diff --git a/src/specify_cli/extensions/__init__.py b/src/specify_cli/extensions/__init__.py
index 8dd1b10554..e8d90ecf3a 100644
--- a/src/specify_cli/extensions/__init__.py
+++ b/src/specify_cli/extensions/__init__.py
@@ -49,6 +49,28 @@
     }
 )
 EXTENSION_COMMAND_NAME_PATTERN = re.compile(r"^speckit\.([a-z0-9-]+)\.([a-z0-9-]+)$")
+EXTENSION_ID_PATTERN = re.compile(r"^[a-z0-9-]+$")
+
+# Characters allowed verbatim in a catalog-provided version when it is used to
+# build a download filename. Anything else (path separators, "..", control
+# chars, whitespace) is collapsed to "-" so an untrusted version cannot inject
+# a nested path or an unwritable filename — we sanitize rather than rely on the
+# post-hoc Path.resolve() containment check as the primary guard.
+_UNSAFE_VERSION_TOKEN_PATTERN = re.compile(r"[^A-Za-z0-9._-]+")
+
+
+def _safe_version_token(version: Any, fallback: str = "unknown") -> str:
+    """Reduce a catalog ``version`` to a filename-safe token.
+
+    Non-strings (JSON null, numbers) and blank values degrade to ``fallback``.
+    Path separators and traversal tokens are stripped so the result can never
+    span directories or escape the download target.
+    """
+    if not isinstance(version, str):
+        return fallback
+    token = _UNSAFE_VERSION_TOKEN_PATTERN.sub("-", version).strip("-.")
+    return token or fallback
+
 
 VALID_EFFECTS = frozenset({"read-only", "read-write"})
 
@@ -217,7 +239,7 @@ def _validate(self):
                 raise ValidationError(f"Missing extension.{field}")
 
         # Validate extension ID format
-        if not re.match(r"^[a-z0-9-]+$", ext["id"]):
+        if not EXTENSION_ID_PATTERN.match(ext["id"]):
             raise ValidationError(
                 f"Invalid extension ID '{ext['id']}': "
                 "must be lowercase alphanumeric with hyphens only"
@@ -2576,6 +2598,14 @@ def download_extension(
         """
         import urllib.error
 
+        if not isinstance(extension_id, str) or not EXTENSION_ID_PATTERN.match(
+            extension_id
+        ):
+            raise ExtensionError(
+                f"Invalid extension ID '{extension_id}': "
+                "must be lowercase alphanumeric with hyphens only"
+            )
+
         # Get extension info from catalog
         ext_info = self.get_extension_info(extension_id)
         if not ext_info:
@@ -2608,9 +2638,13 @@ def download_extension(
             target_dir = self.cache_dir / "downloads"
         target_dir.mkdir(parents=True, exist_ok=True)
 
-        version = ext_info.get("version", "unknown")
+        version = _safe_version_token(ext_info.get("version"))
         zip_filename = f"{extension_id}-{version}.zip"
         zip_path = target_dir / zip_filename
+        try:
+            zip_path.resolve().relative_to(target_dir.resolve())
+        except ValueError as e:
+            raise ExtensionError(f"Refusing unsafe extension ZIP path: {zip_filename}") from e
 
         extra_headers = None
         resolved_download_url = self._resolve_github_release_asset_api_url(download_url)
diff --git a/src/specify_cli/extensions/_commands.py b/src/specify_cli/extensions/_commands.py
index 6821419b30..a1168630aa 100644
--- a/src/specify_cli/extensions/_commands.py
+++ b/src/specify_cli/extensions/_commands.py
@@ -38,6 +38,30 @@
 extension_app.add_typer(catalog_app, name="catalog")
 
 
+def _catalog_str(ext: dict, key: str, fallback: str = "") -> str:
+    """Read a catalog string field, treating JSON null / non-strings / blanks
+    as missing so they fall back instead of rendering as the literal "None".
+
+    Catalog entries are untrusted (remote/community catalogs); ``dict.get(key,
+    default)`` only substitutes the default when the key is absent, so an
+    explicit ``null`` value would otherwise reach ``str()`` and print "None".
+    """
+    value = ext.get(key)
+    if isinstance(value, str):
+        stripped = value.strip()
+        if stripped:
+            return stripped
+    return fallback
+
+
+def _catalog_id(ext: dict) -> str:
+    """Return a usable extension id, or "" when the catalog entry lacks a
+    valid one. An empty result means callers should skip the install hint (and
+    ideally the entry) rather than emit a command ``download_extension()`` will
+    refuse."""
+    return _catalog_str(ext, "id")
+
+
 # Root helpers re-fetched at call time so test monkeypatching of
 # `specify_cli.<name>` keeps working after the move.
 def _require_specify_project(*args, **kwargs):
@@ -168,7 +192,7 @@ def _resolve_catalog_extension(
 
