Moderate severityNVD Advisory· Published Apr 18, 2024· Updated Nov 3, 2025

aiohttp vulnerable to XSS on index pages for static file handling

CVE-2024-27306

Description

aiohttp is an asynchronous HTTP client/server framework for asyncio and Python. A XSS vulnerability exists on index pages for static file handling. This vulnerability is fixed in 3.9.4. We have always recommended using a reverse proxy server (e.g. nginx) for serving static files. Users following the recommendation are unaffected. Other users can disable show_index if unable to upgrade.

Affected packages

Versions sourced from the GitHub Security Advisory.

Package	Affected versions	Patched versions
aiohttpPyPI	< 3.9.4	3.9.4

Affected products

Aio Libs/Aiohttpv5
Range: < 3.9.4

Patches

28335525d1ea

Escape filenames and paths in HTML when generating index pages (#8317) (#8319)

https://github.com/aio-libs/aiohttpSam BullApr 11, 2024via ghsa

commit

3 files changed · +118 −19

aiohttp/web_urldispatcher.py+7 −5 modified

@@ -1,7 +1,9 @@
 import abc
 import asyncio
 import base64
+import functools
 import hashlib
+import html
 import inspect
 import keyword
 import os
@@ -90,6 +92,8 @@
 _ExpectHandler = Callable[[Request], Awaitable[Optional[StreamResponse]]]
 _Resolve = Tuple[Optional["UrlMappingMatchInfo"], Set[str]]
 
+html_escape = functools.partial(html.escape, quote=True)
+
 
 class _InfoDict(TypedDict, total=False):
     path: str
@@ -708,15 +712,15 @@ def _directory_as_html(self, filepath: Path) -> str:
         assert filepath.is_dir()
 
         relative_path_to_dir = filepath.relative_to(self._directory).as_posix()
-        index_of = f"Index of /{relative_path_to_dir}"
+        index_of = f"Index of /{html_escape(relative_path_to_dir)}"
         h1 = f"<h1>{index_of}</h1>"
 
         index_list = []
         dir_index = filepath.iterdir()
         for _file in sorted(dir_index):
             # show file url as relative to static path
             rel_path = _file.relative_to(self._directory).as_posix()
-            file_url = self._prefix + "/" + rel_path
+            quoted_file_url = _quote_path(f"{self._prefix}/{rel_path}")
 
             # if file is a directory, add '/' to the end of the name
             if _file.is_dir():
@@ -725,9 +729,7 @@ def _directory_as_html(self, filepath: Path) -> str:
                 file_name = _file.name
 
             index_list.append(
-                '<li><a href="{url}">{name}</a></li>'.format(
-                    url=file_url, name=file_name
-                )
+                f'<li><a href="{quoted_file_url}">{html_escape(file_name)}</a></li>'
             )
         ul = "<ul>\n{}\n</ul>".format("\n".join(index_list))
         body = f"<body>\n{h1}\n{ul}\n</body>"

CHANGES/8317.bugfix.rst+1 −0 added

@@ -0,0 +1 @@
+Escaped filenames in static view -- by :user:`bdraco`.

tests/test_web_urldispatcher.py+110 −14 modified

@@ -1,6 +1,7 @@
 import asyncio
 import functools
 import pathlib
+import sys
 from typing import Optional
 from unittest import mock
 from unittest.mock import MagicMock
@@ -14,31 +15,38 @@
 
 
 @pytest.mark.parametrize(
-    "show_index,status,prefix,data",
+    "show_index,status,prefix,request_path,data",
     [
-        pytest.param(False, 403, "/", None, id="index_forbidden"),
+        pytest.param(False, 403, "/", "/", None, id="index_forbidden"),
         pytest.param(
             True,
             200,
             "/",
-            b"<html>\n<head>\n<title>Index of /.</title>\n"
-            b"</head>\n<body>\n<h1>Index of /.</h1>\n<ul>\n"
-            b'<li><a href="/my_dir">my_dir/</a></li>\n'
-            b'<li><a href="/my_file">my_file</a></li>\n'
-            b"</ul>\n</body>\n</html>",
-            id="index_root",
+            "/",
+            b"<html>\n<head>\n<title>Index of /.</title>\n</head>\n<body>\n<h1>Index of"
+            b' /.</h1>\n<ul>\n<li><a href="/my_dir">my_dir/</a></li>\n<li><a href="/my_file">'
+            b"my_file</a></li>\n</ul>\n</body>\n</html>",
         ),
         pytest.param(
             True,
             200,
             "/static",
-            b"<html>\n<head>\n<title>Index of /.</title>\n"
-            b"</head>\n<body>\n<h1>Index of /.</h1>\n<ul>\n"
-            b'<li><a href="/static/my_dir">my_dir/</a></li>\n'
-            b'<li><a href="/static/my_file">my_file</a></li>\n'
-            b"</ul>\n</body>\n</html>",
+            "/static",
+            b"<html>\n<head>\n<title>Index of /.</title>\n</head>\n<body>\n<h1>Index of"
+            b' /.</h1>\n<ul>\n<li><a href="/static/my_dir">my_dir/</a></li>\n<li><a href="'
+            b'/static/my_file">my_file</a></li>\n</ul>\n</body>\n</html>',
             id="index_static",
         ),
+        pytest.param(
+            True,
+            200,
+            "/static",
+            "/static/my_dir",
+            b"<html>\n<head>\n<title>Index of /my_dir</title>\n</head>\n<body>\n<h1>"
+            b'Index of /my_dir</h1>\n<ul>\n<li><a href="/static/my_dir/my_file_in_dir">'
+            b"my_file_in_dir</a></li>\n</ul>\n</body>\n</html>",
+            id="index_subdir",
+        ),
     ],
 )
 async def test_access_root_of_static_handler(
@@ -47,6 +55,7 @@ async def test_access_root_of_static_handler(
     show_index: bool,
     status: int,
     prefix: str,
+    request_path: str,
     data: Optional[bytes],
 ) -> None:
     # Tests the operation of static file server.
@@ -72,7 +81,94 @@ async def test_access_root_of_static_handler(
     client = await aiohttp_client(app)
 
