CI and Context

.github/workflows/ci.yml

@@ -26,7 +26,9 @@ jobs:
     - name: Set up Go 1.x
       uses: actions/setup-go@v4
       with:
-        go-version: ${{ matrix.go_version }}
+        go-version-file: './go.mod'
+        check-latest: true
+    - run: go version
 
     - name: Test
       run: go test -v ./...

context/context.go

@@ -2380,6 +2380,15 @@ func (ctx *Context) FormFiles(key string, before ...func(*Context, *multipart.Fi
 	return nil, nil, http.ErrMissingFile
 }
 
+var (
+	// ValidFileNameRegexp is used to validate the user input by using a regular expression.
+	// See `Context.UploadFormFiles` method.
+	ValidFilenameRegexp = regexp.MustCompile(`^[a-zA-Z0-9_\-\.]+$`)
+	// ValidExtensionRegexp acts as an allowlist of valid extensions. It's optional. Defaults to nil (all file extensions are allowed to be uploaded).
+	// See `Context.UploadFormFiles` method.
+	ValidExtensionRegexp *regexp.Regexp
+)
+
 // UploadFormFiles uploads any received file(s) from the client
 // to the system physical location "destDirectory".
 //
@@ -2418,24 +2427,35 @@ func (ctx *Context) UploadFormFiles(destDirectory string, before ...func(*Contex
 			for _, files := range fhs {
 			innerLoop:
 				for _, file := range files {
-					// Security fix for go < 1.17.5:
-					// Reported by Kirill Efimov (snyk.io) through security reports.
-					file.Filename = filepath.Base(file.Filename)
-
 					for _, b := range before {
 						if !b(ctx, file) {
 							continue innerLoop
 						}
 					}
 
+					// Security fix for go < 1.17.5:
+					// Reported by Kirill Efimov (snyk.io) through security reports.
+					filename := filepath.Base(filepath.ToSlash(file.Filename))
+
 					// CWE-99.
-					// Sanitize the user input by removing any path separators.
-					sanitizedInput := strings.ReplaceAll(file.Filename, string(os.PathSeparator), "")
+
+					// Sanitize the user input by using a regular expression
+					// and an allowlist of valid extensions
+					isValidFilename := ValidFilenameRegexp.MatchString(filename)
+					if !isValidFilename {
+						// Reject the input as it is invalid or unsafe.
+						continue innerLoop
+					}
+
+					if ValidExtensionRegexp != nil && !ValidExtensionRegexp.MatchString(filename) {
+						// Reject the input as it is invalid or unsafe.
+						continue innerLoop
+					}
 
 					// Join the sanitized input with the destination directory.
-					destPath := filepath.Join(destDirectory, sanitizedInput)
+					destPath := filepath.Join(destDirectory, filename)
 
-					// Get the canonical path of the destination.
+					// Get the canonical path of the destination
 					canonicalDestPath, err := filepath.EvalSymlinks(destPath)
 					if err != nil {
 						return nil, 0, err