diff --git a/MODULE.md b/MODULE.md
index 6e1064c4..32c86bcf 100644
--- a/MODULE.md
+++ b/MODULE.md
@@ -48,7 +48,9 @@ checks. Check is an internal trusted-host operation, not a model-visible tool.
 Path checks require the host's absolute operation-resolved target, resolve existing
 ancestors including symlinks, and enforce the
 credential/system/traversal floor on lexical and resolved forms even when
-policy is disabled. Unknown native path dialects, broken symlinks and failed
+policy is disabled. Traversal is any segment that starts with `..` and holds only dots and
+spaces (`..`, `.. `, `...`), on every OS, since Windows normalizes those to `..`; such a
+`forbidden_paths` entry is rejected at registration. Unknown native path dialects, broken symlinks and failed
 resolution deny. Enabled action roots must resolve to existing directories;
 workspace and configured forbidden roots deny before approval. New files can
 be checked through their existing parent. Permission does not guarantee
@@ -503,7 +505,8 @@ cannot bind the call answers an error, never an allow. Latency budgets are per c
   like `CheckPath`.
 - `ProtectedPath2` (`ProtectedPathRequest2` -> `ProtectedPathResponse2`): the unconditional
   lexical floor with no scope and no filesystem access: credential stores, system and
-  installation roots, `..` traversal, NUL bytes and Windows roots and extended prefixes, on every
+  installation roots, parent-directory traversal (`..` and any segment of two or more dots
+  followed only by dots and spaces, such as `.. ` or `...`, which Windows normalizes to `..`), NUL bytes and Windows roots and extended prefixes, on every
   OS. At most 4096 paths. Budget: in memory, sub-millisecond.
 - `ProtectedFloor2` (no arguments): the floor's vocabulary (credential directories, single-file
   stores, segment pairs, lower-cased absolute prefixes), built from the constants the matcher
diff --git a/crates/tinysecurity-bus/src/path_batch.rs b/crates/tinysecurity-bus/src/path_batch.rs
index 92991b32..a7786ccd 100644
--- a/crates/tinysecurity-bus/src/path_batch.rs
+++ b/crates/tinysecurity-bus/src/path_batch.rs
@@ -61,7 +61,8 @@ pub struct PathBatchResponse2 {
 /// Query the unconditional protected-path floor for paths outside any scope.
 ///
 /// The floor is lexical and needs no registered policy: credential stores, core
-/// system roots, `..` traversal and NUL bytes. It holds whether or not the host's
+/// system roots, parent-directory traversal (`..` and the forms Windows normalizes to it,
+/// such as `.. ` and `...`) and NUL bytes. It holds whether or not the host's
 /// discretionary policy is enabled.
 #[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
 #[serde(deny_unknown_fields)]
diff --git a/crates/tinysecurity-policy/src/floor_tests.rs b/crates/tinysecurity-policy/src/floor_tests.rs
index 71280c8e..ca0714b5 100644
--- a/crates/tinysecurity-policy/src/floor_tests.rs
+++ b/crates/tinysecurity-policy/src/floor_tests.rs
@@ -109,3 +109,27 @@ fn file_store_subset_stays_within_credential_components() {
         assert!(CREDENTIAL_COMPONENTS.contains(name), "{name}");
     }
 }
+
+#[test]
+fn windows_normalized_parent_segments_count_as_traversal() {
+    for path in [
+        r"C:\safe\.. \Windows\System32",
+        r"C:\safe\..\Windows",
+        r"C:\safe\... \x",
+        r"C:\safe\.. . \x",
+        "/work/.. /etc/passwd",
+        "/work/.../x",
+    ] {
+        assert!(floor(path), "{path:?}");
+        assert!(crate::protected_path(&PathBuf::from(path)), "{path:?}");
+    }
+    // Ordinary names that merely contain dots stay usable.
