diff --git a/ci/tools/fetch_ctk_redistrib.py b/ci/tools/fetch_ctk_redistrib.py
index 5007765516e..1bac4ef6bb5 100644
--- a/ci/tools/fetch_ctk_redistrib.py
+++ b/ci/tools/fetch_ctk_redistrib.py
@@ -70,12 +70,25 @@ def load_metadata(*, metadata_path: str | None, metadata_url: str | None) -> dic
         raise ValueError("exactly one of --metadata-path or --metadata-url is required")
 
     if metadata_path is not None:
-        return json.loads(Path(metadata_path).read_text(encoding="utf-8"))
+        return _as_metadata_object(json.loads(Path(metadata_path).read_text(encoding="utf-8")), metadata_path)
 
     assert metadata_url is not None
     metadata_url = validate_metadata_url(metadata_url)
     with urllib.request.urlopen(metadata_url) as response:  # noqa: S310 - scheme is restricted to https above
-        return json.load(response)
+        return _as_metadata_object(json.load(response), metadata_url)
+
+
+def _as_metadata_object(metadata: Any, source: str) -> dict[str, Any]:
+    """Reject JSON that parsed fine but is not a redistrib manifest.
+
+    The manifest is downloaded with ``curl -LSs`` (no ``--fail``), so an error
+    page or a redirect body lands in the file and may still be valid JSON --
+    just not an object. Without this the failure surfaces several frames later
+    as ``TypeError: argument of type 'NoneType' is not iterable``.
+    """
+    if not isinstance(metadata, dict):
+        raise ValueError(f"CTK redistrib metadata from {source} must be a JSON object, got {type(metadata).__name__}")
+    return metadata
 
 
 def resolve_component_name(metadata: dict[str, Any], component: str) -> str:
@@ -101,7 +114,11 @@ def filter_components(
     skipped = []
     for component in filter_static_components(split_components(components), host_platform, cuda_version):
         resolved_component = resolve_component_name(metadata, component)
-        if ctk_subdir in metadata.get(resolved_component, {}):
+        # Guard the type: a top-level key such as "release_label" holds a
+        # string, and ``ctk_subdir in "13.0.0"`` is a substring test rather
+        # than the intended key lookup.
+        component_info = metadata.get(resolved_component)
+        if isinstance(component_info, dict) and ctk_subdir in component_info:
             filtered.append(resolved_component)
         else:
             skipped.append(component)
@@ -114,10 +131,22 @@ def get_component_relative_path(metadata: dict[str, Any], *, host_platform: str,
     component_info = metadata.get(component)
     if component_info is None:
         raise KeyError(f"unknown CTK component {component!r}")
+    if not isinstance(component_info, dict):
+        # Real manifests carry string-valued top-level keys ("release_date",
+        # "release_label", "release_product") alongside the component objects,
+        # so "present" is not the same as "is a component".
+        raise KeyError(
+            f"CTK metadata entry {component!r} is not a component object (got {type(component_info).__name__})"
+        )
 
     subdir_info = component_info.get(ctk_subdir)
     if subdir_info is None:
         raise KeyError(f"CTK component {component!r} is not available for redistrib subdir {ctk_subdir!r}")
+    if not isinstance(subdir_info, dict):
+        raise KeyError(
+            f"CTK component {component!r} entry for redistrib subdir {ctk_subdir!r} "
+            f"is not an object (got {type(subdir_info).__name__})"
+        )
 
