diff --git a/handlers.go b/handlers.go
index e02d63f..d56b966 100644
--- a/handlers.go
+++ b/handlers.go
@@ -2,12 +2,14 @@ package restserver
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
 	"log"
 	"net/http"
 	"os"
+	"path"
 	"path/filepath"
 	"strings"
 	"time"
@@ -20,12 +22,83 @@ func isHashed(dir string) bool {
 	return dir == "data"
 }
 
-func getRepo(r *http.Request) string {
-	if strings.HasPrefix(fmt.Sprintf("%s", middleware.Pattern(r.Context())), "/:repo") {
-		return filepath.Join(Config.Path, pat.Param(r, "repo"))
+func valid(name string) bool {
+	// taken from net/http.Dir
+	if strings.Contains(name, "\x00") {
+		return false
 	}
 
-	return Config.Path
+	if filepath.Separator != '/' && strings.ContainsRune(name, filepath.Separator) {
+		return false
+	}
+
+	return true
+}
+
+var validTypes = []string{"data", "index", "keys", "locks", "snapshots", "config"}
+
+func isValidType(name string) bool {
+	for _, tpe := range validTypes {
+		if name == tpe {
+			return true
+		}
+	}
+
+	return false
+}
+
+// join takes a number of path names, sanitizes them, and returns them joined
+// with base for the current operating system to use (dirs separated by
+// filepath.Separator). The returned path is always either equal to base or a
+// subdir of base.
+func join(base string, names ...string) (string, error) {
+	clean := make([]string, 0, len(names)+1)
+	clean = append(clean, base)
+
+	// taken from net/http.Dir
+	for _, name := range names {
+		if !valid(name) {
+			return "", errors.New("invalid character in path")
+		}
+
+		clean = append(clean, filepath.FromSlash(path.Clean("/"+name)))
+	}
+
+	return filepath.Join(clean...), nil
+}
+
+// getRepo returns the repository location, relative to Config.Path.
+func getRepo(r *http.Request) string {
+	if strings.HasPrefix(fmt.Sprintf("%s", middleware.Pattern(r.Context())), "/:repo") {
+		return pat.Param(r, "repo")
+	}
+
+	return "."
+}
+
+// getPath returns the path for a file type in the repo.
+func getPath(r *http.Request, fileType string) (string, error) {
+	if !isValidType(fileType) {
+		return "", errors.New("invalid file type")
+	}
+	return join(Config.Path, getRepo(r), fileType)
+}
+
+// getFilePath returns the path for a file in the repo.
+func getFilePath(r *http.Request, fileType, name string) (string, error) {
+	if !isValidType(fileType) {
+		return "", errors.New("invalid file type")
+	}
+
+	if isHashed(fileType) {
+		if len(name) < 2 {
+			return "", errors.New("file name is too short")
+		}
+
+		return join(Config.Path, getRepo(r), fileType, name[:2], name)
+	}
+
+	return join(Config.Path, getRepo(r), fileType, name)
 }
 
 // AuthHandler wraps h with a http.HandlerFunc that performs basic authentication against the user/passwords pairs
@@ -46,7 +119,12 @@ func CheckConfig(w http.ResponseWriter, r *http.Request) {
 	if Config.Debug {
 		log.Println("CheckConfig()")
 	}
-	cfg := filepath.Join(getRepo(r), "config")
+	cfg, err := getPath(r, "config")
+	if err != nil {
+		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
+		return
+	}
+
 	st, err := os.Stat(cfg)
 	if err != nil {
 		if Config.Debug {
@@ -64,7 +142,11 @@ func GetConfig(w http.ResponseWriter, r *http.Request) {
 	if Config.Debug {
 		log.Println("GetConfig()")
 	}
-	cfg := filepath.Join(getRepo(r), "config")
+	cfg, err := getPath(r, "config")
+	if err != nil {
+		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
+		return
+	}
 
 	bytes, err := ioutil.ReadFile(cfg)
 	if err != nil {
@@ -83,7 +165,11 @@ func SaveConfig(w http.ResponseWriter, r *http.Request) {
 	if Config.Debug {
 		log.Println("SaveConfig()")
 	}
-	cfg := filepath.Join(getRepo(r), "config")
+	cfg, err := getPath(r, "config")
+	if err != nil {
+		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
+		return
+	}
 
 	bytes, err := ioutil.ReadAll(r.Body)
 	if err != nil {
@@ -108,8 +194,13 @@ func DeleteConfig(w http.ResponseWriter, r *http.Request) {
 	if Config.Debug {
 		log.Println("DeleteConfig()")
 	}
+	cfg, err := getPath(r, "config")
+	if err != nil {
+		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
+		return
+	}
 
-	if err := os.Remove(filepath.Join(getRepo(r), "config")); err != nil {
+	if err := os.Remove(cfg); err != nil {
 		if Config.Debug {
 			log.Print(err)
 		}
@@ -127,8 +218,12 @@ func ListBlobs(w http.ResponseWriter, r *http.Request) {
 	if Config.Debug {
 		log.Println("ListBlobs()")
 	}
-	dir := pat.Param(r, "type")
-	path := filepath.Join(getRepo(r), dir)
+	fileType := pat.Param(r, "type")
+	path, err := getPath(r, fileType)
+	if err != nil {
+		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
+		return
+	}
 
 	items, err := ioutil.ReadDir(path)
 	if err != nil {
@@ -141,7 +236,7 @@ func ListBlobs(w http.ResponseWriter, r *http.Request) {
 
 	var names []string
 	for _, i := range items {
-		if isHashed(dir) {
+		if isHashed(fileType) {
 			subpath := filepath.Join(path, i.Name())
 			subitems, err := ioutil.ReadDir(subpath)
 			if err != nil {
@@ -176,13 +271,12 @@ func CheckBlob(w http.ResponseWriter, r *http.Request) {
 	if Config.Debug {
 		log.Println("CheckBlob()")
 	}
-	dir := pat.Param(r, "type")
-	name := pat.Param(r, "name")
 