+    for path in [
+        "/work/my..file.txt",
+        "/work/.hidden",
+        "/work/a. b",
+        "/work/.config.d",
+    ] {
+        assert!(!floor(path), "{path:?}");
+    }
+}
diff --git a/crates/tinysecurity-policy/src/path.rs b/crates/tinysecurity-policy/src/path.rs
index e0979188..f2094f9a 100644
--- a/crates/tinysecurity-policy/src/path.rs
+++ b/crates/tinysecurity-policy/src/path.rs
@@ -46,6 +46,11 @@ pub(super) const WINDOWS_SYSTEM_ROOTS: &[&str] = &[
     "program files (x86)",
     "programdata",
 ];
+/// A parent-directory segment, including the forms Windows normalizes to `..`
+/// (trailing spaces and dots, as in `.. ` or `...`). Checked lexically on every OS.
+pub(super) fn parent_segment(segment: &str) -> bool {
+    segment.starts_with("..") && segment.trim_end_matches([' ', '.']).is_empty()
+}
 pub(super) fn denial_segment(segment: &str) -> &str {
     segment
         .split(':')
@@ -61,7 +66,10 @@ pub(super) fn floor(path: &str) -> bool {
     let segments: Vec<_> = normalized.split('/').filter(|s| !s.is_empty()).collect();
     // Both slash dialects are checked on every OS. The additional macOS
     // /private aliases are protected before canonicalization too.
-    if path.contains('\0') || segments.contains(&"..") || credential_store(&segments) {
+    if path.contains('\0')
+        || segments.iter().any(|segment| parent_segment(segment))
+        || credential_store(&segments)
+    {
         return true;
     }
     CRITICAL_ROOTS
diff --git a/crates/tinysecurity-policy/src/path_scope.rs b/crates/tinysecurity-policy/src/path_scope.rs
index 1edf456c..244246cd 100644
--- a/crates/tinysecurity-policy/src/path_scope.rs
+++ b/crates/tinysecurity-policy/src/path_scope.rs
@@ -35,7 +35,9 @@ pub fn protected_path(path: &Path) -> bool {
     if normalized.contains('\0')
         || normalized.contains("..%2f")
         || normalized.contains("%2f..")
-        || segments.contains(&"..")
+        || segments
+            .iter()
+            .any(|segment| crate::path::parent_segment(segment))
         || crate::path::credential_store(&segments)
     {
         return true;
diff --git a/crates/tinysecurity-policy/src/scoped_forbidden.rs b/crates/tinysecurity-policy/src/scoped_forbidden.rs
index 43effeb6..24a9563c 100644
--- a/crates/tinysecurity-policy/src/scoped_forbidden.rs
+++ b/crates/tinysecurity-policy/src/scoped_forbidden.rs
@@ -30,7 +30,7 @@ fn expand_home(entry: &str, home: Option<&Path>) -> Option<Result<PathBuf>> {
 }
 
 fn traverses(entry: &str) -> bool {
-    entry.contains('\0') || entry.split(['/', '\\']).any(|part| part == "..")
+    entry.contains('\0') || entry.split(['/', '\\']).any(crate::path::parent_segment)
 }
 
 fn resolve_entry(entry: &str, action_dir: &Path, home: Option<&Path>) -> Result<PathBuf> {
diff --git a/crates/tinysecurity-policy/src/scoped_forbidden_tests.rs b/crates/tinysecurity-policy/src/scoped_forbidden_tests.rs
index 15d28308..0f0e6b3f 100644
--- a/crates/tinysecurity-policy/src/scoped_forbidden_tests.rs
+++ b/crates/tinysecurity-policy/src/scoped_forbidden_tests.rs
@@ -110,3 +110,15 @@ fn entries_inside_the_unconditional_floor_are_redundant_noops() {
         Ok(vec![kept])
     );
 }
+
+#[test]
+fn windows_normalized_traversal_entries_are_rejected_not_dropped() {
+    let home = abs("home");
+    for entry in ["a/.. /b", "a\\.. \\b", "/abs/.../x", "~/.. ./x"] {
+        assert_eq!(
+            effective(&[entry], Some(&home)),
+            Err(Error::InvalidArguments),
+            "{entry:?}"
+        );
+    }
+}