diff --git a/src/google/adk/environment/_local_environment.py b/src/google/adk/environment/_local_environment.py
index c58da7f0d99..37ccac93da7 100644
--- a/src/google/adk/environment/_local_environment.py
+++ b/src/google/adk/environment/_local_environment.py
@@ -139,11 +139,30 @@ 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.
+
+    Relative paths are resolved against ``working_dir``.  Absolute paths
+    are accepted only when they stay inside ``working_dir``.
+
+    Args:
+      path: Absolute or working-dir-relative path.
+
+    Returns:
+      The resolved absolute path.
+
+    Raises:
+      RuntimeError: If ``working_dir`` is not set.
+      ValueError: If the resolved path escapes ``working_dir``.
+    """
+    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/src/google/adk/tools/environment/_tools.py b/src/google/adk/tools/environment/_tools.py
index 67baa8f40db..320786f7ef4 100644
--- a/src/google/adk/tools/environment/_tools.py
+++ b/src/google/adk/tools/environment/_tools.py
@@ -45,6 +45,11 @@ def _truncate(text: str, limit: int = MAX_OUTPUT_CHARS) -> str:
   return text[:limit] + f'\n... (truncated, {len(text)} total chars)'
 
 
+def _is_valid_line_number(value: Any) -> bool:
+  """Returns True when *value* is a non-bool integer."""
+  return isinstance(value, int) and not isinstance(value, bool)
+
+
 _EXECUTE_TOOL_DESCRIPTION = """
 Run a shell command in the environment. For running programs, tests, and build
 commands ONLY. WARNING: Do NOT use for file reading -- use the ReadFile tool
@@ -201,23 +206,11 @@ async def run_async(
       return {'status': 'error', 'error': '`path` is required.'}
     start_line = args.get('start_line')
     end_line = args.get('end_line')
-
-    # Use `sed` to read the file if start_line or end_line are specified.
-    if (start_line and start_line > 1) or end_line:
-      start = start_line or 1
-      if end_line:
-        sed_range = f'{start},{end_line}'
-      else:
-        sed_range = f'{start},$'
-      cmd = f"cat -n '{path}' | sed -n '{sed_range}p'"
-      res = await self._environment.execute(cmd)
-      if res.exit_code == 0:
+    for name, value in (('start_line', start_line), ('end_line', end_line)):
+      if value is not None and not _is_valid_line_number(value):
         return {
-            'status': 'ok',
-            'content': _truncate(
-                res.stdout,
-                limit=self._max_output_chars,
-            ),
+            'status': 'error',
+            'error': f'`{name}` must be an integer if provided.',
         }
 
     try:
diff --git a/tests/unittests/tools/test_local_environment.py b/tests/unittests/tools/test_local_environment.py
index 0c1b52d380c..101b9ed1833 100644
--- a/tests/unittests/tools/test_local_environment.py
+++ b/tests/unittests/tools/test_local_environment.py
@@ -81,3 +81,36 @@ async def test_read_nonexistent_raises(self, env: LocalEnvironment):
     """Reading a missing file raises FileNotFoundError."""
     with pytest.raises(FileNotFoundError):
       await env.read_file(Path("does_not_exist.txt"))
+
+  @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)
diff --git a/tests/unittests/tools/test_read_file_tool.py b/tests/unittests/tools/test_read_file_tool.py
new file mode 100644
index 00000000000..c30cea79fa5
--- /dev/null
+++ b/tests/unittests/tools/test_read_file_tool.py
@@ -0,0 +1,153 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Tests for ReadFileTool."""
+
+from pathlib import Path
+from typing import Optional
+
+from google.adk.environment._base_environment import BaseEnvironment
+from google.adk.environment._base_environment import ExecutionResult
+from google.adk.environment._local_environment import LocalEnvironment
+from google.adk.tools.environment._tools import ReadFileTool
+import pytest
+import pytest_asyncio
+
+
+class _StubEnvironment(BaseEnvironment):
+  """Minimal environment double for ReadFileTool tests."""