-	if isHashed(dir) {
-		name = filepath.Join(name[:2], name)
+	path, err := getFilePath(r, pat.Param(r, "type"), pat.Param(r, "name"))
+	if err != nil {
+		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
+		return
 	}
-	path := filepath.Join(getRepo(r), dir, name)
 
 	st, err := os.Stat(path)
 	if err != nil {
@@ -201,13 +295,12 @@ func GetBlob(w http.ResponseWriter, r *http.Request) {
 	if Config.Debug {
 		log.Println("GetBlob()")
 	}
-	dir := pat.Param(r, "type")
-	name := pat.Param(r, "name")
 
-	if isHashed(dir) {
-		name = filepath.Join(name[:2], name)
+	path, err := getFilePath(r, pat.Param(r, "type"), pat.Param(r, "name"))
+	if err != nil {
+		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
+		return
 	}
-	path := filepath.Join(getRepo(r), dir, name)
 
 	file, err := os.Open(path)
 	if err != nil {
@@ -227,14 +320,12 @@ func SaveBlob(w http.ResponseWriter, r *http.Request) {
 	if Config.Debug {
 		log.Println("SaveBlob()")
 	}
-	repo := getRepo(r)
-	dir := pat.Param(r, "type")
-	name := pat.Param(r, "name")
 
-	if isHashed(dir) {
-		name = filepath.Join(name[:2], name)
+	path, err := getFilePath(r, pat.Param(r, "type"), pat.Param(r, "name"))
+	if err != nil {
+		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
+		return
 	}
-	path := filepath.Join(repo, dir, name)
 
 	tf, err := os.OpenFile(path, os.O_CREATE|os.O_WRONLY|os.O_EXCL, 0600)
 	if err != nil {
@@ -280,13 +371,12 @@ func DeleteBlob(w http.ResponseWriter, r *http.Request) {
 	if Config.Debug {
 		log.Println("DeleteBlob()")
 	}
-	dir := pat.Param(r, "type")
-	name := pat.Param(r, "name")
 
-	if isHashed(dir) {
-		name = filepath.Join(name[:2], name)
+	path, err := getFilePath(r, pat.Param(r, "type"), pat.Param(r, "name"))
+	if err != nil {
+		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
+		return
 	}
-	path := filepath.Join(getRepo(r), dir, name)
 
 	if err := os.Remove(path); err != nil {
 		if Config.Debug {
@@ -306,7 +396,12 @@ func CreateRepo(w http.ResponseWriter, r *http.Request) {
 	if Config.Debug {
 		log.Println("CreateRepo()")
 	}
-	repo := getRepo(r)
+
+	repo, err := join(Config.Path, getRepo(r))
+	if err != nil {
+		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
+		return
+	}
 
 	if r.URL.Query().Get("create") != "true" {
 		http.Error(w, http.StatusText(http.StatusBadRequest), http.StatusBadRequest)
@@ -321,7 +416,11 @@ func CreateRepo(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	for _, d := range []string{"data", "index", "keys", "locks", "snapshots", "tmp"} {
+	for _, d := range validTypes {
+		if d == "config" {
+			continue
+		}
+
 		if err := os.MkdirAll(filepath.Join(repo, d), 0700); err != nil {
 			log.Print(err)
 			http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
diff --git a/handlers_test.go b/handlers_test.go
new file mode 100644
index 0000000..6536a26
--- /dev/null
+++ b/handlers_test.go
@@ -0,0 +1,39 @@
+package restserver
+
+import (
+	"path/filepath"
+	"testing"
+)
+
+func TestJoin(t *testing.T) {
+	var tests = []struct {
+		base, name string
+		result     string
+	}{
+		{"/", "foo/bar", "/foo/bar"},
+		{"/srv/server", "foo/bar", "/srv/server/foo/bar"},
+		{"/srv/server", "/foo/bar", "/srv/server/foo/bar"},
+		{"/srv/server", "foo/../bar", "/srv/server/bar"},
+		{"/srv/server", "../bar", "/srv/server/bar"},
+		{"/srv/server", "..", "/srv/server"},
+		{"/srv/server", "../..", "/srv/server"},
+		{"/srv/server", "/repo/data/", "/srv/server/repo/data"},
+		{"/srv/server", "/repo/data/../..", "/srv/server"},
+		{"/srv/server", "/repo/data/../data/../../..", "/srv/server"},
+		{"/srv/server", "/repo/data/../data/../../..", "/srv/server"},
+	}
+
+	for _, test := range tests {
+		t.Run("", func(t *testing.T) {
+			got, err := join(filepath.FromSlash(test.base), test.name)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			want := filepath.FromSlash(test.result)
+			if got != want {
+				t.Fatalf("wrong result returned, want %v, got %v", want, got)
+			}
+		})
+	}
+}