diff --git a/src/google/adk/environment/_local_environment.py b/src/google/adk/environment/_local_environment.py
index c58da7f0d9..4695ef6f52 100644
--- a/src/google/adk/environment/_local_environment.py
+++ b/src/google/adk/environment/_local_environment.py
@@ -139,11 +139,16 @@ async def write_file(self, path: str | Path, content: str | bytes) -> None:
     return await asyncio.to_thread(self._sync_write, resolved, content)
 
   def _resolve_path(self, path: str | Path) -> str:
-    """Resolve a relative path against the working directory."""
-    path = str(path)
-    if os.path.isabs(path):
-      return path
-    return os.path.join(self._working_dir, path)
+    """Resolve a file path inside the working directory."""
+    candidate = Path(path)
+    working_dir = self.working_dir.resolve()
+    if not candidate.is_absolute():
+      candidate = working_dir / candidate
+
+    resolved = candidate.resolve()
+    if not resolved.is_relative_to(working_dir):
+      raise ValueError(f'Path escapes working directory: {path}')
+    return str(resolved)
 
   @staticmethod
   def _sync_read(path: str) -> bytes:
diff --git a/tests/unittests/tools/test_local_environment.py b/tests/unittests/tools/test_local_environment.py
index 0c1b52d380..4f1367b72a 100644
--- a/tests/unittests/tools/test_local_environment.py
+++ b/tests/unittests/tools/test_local_environment.py
@@ -76,6 +76,39 @@ async def test_write_creates_parent_dirs(self, env: LocalEnvironment):
     data = await env.read_file("sub/dir/file.txt")
     assert data == b"nested"
 
+  @pytest.mark.asyncio
+  async def test_absolute_path_inside_working_dir(self, env: LocalEnvironment):
+    """Absolute paths are accepted when they stay inside the workspace."""
+    path = env.working_dir / "absolute.txt"
+    await env.write_file(path, "absolute")
+    data = await env.read_file(path)
+    assert data == b"absolute"
+
+  @pytest.mark.asyncio
+  async def test_rejects_relative_path_escape(self, env: LocalEnvironment):
+    """Parent traversal cannot escape the workspace."""
+    outside = env.working_dir.parent / "outside.txt"
+    outside.write_text("secret", encoding="utf-8")
+
+    with pytest.raises(ValueError, match="escapes working directory"):
+      await env.read_file(Path("..") / outside.name)
+
+    with pytest.raises(ValueError, match="escapes working directory"):
+      await env.write_file(Path("..") / "write-outside.txt", "nope")
+
+    assert not (env.working_dir.parent / "write-outside.txt").exists()
+
+  @pytest.mark.asyncio
+  async def test_rejects_absolute_path_outside_working_dir(
+      self, env: LocalEnvironment
+  ):
+    """Absolute paths outside the workspace are rejected."""
+    outside = env.working_dir.parent / "outside-absolute.txt"
+    outside.write_text("secret", encoding="utf-8")
+
+    with pytest.raises(ValueError, match="escapes working directory"):
+      await env.read_file(outside)
+
   @pytest.mark.asyncio
   async def test_read_nonexistent_raises(self, env: LocalEnvironment):
     """Reading a missing file raises FileNotFoundError."""