         # Try by display name - search using argument as query, then filter for exact match
         search_results = catalog.search(query=argument)
-        name_matches = [ext for ext in search_results if ext["name"].lower() == argument.lower()]
+        name_matches = [ext for ext in search_results if str(ext.get("name", "")).lower() == argument.lower()]
 
         if len(name_matches) == 1:
             return (name_matches[0], None)
@@ -207,22 +231,30 @@ def extension_list(
     available: bool = typer.Option(False, "--available", help="Show available extensions from catalog"),
     all_extensions: bool = typer.Option(False, "--all", help="Show both installed and available"),
 ):
-    """List installed extensions."""
-    from . import ExtensionManager
+    """List installed extensions, and available catalog extensions with --available/--all."""
+    from . import ExtensionManager, ExtensionCatalog, ExtensionError
 
     project_root = _require_specify_project()
     manager = ExtensionManager(project_root)
     installed = manager.list_installed()
 
-    if not installed and not (available or all_extensions):
+    # Default (no flags) lists installed; --all also lists installed.
+    # --available alone lists only catalog extensions, not installed.
+    show_installed = all_extensions or not available
+    show_available = available or all_extensions
+
+    if not installed and not show_available:
         console.print("[yellow]No extensions installed.[/yellow]")
         console.print("\nInstall an extension with:")
         console.print("  specify extension add <extension-name>")
         return
 
-    if installed:
+    if show_installed:
         console.print("\n[bold cyan]Installed Extensions:[/bold cyan]\n")
 
+        if not installed:
+            console.print("  [dim]No extensions installed.[/dim]")
+            console.print()
         for ext in installed:
             status_icon = "✓" if ext["enabled"] else "✗"
             status_color = "green" if ext["enabled"] else "red"
@@ -233,9 +265,46 @@ def extension_list(
             console.print(f"     Commands: {ext['command_count']} | Hooks: {ext['hook_count']} | Priority: {ext['priority']} | Status: {'Enabled' if ext['enabled'] else 'Disabled'}")
             console.print()
 
-    if available or all_extensions:
-        console.print("\nInstall an extension:")
-        console.print("  [cyan]specify extension add <name>[/cyan]")
+    if show_available:
+        # Query the catalog and show extensions that are not already installed.
+        catalog = ExtensionCatalog(project_root)
+        installed_ids = {ext["id"] for ext in installed}
+
+        try:
+            results = catalog.search()
+        except ExtensionError as e:
+            console.print(f"\n[red]Error:[/red] Could not query extension catalog: {_escape_markup(str(e))}")
+            console.print("[dim]The catalog may be temporarily unavailable. Try again later.[/dim]")
+            raise typer.Exit(1)
+
+        available_exts = [ext for ext in results if ext.get("id") not in installed_ids]
+
+        console.print("\n[bold cyan]Available Extensions:[/bold cyan]\n")
+        if not available_exts:
+            console.print("  [dim]No additional extensions available in the catalog.[/dim]")
+        else:
+            for ext in available_exts:
+                # Catalog fields are untrusted (remote/community catalogs); escape
+                # before embedding in Rich markup to prevent markup injection.
+                # A missing/blank id means the entry cannot be installed, so skip
+                # it entirely rather than printing a bogus install hint.
+                extension_id = _catalog_id(ext)
+                if not extension_id:
+                    continue
+                safe_id = _escape_markup(extension_id)
+                verified_badge = " [green]✓ Verified[/green]" if ext.get("verified") else ""
+                safe_name = _escape_markup(_catalog_str(ext, "name", "(unnamed)"))
+                safe_version = _escape_markup(_catalog_str(ext, "version", "?"))
+                console.print(f"  [bold]{safe_name}[/bold] (v{safe_version}){verified_badge}")
+                console.print(f"     [dim]{safe_id}[/dim]")
+                console.print(f"     {_escape_markup(_catalog_str(ext, 'description'))}")
+                install_allowed = ext.get("_install_allowed", True)
+                if install_allowed:
+                    console.print(f"     [cyan]Install:[/cyan] specify extension add {safe_id}")
+                else:
+                    catalog_name = _escape_markup(_catalog_str(ext, "_catalog_name"))
+                    console.print(f"     [yellow]Discovery only — not installable from '{catalog_name}'[/yellow]")
+                console.print()
 
 
 @catalog_app.command("list")
@@ -601,7 +670,7 @@ def extension_add(
 
                         # Download extension ZIP (use resolved ID, not original argument which may be display name)
                         extension_id = ext_info['id']
-                        console.print(f"Downloading {_escape_markup(str(ext_info['name']))} v{_escape_markup(str(ext_info.get('version', 'unknown')))}...")
+                        console.print(f"Downloading {_escape_markup(str(ext_info.get('name', extension_id)))} v{_escape_markup(str(ext_info.get('version', 'unknown')))}...")
                         zip_path = catalog.download_extension(extension_id)
 
