diff --git a/qt/aqt/addons.py b/qt/aqt/addons.py
index bede5b221..a365b28e3 100644
--- a/qt/aqt/addons.py
+++ b/qt/aqt/addons.py
@@ -149,6 +149,19 @@ class AddonMeta:
         )
 
 
+def package_name_valid(name: str) -> bool:
+    # embedded /?
+    base = os.path.basename(name)
+    if base != name:
+        return False
+    # tries to escape to parent?
+    root = os.getcwd()
+    subfolder = os.path.abspath(os.path.join(root, name))
+    if root.startswith(subfolder):
+        return False
+    return True
+
+
 # fixme: this class should not have any GUI code in it
 class AddonManager:
 
@@ -202,7 +215,7 @@ class AddonManager:
 
     def addonsFolder(self, dir: Optional[str] = None) -> str:
         root = self.mw.pm.addonFolder()
-        if not dir:
+        if dir is None:
             return root
         return os.path.join(root, dir)
 
@@ -381,6 +394,8 @@ class AddonManager:
             if not manifest:
                 return InstallError(errmsg="manifest")
             package = manifest["package"]
+            if not package_name_valid(package):
+                return InstallError(errmsg="invalid package")
             conflicts = manifest.get("conflicts", [])
             found_conflicts = self._disableConflicting(package, conflicts)
             meta = self.addonMeta(package)
diff --git a/qt/tests/test_addons.py b/qt/tests/test_addons.py
index 366ce22ff..f06955878 100644
--- a/qt/tests/test_addons.py
+++ b/qt/tests/test_addons.py
@@ -7,7 +7,7 @@ from zipfile import ZipFile
 
 from mock import MagicMock
 
-from aqt.addons import AddonManager, extract_update_info
+from aqt.addons import AddonManager, extract_update_info, package_name_valid
 
 
 def test_readMinimalManifest():
@@ -94,3 +94,11 @@ def test_update_info():
     r = extract_update_info(20, 1, json_info)
     assert r.current_branch_max_point_ver == -25
     assert r.suitable_branch_last_modified == 333
+
+
+def test_package_name_validation():
+    assert not package_name_valid("")
+    assert not package_name_valid("/")
+    assert not package_name_valid("a/b")
+    assert not package_name_valid("..")
+    assert package_name_valid("ab")