+
+  def __init__(self, files: dict[str, bytes]):
+    self._files = files
+    self.execute_calls: list[str] = []
+
+  @property
+  def working_dir(self) -> Path:
+    return Path('/tmp/adk-test')
+
+  async def execute(
+      self,
+      command: str,
+      *,
+      timeout: Optional[float] = None,
+  ) -> ExecutionResult:
+    del timeout
+    self.execute_calls.append(command)
+    raise AssertionError('ReadFileTool should not invoke execute().')
+
+  async def read_file(self, path: Path) -> bytes:
+    key = str(path)
+    if key not in self._files:
+      raise FileNotFoundError(key)
+    return self._files[key]
+
+  async def write_file(self, path: Path, content: str | bytes) -> None:
+    del path, content
+    raise NotImplementedError
+
+
+@pytest.mark.asyncio
+async def test_ranged_read_does_not_use_shell():
+  """A ranged read must not shell out (regression: `cat -n | sed` pipeline)."""
+  env = _StubEnvironment({'f.txt': b'l1\nl2\nl3\nl4\n'})
+  tool = ReadFileTool(env)
+
+  result = await tool.run_async(
+      args={'path': 'f.txt', 'start_line': 2, 'end_line': 3},
+      tool_context=None,
+  )
+
+  assert result['status'] == 'ok'
+  assert result['content'] == '     2\tl2\n     3\tl3\n'
+  assert not env.execute_calls
+
+
+@pytest.mark.asyncio
+async def test_shell_metacharacters_in_path_are_literal():
+  """A path with shell metacharacters is treated as a literal filename."""
+  env = _StubEnvironment({'f.txt': b'l1\nl2\n'})
+  tool = ReadFileTool(env)
+
+  result = await tool.run_async(
+      args={'path': "'; id > /tmp/pwned ; echo '", 'start_line': 2},
+      tool_context=None,
+  )
+
+  assert result['status'] == 'error'
+  assert 'File not found' in result['error']
+  assert not env.execute_calls
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize('field', ['start_line', 'end_line'])
+@pytest.mark.parametrize('bad_value', ['2', 2.5, True, None.__class__])
+async def test_non_integer_line_numbers_rejected(field, bad_value):
+  """Non-integer line arguments are rejected instead of reaching a slice.
+
+  Booleans are excluded explicitly: ``isinstance(True, int)`` is True, so a
+  bare int check would let ``True`` through into the slice.
+  """
+  env = _StubEnvironment({'f.txt': b'l1\nl2\n'})
+  tool = ReadFileTool(env)
+
+  result = await tool.run_async(
+      args={'path': 'f.txt', field: bad_value},
+      tool_context=None,
+  )
+
+  assert result['status'] == 'error'
+  assert f'`{field}` must be an integer if provided.' == result['error']
+  assert not env.execute_calls
+
+
+@pytest_asyncio.fixture(name='env')
+async def _env(tmp_path: Path):
+  """Create and initialize a LocalEnvironment backed by a temp directory."""
+  environment = LocalEnvironment(working_dir=tmp_path)
+  await environment.initialize()
+  yield environment
+  await environment.close()
+
+
+@pytest.mark.asyncio
+async def test_shell_injection_payload_creates_no_file(
+    env: LocalEnvironment, tmp_path: Path
+):
+  """End-to-end: an injection payload must not execute against a real env."""
+  canary = tmp_path.parent / 'adk_injection_canary'
+  tool = ReadFileTool(env)
+
+  result = await tool.run_async(
+      args={'path': f"'; touch {canary} ; echo '", 'start_line': 2},
+      tool_context=None,
+  )
+
+  assert result['status'] == 'error'
+  assert not canary.exists()
+
+
+@pytest.mark.asyncio
+async def test_ranged_read_still_works_against_real_env(env: LocalEnvironment):
+  """Ranged reads keep working after the shell path was removed."""
+  await env.write_file('real.txt', 'a\nb\nc\nd\n')
+  tool = ReadFileTool(env)
+
+  result = await tool.run_async(
+      args={'path': 'real.txt', 'start_line': 2, 'end_line': 3},
+      tool_context=None,
+  )
+
+  assert result['status'] == 'ok'
+  assert result['content'] == '     2\tb\n     3\tc\n'
+  assert result['total_lines'] == 4