                         try:
@@ -751,13 +820,20 @@ def extension_search(
         console.print(f"\n[green]Found {len(results)} extension(s):[/green]\n")
 
         for ext in results:
+            # Catalog entries are untrusted; a missing/blank id cannot be
+            # installed or referenced, so skip it rather than emit a bogus
+            # install hint or crash on ext['id'].
+            extension_id = _catalog_id(ext)
+            if not extension_id:
+                continue
+
             # Extension header
             verified_badge = " [green]✓ Verified[/green]" if ext.get("verified") else ""
-            console.print(f"[bold]{_escape_markup(str(ext['name']))}[/bold] (v{_escape_markup(str(ext['version']))}){verified_badge}")
-            console.print(f"  {_escape_markup(str(ext['description']))}")
+            console.print(f"[bold]{_escape_markup(_catalog_str(ext, 'name', '(unnamed)'))}[/bold] (v{_escape_markup(_catalog_str(ext, 'version', '?'))}){verified_badge}")
+            console.print(f"  {_escape_markup(_catalog_str(ext, 'description'))}")
 
             # Metadata
-            console.print(f"\n  [dim]Author:[/dim] {_escape_markup(str(ext.get('author', 'Unknown')))}")
+            console.print(f"\n  [dim]Author:[/dim] {_escape_markup(_catalog_str(ext, 'author', 'Unknown'))}")
             if ext.get('tags'):
                 tags_str = ", ".join(str(t) for t in ext['tags'])
                 console.print(f"  [dim]Tags:[/dim] {_escape_markup(tags_str)}")
@@ -776,7 +852,7 @@ def extension_search(
             if ext.get('downloads') is not None:
                 stats.append(f"Downloads: {ext['downloads']:,}")
             if ext.get('stars') is not None:
-                stats.append(f"Stars: {ext['stars']}")
+                stats.append(f"Stars: {_escape_markup(str(ext['stars']))}")
             if stats:
                 console.print(f"  [dim]{' | '.join(stats)}[/dim]")
 
@@ -785,7 +861,7 @@ def extension_search(
                 console.print(f"  [dim]Repository:[/dim] {_escape_markup(str(ext['repository']))}")
 
             # Install command (show warning if not installable)
-            safe_id = _escape_markup(str(ext['id']))
+            safe_id = _escape_markup(extension_id)
             if install_allowed:
                 console.print(f"\n  [cyan]Install:[/cyan] specify extension add {safe_id}")
             else:
@@ -897,17 +973,17 @@ def _print_extension_info(ext_info: dict, manager):
 
     # Header
     verified_badge = " [green]✓ Verified[/green]" if ext_info.get("verified") else ""
-    console.print(f"\n[bold]{_escape_markup(str(ext_info['name']))}[/bold] (v{_escape_markup(str(ext_info['version']))}){verified_badge}")
+    console.print(f"\n[bold]{_escape_markup(_catalog_str(ext_info, 'name', '(unnamed)'))}[/bold] (v{_escape_markup(_catalog_str(ext_info, 'version', '?'))}){verified_badge}")
     console.print(f"ID: {_escape_markup(str(ext_info['id']))}")
     console.print()
 
     # Description
-    console.print(f"{_escape_markup(str(ext_info['description']))}")
+    console.print(f"{_escape_markup(_catalog_str(ext_info, 'description'))}")
     console.print()
 
     # Author and License
-    console.print(f"[dim]Author:[/dim] {_escape_markup(str(ext_info.get('author', 'Unknown')))}")
-    console.print(f"[dim]License:[/dim] {_escape_markup(str(ext_info.get('license', 'Unknown')))}")
+    console.print(f"[dim]Author:[/dim] {_escape_markup(_catalog_str(ext_info, 'author', 'Unknown'))}")
+    console.print(f"[dim]License:[/dim] {_escape_markup(_catalog_str(ext_info, 'license', 'Unknown'))}")
 
     # Category and Effect
     if ext_info.get('category'):
@@ -923,23 +999,26 @@ def _print_extension_info(ext_info: dict, manager):
     console.print()
 
     # Requirements
-    if ext_info.get('requires'):
+    reqs = ext_info.get('requires')
+    if isinstance(reqs, dict) and reqs:
         console.print("[bold]Requirements:[/bold]")
-        reqs = ext_info['requires']
         if reqs.get('speckit_version'):
             console.print(f"  • Spec Kit: {_escape_markup(str(reqs['speckit_version']))}")
-        if reqs.get('tools'):
-            for tool in reqs['tools']:
-                tool_name = _escape_markup(str(tool['name']))
+        tools = reqs.get('tools')
+        if isinstance(tools, list):
+            for tool in tools:
+                if not isinstance(tool, dict):
+                    continue
+                tool_name = _escape_markup(str(tool.get('name', '(unnamed)')))
                 tool_version = _escape_markup(str(tool.get('version', 'any')))
                 required = " (required)" if tool.get('required') else " (optional)"
                 console.print(f"  • {tool_name}: {tool_version}{required}")
         console.print()
 