     relative_path = subdir_info.get("relative_path")
     if relative_path is None:
diff --git a/ci/tools/tests/test_fetch_ctk_redistrib.py b/ci/tools/tests/test_fetch_ctk_redistrib.py
new file mode 100644
index 00000000000..f821283ca64
--- /dev/null
+++ b/ci/tools/tests/test_fetch_ctk_redistrib.py
@@ -0,0 +1,117 @@
+# SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+# SPDX-License-Identifier: Apache-2.0
+
+from __future__ import annotations
+
+import json
+import os
+import sys
+
+import pytest
+
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), ".."))
+from fetch_ctk_redistrib import main
+
+# Shaped like a real redistrib_*.json: string-valued release keys sit at the
+# top level alongside the component objects.
+METADATA = {
+    "release_date": "2026-01-01",
+    "release_label": "13.0.0",
+    "release_product": "cuda",
+    "cuda_nvcc": {
+        "linux-x86_64": {"relative_path": "cuda_nvcc/linux-x86_64/cuda_nvcc-linux-x86_64.tar.xz"},
+    },
+}
+
+
+def write_metadata(tmp_path, payload):
+    path = tmp_path / "redistrib.json"
+    path.write_text(json.dumps(payload), encoding="utf-8")
+    return str(path)
+
+
+def relpath_argv(metadata_path, component):
+    return [
+        "component-relative-path",
+        "--host-platform",
+        "linux-64",
+        "--component",
+        component,
+        "--metadata-path",
+        metadata_path,
+    ]
+
+
+def filter_argv(metadata_path, components="cuda_nvcc"):
+    return [
+        "filter-components",
+        "--host-platform",
+        "linux-64",
+        "--cuda-version",
+        "13.0.0",
+        "--components",
+        components,
+        "--metadata-path",
+        metadata_path,
+    ]
+
+
+@pytest.mark.agent_authored(model="claude-opus-5")
+def test_valid_component_is_resolved(tmp_path, capsys):
+    assert main(relpath_argv(write_metadata(tmp_path, METADATA), "cuda_nvcc")) == 0
+    assert capsys.readouterr().out.strip() == "cuda_nvcc/linux-x86_64/cuda_nvcc-linux-x86_64.tar.xz"
+
+
+@pytest.mark.agent_authored(model="claude-opus-5")
+@pytest.mark.parametrize("component", ["release_label", "release_date", "release_product"])
+def test_string_valued_top_level_key_is_not_a_component(tmp_path, capsys, component):
+    """`is None` only rejects an absent key, not a wrongly-typed one.
+
+    Every real manifest carries these string-valued keys next to the component
+    objects, so asking for one used to reach `component_info.get(...)` and die
+    with `AttributeError: 'str' object has no attribute 'get'` instead of the
+    tool's own diagnostic.
+    """
+    assert main(relpath_argv(write_metadata(tmp_path, METADATA), component)) == 1
+    assert "ERROR:" in capsys.readouterr().err
+
+
+@pytest.mark.agent_authored(model="claude-opus-5")
+def test_absent_component_still_reports_cleanly(tmp_path, capsys):
+    assert main(relpath_argv(write_metadata(tmp_path, METADATA), "not_a_component")) == 1
+    assert "unknown CTK component" in capsys.readouterr().err
+
+
+@pytest.mark.agent_authored(model="claude-opus-5")
+def test_non_object_subdir_entry_is_reported(tmp_path, capsys):
+    metadata = {"cuda_nvcc": {"linux-x86_64": "cuda_nvcc/linux-x86_64/x.tar.xz"}}
+    assert main(relpath_argv(write_metadata(tmp_path, metadata), "cuda_nvcc")) == 1
+    assert "ERROR:" in capsys.readouterr().err
+
+
+@pytest.mark.agent_authored(model="claude-opus-5")
+@pytest.mark.parametrize(
+    "payload",
+    [
+        pytest.param(None, id="null"),
+        pytest.param([1, 2], id="array"),
+        pytest.param("13.0.0", id="string"),
+    ],
+)
+@pytest.mark.parametrize("argv_builder", [relpath_argv, filter_argv], ids=["relative-path", "filter"])
+def test_metadata_that_is_not_an_object_is_reported(tmp_path, capsys, payload, argv_builder):
+    """The manifest is downloaded with `curl -LSs` (no --fail), so an error
+    page or redirect body can parse as valid JSON that is not an object."""
+    path = write_metadata(tmp_path, payload)
+    argv = argv_builder(path, "cuda_nvcc") if argv_builder is relpath_argv else argv_builder(path)
+
+    assert main(argv) == 1
+    assert "must be a JSON object" in capsys.readouterr().err
+
+
+@pytest.mark.agent_authored(model="claude-opus-5")
+def test_filter_skips_a_string_valued_top_level_key(tmp_path, capsys):
+    assert main(filter_argv(write_metadata(tmp_path, METADATA), "release_label")) == 0
+    captured = capsys.readouterr()
+    assert captured.out.strip() == ""
+    assert "Skipping unsupported CTK component 'release_label'" in captured.err