diff --git a/storage/filesystem.go b/storage/filesystem.go
index b8a3e0d..3ad71fd 100644
--- a/storage/filesystem.go
+++ b/storage/filesystem.go
@@ -9,6 +9,7 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"regexp"
 
 	"github.com/emersion/go-vcard"
 	"github.com/emersion/go-webdav/carddav"
@@ -38,7 +39,7 @@ func NewFilesystem(path string) (carddav.Backend, error) {
 func (b *filesystemBackend) pathForContext(ctx context.Context) (string, error) {
 	raw := ctx.Value(auth.AuthCtxKey)
 	if raw == nil {
-		return b.path, nil
+		return "", fmt.Errorf("unauthenticated requests are not supported")
 	}
 	authCtx, ok := raw.(*auth.AuthContext)
 	if !ok {
@@ -57,6 +58,20 @@ func (b *filesystemBackend) pathForContext(ctx context.Context) (string, error)
 	return path, nil
 }
 
+func (b *filesystemBackend) safePath(ctx context.Context, path string) (string, error) {
+	basePath, err := b.pathForContext(ctx)
+	if err != nil {
+		return "", err
+	}
+	// We are mapping to local filesystem path, so be conservative about what to accept
+	// TODO this changes once multiple addess books are supported
+	var valid = regexp.MustCompile(`^/[A-Za-z0-9_-]+(.[a-zA-Z]+)?$`)
+	if !valid.MatchString(path) {
+		return "", fmt.Errorf("invalid request path")
+	}
+	return filepath.Join(basePath, path), nil
+}
+
 func etagForFile(path string) (string, error) {
 	data, err := ioutil.ReadFile(path)
 	if err != nil {
@@ -153,13 +168,12 @@ func (b *filesystemBackend) AddressBook(ctx context.Context) (*carddav.AddressBo
 }
 
 func (b *filesystemBackend) GetAddressObject(ctx context.Context, path string, req *carddav.AddressDataRequest) (*carddav.AddressObject, error) {
-	basePath, err := b.pathForContext(ctx)
+	localPath, err := b.safePath(ctx, path)
 	if err != nil {
 		return nil, err
 	}
-	path = filepath.Join(basePath, path)
 
-	info, err := os.Stat(path)
+	info, err := os.Stat(localPath)
 	if err != nil {
 		return nil, err
 	}
@@ -169,18 +183,18 @@ func (b *filesystemBackend) GetAddressObject(ctx context.Context, path string, r
 		propFilter = req.Props
 	}
 
-	card, err := vcardFromFile(path, propFilter)
+	card, err := vcardFromFile(localPath, propFilter)
 	if err != nil {
 		return nil, err
 	}
 
-	etag, err := etagForFile(path)
+	etag, err := etagForFile(localPath)
 	if err != nil {
 		return nil, err
 	}
 
 	obj := carddav.AddressObject{
-		Path: "/" + filepath.Base(path),
+		Path: path,
 		ModTime: info.ModTime(),
 		ETag: etag,
 		Card: *card,
@@ -249,12 +263,11 @@ func (b *filesystemBackend) QueryAddressObjects(ctx context.Context, query *card
 }
 
 func (b *filesystemBackend) PutAddressObject(ctx context.Context, path string, card vcard.Card) (loc string, err error) {
-	basePath, err := b.pathForContext(ctx)
+	localPath, err := b.safePath(ctx, path)
 	if err != nil {
 		return "", err
 	}
-	internalPath := filepath.Join(basePath, path)
-	f, err := os.OpenFile(internalPath, os.O_RDWR|os.O_CREATE, 0644)
+	f, err := os.OpenFile(localPath, os.O_RDWR|os.O_CREATE, 0644)
 	if err != nil {
 		return "", err
 	}
@@ -270,13 +283,11 @@ func (b *filesystemBackend) PutAddressObject(ctx context.Context, path string, c
 }
 
 func (b *filesystemBackend) DeleteAddressObject(ctx context.Context, path string) error {
-	basePath, err := b.pathForContext(ctx)
+	localPath, err := b.safePath(ctx, path)
 	if err != nil {
 		return err
 	}
-	path = filepath.Join(basePath, path)
-	//TODO does this need more security/sanity checks?
-	err = os.Remove(path)
+	err = os.Remove(localPath)
 	if err != nil {
 		return err
 	}