     # Provides
-    if ext_info.get('provides'):
+    provides = ext_info.get('provides')
+    if isinstance(provides, dict) and provides:
         console.print("[bold]Provides:[/bold]")
-        provides = ext_info['provides']
         if provides.get('commands'):
             console.print(f"  • Commands: {_escape_markup(str(provides['commands']))}")
         if provides.get('hooks'):
@@ -957,7 +1036,7 @@ def _print_extension_info(ext_info: dict, manager):
     if ext_info.get('downloads') is not None:
         stats.append(f"Downloads: {ext_info['downloads']:,}")
     if ext_info.get('stars') is not None:
-        stats.append(f"Stars: {ext_info['stars']}")
+        stats.append(f"Stars: {_escape_markup(str(ext_info['stars']))}")
     if stats:
         console.print(f"[bold]Statistics:[/bold] {' | '.join(stats)}")
         console.print()
@@ -1064,8 +1143,8 @@ def extension_update(
                 continue
 
             try:
-                catalog_version = pkg_version.Version(ext_info["version"])
-            except pkg_version.InvalidVersion:
+                catalog_version = pkg_version.Version(str(ext_info["version"]))
+            except (pkg_version.InvalidVersion, KeyError):
                 console.print(
                     f"⚠  {safe_ext_id}: Invalid catalog version '{_escape_markup(str(ext_info.get('version')))}' (skipping)"
                 )
diff --git a/tests/test_extension_add_path_traversal.py b/tests/test_extension_add_path_traversal.py
new file mode 100644
index 0000000000..e8aad49a49
--- /dev/null
+++ b/tests/test_extension_add_path_traversal.py
@@ -0,0 +1,82 @@
+"""Security test for `specify extension add <label> --from <url>`.
+
+A label containing path separators (e.g. "../../etc/evil") must not let the
+download escape the downloads cache directory. The handler does not let the
+label participate in the path at all: it downloads to a generated tempfile
+(``extension-url-download-*.zip``) created with ``dir=download_dir``, so the
+filename is machine-generated and confined to the downloads cache. This test
+asserts the resulting path stays inside that directory and carries no path
+separators from the raw label.
+"""
+
+import contextlib
+
+import pytest
+from typer.testing import CliRunner
+
+from specify_cli import app
+from specify_cli.extensions import ExtensionManager
+
+runner = CliRunner()
+
+
+@pytest.fixture
+def project_dir(tmp_path):
+    proj_dir = tmp_path / "project"
+    proj_dir.mkdir()
+    (proj_dir / ".specify").mkdir()
+    (proj_dir / ".specify" / "config.toml").write_text("ai = 'claude'")
+    return proj_dir
+
+
+def test_add_from_url_sanitizes_traversal_label(project_dir, monkeypatch):
+    monkeypatch.chdir(project_dir)
+
+    captured = {}
+
+    # A minimal but valid ZIP archive: the `add --from` flow validates the
+    # downloaded bytes are a real ZIP before installing, so a non-ZIP body would
+    # be rejected upstream of the path-sanitization under test.
+    import io
+    import zipfile
+
+    _zip_buf = io.BytesIO()
+    with zipfile.ZipFile(_zip_buf, "w") as _zf:
+        _zf.writestr("extension.yaml", "name: evil\n")
+    valid_zip_bytes = _zip_buf.getvalue()
+
+    @contextlib.contextmanager
+    def fake_open_url(url, timeout=60, extra_headers=None):
+        class _Resp:
+            def read(self):
+                return valid_zip_bytes
+        yield _Resp()
+
+    monkeypatch.setattr("specify_cli.authentication.http.open_url", fake_open_url)
+
+    def fake_install_from_zip(self, zip_path, *args, **kwargs):
+        captured["zip_path"] = zip_path
+        # Stop the flow before real install/registration runs.
+        raise RuntimeError("stop after capture")
+
+    monkeypatch.setattr(ExtensionManager, "install_from_zip", fake_install_from_zip)
+
+    malicious = "../../../etc/evil"
+    runner.invoke(
+        app,
+        ["extension", "add", malicious, "--from", "https://example.com/payload.zip"],
+        obj={"project_root": project_dir},
+        input="y\n",  # confirm the "Untrusted Source" prompt for --from URLs
+    )
+
+    zip_path = captured.get("zip_path")
+    assert zip_path is not None, "install_from_zip was never reached"
+
+    download_dir = (project_dir / ".specify" / "extensions" / ".cache" / "downloads").resolve()
+    resolved = zip_path.resolve()
+
+    # The download must stay inside the downloads cache dir...
+    assert resolved.parent == download_dir
+    # ...and the filename must not carry path separators from the raw label.
+    assert "/" not in zip_path.name
+    assert ".." not in zip_path.name
diff --git a/tests/test_extension_catalog_robustness.py b/tests/test_extension_catalog_robustness.py
new file mode 100644
index 0000000000..3b27ee3798
--- /dev/null
+++ b/tests/test_extension_catalog_robustness.py
@@ -0,0 +1,295 @@
+"""Robustness tests for catalog-driven extension commands.
+
