diff --git a/src/tool_execution.py b/src/tool_execution.py
index a587633c9..8497b157a 100644
--- a/src/tool_execution.py
+++ b/src/tool_execution.py
@@ -71,25 +71,35 @@ _SENSITIVE_FILE_PATTERNS: tuple[str, ...] = (
     "known_hosts",
 )
 
+# Case-folded views used for matching. On a case-insensitive filesystem
+# (Windows, default macOS) ".SSH/AUTHORIZED_KEYS" and ".env" resolve to the
+# same protected files as their lowercase forms, so the deny-list has to fold
+# case before comparing — the sibling resolver already normcases paths for the
+# same reason. casefold (not os.path.normcase) because normcase is a no-op on
+# POSIX, which is exactly where the macOS read-exfil path lives.
+_SENSITIVE_BASENAMES_CF: frozenset[str] = frozenset(b.casefold() for b in _SENSITIVE_BASENAMES)
+_SENSITIVE_FILE_PATTERNS_CF: frozenset[str] = frozenset(p.casefold() for p in _SENSITIVE_FILE_PATTERNS)
+
 
 def _is_sensitive_path(resolved: str) -> bool:
     """Return True if *resolved* falls under a sensitive directory or
     matches a sensitive filename — regardless of what root it sits under.
+
+    Matching is case-insensitive: on Windows / default macOS a case-variant
+    name (``.SSH``, ``AUTHORIZED_KEYS``, ``Id_Rsa``) points at the same file as
+    the lowercase form, so a case-sensitive check would let it slip past the
+    deny-list in every file tool that relies on it.
     """
-    parts = resolved.split(os.sep)
-    filenames: set[str] = {parts[-1]} if parts else set()
+    parts = [p.casefold() for p in resolved.split(os.sep)]
+    filename = parts[-1] if parts else ""
 
     # Check if any path component is a sensitive directory.
     for part in parts:
-        if part in _SENSITIVE_BASENAMES:
+        if part in _SENSITIVE_BASENAMES_CF:
             return True
 
     # Check filename against known sensitive files.
-    for pat in _SENSITIVE_FILE_PATTERNS:
-        if pat in filenames:
-            return True
-
-    return False
+    return filename in _SENSITIVE_FILE_PATTERNS_CF
 
 
 def _tool_path_roots() -> list[str]:
diff --git a/tests/test_tool_path_confinement.py b/tests/test_tool_path_confinement.py
index 6288623c4..f9f1bd03f 100644
--- a/tests/test_tool_path_confinement.py
+++ b/tests/test_tool_path_confinement.py
@@ -57,6 +57,27 @@ def test_non_sensitive_path():
     assert not _is_sensitive_path("/home/user/projects/file.py")
 
 
+def test_sensitive_case_insensitive():
+    """On case-insensitive filesystems (Windows, default macOS) a case-variant
+    name resolves to the same protected file, so the deny-list must match
+    regardless of case. Built with os.path.join so the separator is right on
+    both POSIX and Windows.
+    """
+    from src.tool_execution import _is_sensitive_path
+    # sensitive directory, varied case
+    assert _is_sensitive_path(os.path.join("home", "u", ".SSH", "authorized_keys"))
+    assert _is_sensitive_path(os.path.join("home", "u", ".Gnupg", "pubring.kbx"))
+    # sensitive filename, varied case
+    assert _is_sensitive_path(os.path.join("ws", "AUTHORIZED_KEYS"))
+    assert _is_sensitive_path(os.path.join("ws", "Id_Rsa"))
+    assert _is_sensitive_path(os.path.join("ws", ".ENV"))
+    assert _is_sensitive_path(os.path.join("ws", ".Env"))
+    # both dir and file varied
+    assert _is_sensitive_path(os.path.join("home", "u", ".SSH", "AUTHORIZED_KEYS"))
+    # an ordinary file with none of the sensitive names is still allowed
+    assert not _is_sensitive_path(os.path.join("ws", "Readme.md"))
+
+
 # ── Unit tests on _resolve_tool_path ─────────────────────────────────
 
 def test_blocks_etc_shadow():