-style crafted image)
rather than blocking the upload.

Verified with a real GPS-tagged JPEG (generated via piexif) and a
GD/PHP harness: GPS EXIF is gone after stripping, the image stays
valid and correctly sized, PNG alpha transparency is preserved, and
corrupt files / non-image MIME types are left byte-for-byte unchanged.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MGDKHiU5RJdo3dqQUDow3X

api/upload_attachment.php

@@ -29,6 +29,73 @@ require_once dirname(__DIR__) . '/middleware/CsrfMiddleware.php';
 
 header('Content-Type: application/json');
 
+/**
+ * Strip EXIF/metadata (including GPS) from an image file in place by
+ * decoding and re-encoding it via GD, which drops metadata chunks that
+ * aren't part of the pixel data. Best-effort: leaves the file untouched on
+ * any failure (corrupt image, unsupported format, GD unavailable) rather
+ * than blocking the upload — original bytes are what would have been stored
+ * anyway before this existed.
+ *
+ * download_attachment.php streams attachments back byte-for-byte to any user
+ * with ticket visibility, so an unstripped phone photo's embedded GPS data
+ * would otherwise leak a data center/office's physical location even on a
+ * Confidential-visibility ticket.
+ */
+function stripImageMetadata(string $path, string $mimeType): void
+{
+    if (!extension_loaded('gd')) {
+        return;
+    }
+
+    // Guard against a decompression-bomb-style crafted image (small file,
+    // huge decoded pixel buffer) exhausting memory during decode.
+    $dims = @getimagesize($path);
+    if ($dims === false) {
+        return;
+    }
+    [$width, $height] = $dims;
+    if ($width * $height > 40_000_000) { // ~40 MP cap
+        return;
+    }
+
+    $loaders = [
+        'image/jpeg' => 'imagecreatefromjpeg',
+        'image/png'  => 'imagecreatefrompng',
+        'image/gif'  => 'imagecreatefromgif',
+        'image/webp' => 'imagecreatefromwebp',
+    ];
+    $loader = $loaders[$mimeType] ?? null;
+    if ($loader === null || !function_exists($loader)) {
+        return;
+    }
+
+    $image = @$loader($path);
+    if ($image === false) {
+        return;
+    }
+
+    // Preserve transparency for formats that support it.
+    imagesavealpha($image, true);
+    imagealphablending($image, false);
+
+    $tmpPath = $path . '.tmp';
+    $saved = match ($mimeType) {
+        'image/jpeg' => imagejpeg($image, $tmpPath, 90),
+        'image/png'  => imagepng($image, $tmpPath, 6),
+        'image/gif'  => imagegif($image, $tmpPath),
+        'image/webp' => imagewebp($image, $tmpPath, 90),
+        default      => false,
+    };
+    imagedestroy($image);
+
+    if ($saved && file_exists($tmpPath)) {
+        rename($tmpPath, $path);
+    } elseif (file_exists($tmpPath)) {
+        unlink($tmpPath);
+    }
+}
+
 // Check authentication
 if (!isset($_SESSION['user']) || !isset($_SESSION['user']['user_id'])) {
     ResponseHelper::unauthorized();
@@ -184,6 +251,11 @@ if (!move_uploaded_file($file['tmp_name'], $targetPath)) {
     ResponseHelper::serverError('Failed to move uploaded file');
 }
 
+// Strip EXIF/GPS metadata from image uploads before it's ever served back
+if (str_starts_with($mimeType, 'image/')) {
+    stripImageMetadata($targetPath, $mimeType);
+}
+
 // Sanitize original filename
 $originalFilename = basename($file['name']);
 $originalFilename = preg_replace('/[^\w\s\-\.]/', '', $originalFilename);