+Catalog entries are untrusted (remote/community catalogs) and only guaranteed
+to be dicts with an injected ``id`` — ``_get_merged_extensions`` does not
+validate any other field. ``extension search`` and ``extension info`` must
+therefore tolerate entries missing ``name``/``version``/``description`` (no
+KeyError), entries whose ``requires``/``provides`` are non-dicts (no
+AttributeError), and must escape catalog-controlled values like ``stars``
+before printing them as Rich markup.
+"""
+
+import pytest
+from typer.testing import CliRunner
+
+from specify_cli import app
+from specify_cli.extensions import ExtensionError, ExtensionManager, ExtensionCatalog
+
+runner = CliRunner()
+
+
+@pytest.fixture
+def project_dir(tmp_path):
+    proj_dir = tmp_path / "project"
+    proj_dir.mkdir()
+    (proj_dir / ".specify").mkdir()
+    (proj_dir / ".specify" / "config.toml").write_text("ai = 'claude'")
+    return proj_dir
+
+
+def test_search_tolerates_entry_missing_name_version_description(project_dir, monkeypatch):
+    """A malformed catalog entry must not crash `extension search`."""
+    monkeypatch.chdir(project_dir)
+
+    monkeypatch.setattr(
+        ExtensionCatalog,
+        "search",
+        lambda self, **kwargs: [{"id": "broken-ext"}],  # only id present
+    )
+
+    result = runner.invoke(app, ["extension", "search"], obj={"project_root": project_dir})
+
+    assert result.exit_code == 0, result.output
+    assert "broken-ext" in result.output
+    assert "(unnamed)" in result.output
+    assert "(v?)" in result.output
+
+
+def test_search_json_null_fields_render_placeholders_not_none(project_dir, monkeypatch):
+    """Explicit JSON null fields must fall back, not render the literal "None".
+
+    ``dict.get(key, default)`` only substitutes on an absent key; an explicit
+    ``null`` value reaches ``str()`` and would print "None". Name/version/
+    description/author must degrade to placeholders instead.
+    """
+    monkeypatch.chdir(project_dir)
+
+    monkeypatch.setattr(
+        ExtensionCatalog,
+        "search",
+        lambda self, **kwargs: [{
+            "id": "null-ext",
+            "name": None,
+            "version": None,
+            "description": None,
+            "author": None,
+        }],
+    )
+
+    result = runner.invoke(app, ["extension", "search"], obj={"project_root": project_dir})
+
+    assert result.exit_code == 0, result.output
+    assert "null-ext" in result.output
+    assert "(unnamed)" in result.output
+    assert "(v?)" in result.output
+    assert "Unknown" in result.output  # author fallback
+    # The literal string "None" must never leak into rendered output.
+    assert "None" not in result.output
+
+
+@pytest.mark.parametrize("bad_id", [None, "", "   "])
+def test_search_skips_entries_without_valid_id(project_dir, monkeypatch, bad_id):
+    """Entries with a missing/blank/null id are skipped entirely.
+
+    Such an id cannot be installed (``download_extension()`` refuses it) and
+    previously crashed on ``ext['id']`` when absent. Skip the whole entry
+    rather than emit a bogus/dangling install hint.
+    """
+    monkeypatch.chdir(project_dir)
+
+    monkeypatch.setattr(
+        ExtensionCatalog,
+        "search",
+        lambda self, **kwargs: [
+            {"id": bad_id, "name": "Ghost Ext", "version": "1.0.0", "description": "d"},
+            {"id": "real-ext", "name": "Real Ext", "version": "1.0.0", "description": "d"},
+        ],
+    )
+
+    result = runner.invoke(app, ["extension", "search"], obj={"project_root": project_dir})
+
+    assert result.exit_code == 0, result.output
+    assert "real-ext" in result.output
+    assert "specify extension add real-ext" in result.output
+    # The id-less entry is dropped: no header, no dangling install hint.
+    assert "Ghost Ext" not in result.output
+
+
+def test_search_escapes_markup_in_stars(project_dir, monkeypatch):
+    """Catalog-controlled `stars` must be escaped, not parsed as Rich markup."""
+    monkeypatch.chdir(project_dir)
+
+    monkeypatch.setattr(
+        ExtensionCatalog,
+        "search",
+        lambda self, **kwargs: [{
+            "id": "starry",
+            "name": "Starry",
+            "version": "1.0.0",
+            "description": "d",
+            "stars": "[red]999[/red]",
+        }],
+    )
+
+    result = runner.invoke(app, ["extension", "search"], obj={"project_root": project_dir})
+
+    assert result.exit_code == 0, result.output
+    # Escaped markup is rendered literally rather than swallowed by Rich.
+    assert "[red]999[/red]" in result.output
+
+
+def test_info_tolerates_missing_fields_and_non_dict_sections(project_dir, monkeypatch):
+    """`extension info` must survive a malformed catalog entry.
+
+    Missing name/version/description → placeholders (no KeyError); requires as a
+    list and provides as a string → skipped, not `.get()`-crashed.
