From 4da4bf69ca404132763bb5142e084191f91153b6 Mon Sep 17 00:00:00 2001
From: kolaente <k@knt.li>
Date: Tue, 15 Jul 2025 13:21:48 +0200
Subject: [PATCH] fix(background): validate unsupported formats and show error
 message (#1123)

---
 pkg/modules/background/handler/background.go | 27 +++++++++++++
 pkg/modules/background/handler/errors.go     | 42 ++++++++++++++++++++
 2 files changed, 69 insertions(+)
 create mode 100644 pkg/modules/background/handler/errors.go

diff --git a/pkg/modules/background/handler/background.go b/pkg/modules/background/handler/background.go
index acf3cbf88..c89253474 100644
--- a/pkg/modules/background/handler/background.go
+++ b/pkg/modules/background/handler/background.go
@@ -52,6 +52,15 @@ import (
 	"xorm.io/xorm"
 )
 
+var allowedImageMimes = []string{
+	"image/jpeg",
+	"image/png",
+	"image/gif",
+	"image/bmp",
+	"image/tiff",
+	"image/webp",
+}
+
 // BackgroundProvider represents a thing which holds a background provider
 // Lets us get a new fresh provider every time we need one.
 type BackgroundProvider struct {
@@ -202,6 +211,17 @@ func (bp *BackgroundProvider) UploadBackground(c echo.Context) error {
 		_ = s.Rollback()
 		return c.JSON(http.StatusBadRequest, models.Message{Message: "Uploaded file is no image."})
 	}
+	supported := false
+	for _, m := range allowedImageMimes {
+		if mime.Is(m) {
+			supported = true
+			break
+		}
+	}
+	if !supported {
+		_ = s.Rollback()
+		return c.JSON(http.StatusBadRequest, models.Message{Message: "Unsupported image format. Allowed: " + strings.Join(allowedImageMimes, ",")})
+	}
 
 	err = SaveBackgroundFile(s, auth, project, srcf, file.Filename, uint64(file.Size))
 	if err != nil {
@@ -209,6 +229,9 @@ func (bp *BackgroundProvider) UploadBackground(c echo.Context) error {
 		if files.IsErrFileIsTooLarge(err) {
 			return echo.ErrBadRequest
 		}
+		if IsErrFileUnsupportedImageFormat(err) {
+			return c.JSON(http.StatusBadRequest, models.Message{Message: "Unsupported image format. Allowed: " + strings.Join(allowedImageMimes, ",")})
+		}
 
 		return handler.HandleHTTPError(err)
 	}
@@ -228,9 +251,13 @@ func (bp *BackgroundProvider) UploadBackground(c echo.Context) error {
 }
 
 func SaveBackgroundFile(s *xorm.Session, auth web.Auth, project *models.Project, srcf io.ReadSeeker, filename string, filesize uint64) (err error) {
+	mime, _ := mimetype.DetectReader(srcf)
 	_, _ = srcf.Seek(0, io.SeekStart)
 	src, err := imaging.Decode(srcf)
 	if err != nil {
+		if strings.Contains(err.Error(), "unknown format") {
+			return ErrFileUnsupportedImageFormat{Mime: mime.String()}
+		}
 		return err
 	}
 
diff --git a/pkg/modules/background/handler/errors.go b/pkg/modules/background/handler/errors.go
new file mode 100644
index 000000000..beaf46657
--- /dev/null
+++ b/pkg/modules/background/handler/errors.go
@@ -0,0 +1,42 @@
+// Vikunja is a to-do list application to facilitate your life.
+// Copyright 2018-present Vikunja and contributors. All rights reserved.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package handler
+
+import (
+	"errors"
+	"fmt"
+)
+
+// ErrFileUnsupportedImageFormat defines an error where an uploaded image format is not supported
+// by the imaging library
+//
+// This is returned when decoding the image fails because the format is unknown.
+type ErrFileUnsupportedImageFormat struct {
+	Mime string
+}
+
+// Error is the error implementation of ErrFileUnsupportedImageFormat
+func (err ErrFileUnsupportedImageFormat) Error() string {
+	return fmt.Sprintf("file is not a supported image format [Mime: %s]", err.Mime)
+}
+
+// IsErrFileUnsupportedImageFormat checks if an error is ErrFileUnsupportedImageFormat
+func IsErrFileUnsupportedImageFormat(err error) bool {
+	var errFileUnsupportedImageFormat ErrFileUnsupportedImageFormat
+	ok := errors.As(err, &errFileUnsupportedImageFormat)
+	return ok
+}