diff --git a/server/internal/handler/file.go b/server/internal/handler/file.go
index ab7882ee..096e9a13 100644
--- a/server/internal/handler/file.go
+++ b/server/internal/handler/file.go
@@ -59,11 +59,23 @@ func (h *Handler) UploadFile(w http.ResponseWriter, r *http.Request) {
 	}
 	defer file.Close()
 
-	contentType := header.Header.Get("Content-Type")
+	// Sniff actual content type from file bytes instead of trusting the client header.
+	buf := make([]byte, 512)
+	n, err := file.Read(buf)
+	if err != nil && err != io.EOF {
+		writeError(w, http.StatusBadRequest, "failed to read file")
+		return
+	}
+	contentType := http.DetectContentType(buf[:n])
 	if !isContentTypeAllowed(contentType) {
 		writeError(w, http.StatusBadRequest, fmt.Sprintf("file type not allowed: %s", contentType))
 		return
 	}
+	// Seek back so the full file is uploaded.
+	if _, err := file.Seek(0, io.SeekStart); err != nil {
+		writeError(w, http.StatusInternalServerError, "failed to read file")
+		return
+	}
 
 	data, err := io.ReadAll(file)
 	if err != nil {
@@ -77,7 +89,7 @@ func (h *Handler) UploadFile(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusInternalServerError, "internal error")
 		return
 	}
-	key := hex.EncodeToString(b) + path.Ext(header.Filename)
+	key := "uploads/" + hex.EncodeToString(b) + path.Ext(header.Filename)
 
 	link, err := h.Storage.Upload(r.Context(), key, data, contentType, header.Filename)
 	if err != nil {
diff --git a/server/internal/storage/s3.go b/server/internal/storage/s3.go
index 3f03ea86..b29375f0 100644
--- a/server/internal/storage/s3.go
+++ b/server/internal/storage/s3.go
@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"log/slog"
 	"os"
+	"strings"
 
 	"github.com/aws/aws-sdk-go-v2/aws"
 	"github.com/aws/aws-sdk-go-v2/config"
@@ -73,7 +74,7 @@ func (s *S3Storage) Upload(ctx context.Context, key string, data []byte, content
 		Key:                aws.String(key),
 		Body:               bytes.NewReader(data),
 		ContentType:        aws.String(contentType),
-		ContentDisposition: aws.String(fmt.Sprintf(`inline; filename="%s"`, filename)),
+		ContentDisposition: aws.String(fmt.Sprintf(`inline; filename="%s"`, strings.ReplaceAll(filename, `"`, "'"))),
 		CacheControl:       aws.String("max-age=432000,public"),
 		StorageClass:       types.StorageClassIntelligentTiering,
 	})