+    """
+    monkeypatch.chdir(project_dir)
+
+    monkeypatch.setattr(ExtensionManager, "list_installed", lambda self: [])
+    monkeypatch.setattr(
+        ExtensionCatalog,
+        "get_extension_info",
+        lambda self, ext_id: {
+            "id": "broken-ext",
+            "requires": ["not", "a", "dict"],
+            "provides": "junk",
+            "stars": "[bold]42[/bold]",
+        },
+    )
+
+    result = runner.invoke(app, ["extension", "info", "broken-ext"], obj={"project_root": project_dir})
+
+    assert result.exit_code == 0, result.output
+    assert "broken-ext" in result.output
+    assert "(unnamed)" in result.output
+    assert "(v?)" in result.output
+    # Non-dict requires/provides are skipped, not crashed on.
+    assert "Requirements:" not in result.output
+    assert "Provides:" not in result.output
+    # stars is escaped.
+    assert "[bold]42[/bold]" in result.output
+
+
+def test_download_rejects_catalog_id_path_traversal(project_dir, monkeypatch):
+    """Catalog-controlled IDs must not become path-traversing ZIP filenames."""
+    monkeypatch.chdir(project_dir)
+
+    catalog = ExtensionCatalog(project_dir)
+    malicious_id = "../escape"
+
+    monkeypatch.setattr(
+        catalog,
+        "_get_merged_extensions",
+        lambda: [{
+            "id": malicious_id,
+            "name": "Evil",
+            "version": "1.0.0",
+            "download_url": "https://example.com/evil.zip",
+        }],
+    )
+
+    def fail_open_url(*args, **kwargs):
+        raise AssertionError("download should not be attempted for an unsafe id")
+
+    monkeypatch.setattr(catalog, "_open_url", fail_open_url)
+
+    with pytest.raises(ExtensionError, match="Invalid extension ID"):
+        catalog.download_extension(malicious_id)
+
+
+def test_info_json_null_fields_render_placeholders_not_none(project_dir, monkeypatch):
+    """`extension info` must coalesce JSON null fields, not print "None".
+
+    ``get_extension_info`` returns the raw merged catalog entry unmodified, so
+    an explicit ``null`` name/version/description/author/license reaches the
+    renderer. These must degrade to their placeholders, mirroring the fix
+    already applied to `list --available` and `search`.
+    """
+    monkeypatch.chdir(project_dir)
+
+    monkeypatch.setattr(ExtensionManager, "list_installed", lambda self: [])
+    monkeypatch.setattr(
+        ExtensionCatalog,
+        "get_extension_info",
+        lambda self, ext_id: {
+            "id": "null-ext",
+            "name": None,
+            "version": None,
+            "description": None,
+            "author": None,
+            "license": None,
+        },
+    )
+
+    result = runner.invoke(app, ["extension", "info", "null-ext"], obj={"project_root": project_dir})
+
+    assert result.exit_code == 0, result.output
+    assert "null-ext" in result.output
+    assert "(unnamed)" in result.output
+    assert "(v?)" in result.output
+    # The literal string "None" must never leak into rendered output.
+    assert "None" not in result.output
+
+
+@pytest.mark.parametrize(
+    "raw, expected",
+    [
+        ("1.2.3", "1.2.3"),          # normal version untouched
+        ("1.0/../x", "1.0-..-x"),    # separators collapse to a single segment
+        ("../../etc", "etc"),        # leading traversal stripped
+        ("a b\\c/d", "a-b-c-d"),     # spaces and both slash kinds collapse
+        ("..", "unknown"),           # pure traversal degrades to fallback
+        ("   ", "unknown"),          # blank degrades to fallback
+        (None, "unknown"),           # JSON null degrades to fallback
+        (123, "unknown"),            # non-string degrades to fallback
+    ],
+)
+def test_safe_version_token_strips_separators(raw, expected):
+    """Version tokens used in ZIP filenames must never carry path separators."""
+    from specify_cli.extensions import _safe_version_token
+
+    token = _safe_version_token(raw)
+    assert token == expected
+    assert "/" not in token and "\\" not in token
+
+
+def test_download_sanitizes_catalog_version_into_safe_filename(project_dir, monkeypatch):
+    """A catalog version with separators must not yield a nested/escaping path.
+
+    The pre-fix code used the version verbatim, so ``1.0/evil`` produced a
+    nested path that stayed inside the target dir (passing the ``resolve()``
+    guard) yet failed to write. Sanitizing the version keeps the ZIP a single
+    filename directly under the target directory.
+    """
+    monkeypatch.chdir(project_dir)
+
+    catalog = ExtensionCatalog(project_dir)
+    target_dir = project_dir / "downloads"
+    target_dir.mkdir()
+
+    monkeypatch.setattr(
+        catalog,
+        "_get_merged_extensions",
+        lambda: [{
+            "id": "good-ext",
+            "name": "Good",
+            "version": "1.0/evil",
+            "download_url": "https://example.com/good.zip",
+        }],
+    )
+
+    class _FakeResponse:
+        def __enter__(self):
+            return self
+
+        def __exit__(self, *exc):
+            return False
+
+        def read(self):
+            return b"zip-bytes"
+
+    monkeypatch.setattr(catalog, "_open_url", lambda *a, **k: _FakeResponse())
+    monkeypatch.setattr(catalog, "_resolve_github_release_asset_api_url", lambda url: None)
+    # Skip integrity check (no sha256 in this fixture entry).
+    import specify_cli.extensions as ext_module
+    monkeypatch.setattr(ext_module, "verify_archive_sha256", lambda *a, **k: None)
+
+    zip_path = catalog.download_extension("good-ext", target_dir=target_dir)
+
+    # The ZIP is a single file directly under target_dir — no nested dirs,
+    # no separators leaked from the version.
+    assert zip_path.parent == target_dir
+    assert "/" not in zip_path.name and "\\" not in zip_path.name
+    assert zip_path.name == "good-ext-1.0-evil.zip"
+    assert zip_path.read_bytes() == b"zip-bytes"
diff --git a/tests/test_extension_list_available.py b/tests/test_extension_list_available.py
new file mode 100644
index 0000000000..8b0d1e6668
--- /dev/null
+++ b/tests/test_extension_list_available.py
@@ -0,0 +1,208 @@
+"""Behavior tests for `specify extension list --available/--all`.
+
+These flags were documented from the original extension system (#1551) as
+"Show available extensions from catalog", but the implementation was a static
+hint that never queried the catalog. This suite covers the wired-up behavior:
+the catalog is queried, already-installed IDs are filtered out, and a clear
+error is surfaced when the catalog is unavailable.
+"""
+
+import pytest
+from typer.testing import CliRunner
+
+from specify_cli import app
+from specify_cli.extensions import ExtensionManager, ExtensionCatalog, ExtensionError
+
+runner = CliRunner()
+
+
+@pytest.fixture
+def project_dir(tmp_path):
+    """Create a minimal spec-kit project directory."""
+    proj_dir = tmp_path / "project"
+    proj_dir.mkdir()
+    (proj_dir / ".specify").mkdir()
+    (proj_dir / ".specify" / "config.toml").write_text("ai = 'claude'")
+    return proj_dir
+
+
+def _catalog_entry(ext_id, name, version="1.0.0", verified=False, install_allowed=True, catalog_name="default"):
+    return {
+        "id": ext_id,
+        "name": name,
+        "version": version,
+        "description": f"{name} description",
+        "verified": verified,
+        "_install_allowed": install_allowed,
+        "_catalog_name": catalog_name,
+    }
+
+
+def test_list_available_queries_catalog_and_filters_installed(project_dir, monkeypatch):
+    """--available must query the catalog and drop already-installed IDs."""
+    monkeypatch.chdir(project_dir)
+
+    monkeypatch.setattr(ExtensionManager, "list_installed", lambda self: [{"id": "already-installed"}])
+    monkeypatch.setattr(ExtensionCatalog, "search", lambda self: [
+        _catalog_entry("already-installed", "Already Installed"),
+        _catalog_entry("fresh-ext", "Fresh Ext", verified=True),
+    ])
+
+    result = runner.invoke(app, ["extension", "list", "--available"], obj={"project_root": project_dir})
+
+    assert result.exit_code == 0
+    assert "Available Extensions:" in result.output
+    # Uninstalled catalog extension is shown...
+    assert "fresh-ext" in result.output
+    assert "✓ Verified" in result.output
+    assert "specify extension add fresh-ext" in result.output
+    # ...and the installed one is filtered out.
+    assert "already-installed" not in result.output
+
+
+def test_list_available_marks_discovery_only_entries(project_dir, monkeypatch):
+    """Entries whose catalog disallows install render a discovery-only note."""
+    monkeypatch.chdir(project_dir)
+
+    monkeypatch.setattr(ExtensionManager, "list_installed", lambda self: [])
+    monkeypatch.setattr(ExtensionCatalog, "search", lambda self: [
+        _catalog_entry("locked-ext", "Locked Ext", install_allowed=False, catalog_name="curated"),
+    ])
+
+    result = runner.invoke(app, ["extension", "list", "--available"], obj={"project_root": project_dir})
+
+    assert result.exit_code == 0
+    assert "Discovery only" in result.output
+    assert "curated" in result.output
+    assert "specify extension add locked-ext" not in result.output
+
+
+def test_list_available_empty_catalog_message(project_dir, monkeypatch):
+    """An empty (post-filter) catalog reports no additional extensions."""
+    monkeypatch.chdir(project_dir)
+
+    monkeypatch.setattr(ExtensionManager, "list_installed", lambda self: [])
+    monkeypatch.setattr(ExtensionCatalog, "search", lambda self: [])
+
+    result = runner.invoke(app, ["extension", "list", "--available"], obj={"project_root": project_dir})
+
+    assert result.exit_code == 0
+    assert "Available Extensions:" in result.output
+    assert "No additional extensions available" in result.output
+
+
+def test_list_available_catalog_error_exits(project_dir, monkeypatch):
+    """A catalog failure surfaces a clear error and exits non-zero."""
+    monkeypatch.chdir(project_dir)
+
+    def _boom(self):
+        raise ExtensionError("catalog unreachable")
+
+    monkeypatch.setattr(ExtensionManager, "list_installed", lambda self: [])
+    monkeypatch.setattr(ExtensionCatalog, "search", _boom)
+
+    result = runner.invoke(app, ["extension", "list", "--available"], obj={"project_root": project_dir})
+
+    assert result.exit_code == 1
+    assert "Could not query extension catalog" in result.output
+    assert "catalog unreachable" in result.output
+
+
+def test_list_available_tolerates_entry_missing_name_or_version(project_dir, monkeypatch):
+    """A malformed catalog entry missing name/version must not crash listing.
+
+    Catalog entries are untrusted (remote/community catalogs) and only
+    guaranteed to be dicts with an injected ``id``. A missing ``name`` or
+    ``version`` must degrade to a placeholder, not raise KeyError.
+    """
+    monkeypatch.chdir(project_dir)
+
+    monkeypatch.setattr(ExtensionManager, "list_installed", lambda self: [])
+    monkeypatch.setattr(ExtensionCatalog, "search", lambda self: [
+        {"id": "broken-ext"},  # no name, no version, no description
+    ])
+
+    result = runner.invoke(app, ["extension", "list", "--available"], obj={"project_root": project_dir})
+
+    assert result.exit_code == 0
+    assert "broken-ext" in result.output
+    assert "(unnamed)" in result.output
+    assert "(v?)" in result.output
+
+
+def test_list_available_json_null_fields_render_placeholders_not_none(project_dir, monkeypatch):
+    """Explicit JSON null fields must fall back, not render the literal "None".
+
+    ``dict.get(key, default)`` only substitutes when the key is absent; an
+    explicit ``null`` value reaches ``str()`` and would print "None". Untrusted
+    catalog JSON can carry nulls, so name/version/description must degrade to
+    their placeholders instead.
+    """
+    monkeypatch.chdir(project_dir)
+
+    monkeypatch.setattr(ExtensionManager, "list_installed", lambda self: [])
+    monkeypatch.setattr(ExtensionCatalog, "search", lambda self: [
+        {"id": "null-ext", "name": None, "version": None, "description": None},
+    ])
+
+    result = runner.invoke(app, ["extension", "list", "--available"], obj={"project_root": project_dir})
+
+    assert result.exit_code == 0
+    assert "null-ext" in result.output
+    assert "(unnamed)" in result.output
+    assert "(v?)" in result.output
+    # The literal string "None" must never leak into the rendered output.
+    assert "None" not in result.output
+
+
+@pytest.mark.parametrize("bad_id", [None, "", "   "])
+def test_list_available_skips_entries_without_valid_id(project_dir, monkeypatch, bad_id):
+    """Entries with a missing/blank/null id are skipped entirely.
+
+    Such an id cannot be installed (``download_extension()`` would refuse it),
+    so printing an install hint like ``specify extension add`` with no id — or
+    with ``None`` — only misleads the user. Skip the whole entry.
+    """
+    monkeypatch.chdir(project_dir)
+
+    monkeypatch.setattr(ExtensionManager, "list_installed", lambda self: [])
+    monkeypatch.setattr(ExtensionCatalog, "search", lambda self: [
+        {"id": bad_id, "name": "Ghost Ext", "version": "1.0.0"},
+        _catalog_entry("real-ext", "Real Ext"),
+    ])
+
+    result = runner.invoke(app, ["extension", "list", "--available"], obj={"project_root": project_dir})
+
+    assert result.exit_code == 0
+    # The valid entry still renders with its install hint...
+    assert "real-ext" in result.output
+    assert "specify extension add real-ext" in result.output
+    # ...but the id-less entry is dropped: no name, no dangling install hint.
+    assert "Ghost Ext" not in result.output
+
+
+def test_list_all_shows_installed_and_available(project_dir, monkeypatch):
+    """--all lists installed extensions and available catalog extensions."""
+    monkeypatch.chdir(project_dir)
+
+    monkeypatch.setattr(ExtensionManager, "list_installed", lambda self: [{
+        "id": "my-ext",
+        "name": "My Ext",
+        "version": "2.0.0",
+        "description": "installed one",
+        "command_count": 1,
+        "hook_count": 0,
+        "priority": 10,
+        "enabled": True,
+    }])
+    monkeypatch.setattr(ExtensionCatalog, "search", lambda self: [
+        _catalog_entry("other-ext", "Other Ext"),
+    ])
+
+    result = runner.invoke(app, ["extension", "list", "--all"], obj={"project_root": project_dir})
+
+    assert result.exit_code == 0
+    assert "Installed Extensions:" in result.output
+    assert "My Ext" in result.output
+    assert "Available Extensions:" in result.output
+    assert "other-ext" in result.output