     # Request the root of the static directory.
-    async with await client.get(prefix) as r:
+    async with await client.get(request_path) as r:
+        assert r.status == status
+
+        if data:
+            assert r.headers["Content-Type"] == "text/html; charset=utf-8"
+            read_ = await r.read()
+            assert read_ == data
+
+
+@pytest.mark.internal  # Dependent on filesystem
+@pytest.mark.skipif(
+    not sys.platform.startswith("linux"),
+    reason="Invalid filenames on some filesystems (like Windows)",
+)
+@pytest.mark.parametrize(
+    "show_index,status,prefix,request_path,data",
+    [
+        pytest.param(False, 403, "/", "/", None, id="index_forbidden"),
+        pytest.param(
+            True,
+            200,
+            "/",
+            "/",
+            b"<html>\n<head>\n<title>Index of /.</title>\n</head>\n<body>\n<h1>Index of"
+            b' /.</h1>\n<ul>\n<li><a href="/%3Cimg%20src=0%20onerror=alert(1)%3E.dir">&l'
+            b't;img src=0 onerror=alert(1)&gt;.dir/</a></li>\n<li><a href="/%3Cimg%20sr'
+            b'c=0%20onerror=alert(1)%3E.txt">&lt;img src=0 onerror=alert(1)&gt;.txt</a></l'
+            b"i>\n</ul>\n</body>\n</html>",
+        ),
+        pytest.param(
+            True,
+            200,
+            "/static",
+            "/static",
+            b"<html>\n<head>\n<title>Index of /.</title>\n</head>\n<body>\n<h1>Index of"
+            b' /.</h1>\n<ul>\n<li><a href="/static/%3Cimg%20src=0%20onerror=alert(1)%3E.'
+            b'dir">&lt;img src=0 onerror=alert(1)&gt;.dir/</a></li>\n<li><a href="/stat'
+            b'ic/%3Cimg%20src=0%20onerror=alert(1)%3E.txt">&lt;img src=0 onerror=alert(1)&'
+            b"gt;.txt</a></li>\n</ul>\n</body>\n</html>",
+            id="index_static",
+        ),
+        pytest.param(
+            True,
+            200,
+            "/static",
+            "/static/<img src=0 onerror=alert(1)>.dir",
+            b"<html>\n<head>\n<title>Index of /&lt;img src=0 onerror=alert(1)&gt;.dir</t"
+            b"itle>\n</head>\n<body>\n<h1>Index of /&lt;img src=0 onerror=alert(1)&gt;.di"
+            b'r</h1>\n<ul>\n<li><a href="/static/%3Cimg%20src=0%20onerror=alert(1)%3E.di'
+            b'r/my_file_in_dir">my_file_in_dir</a></li>\n</ul>\n</body>\n</html>',
+            id="index_subdir",
+        ),
+    ],
+)
+async def test_access_root_of_static_handler_xss(
+    tmp_path: pathlib.Path,
+    aiohttp_client: AiohttpClient,
+    show_index: bool,
+    status: int,
+    prefix: str,
+    request_path: str,
+    data: Optional[bytes],
+) -> None:
+    # Tests the operation of static file server.
+    # Try to access the root of static file server, and make
+    # sure that correct HTTP statuses are returned depending if we directory
+    # index should be shown or not.
+    # Ensure that html in file names is escaped.
+    # Ensure that links are url quoted.
+    my_file = tmp_path / "<img src=0 onerror=alert(1)>.txt"
+    my_dir = tmp_path / "<img src=0 onerror=alert(1)>.dir"
+    my_dir.mkdir()
+    my_file_in_dir = my_dir / "my_file_in_dir"
+
+    with my_file.open("w") as fw:
+        fw.write("hello")
+
+    with my_file_in_dir.open("w") as fw:
+        fw.write("world")
+
+    app = web.Application()
+
+    # Register global static route:
+    app.router.add_static(prefix, str(tmp_path), show_index=show_index)
+    client = await aiohttp_client(app)
+
+    # Request the root of the static directory.
+    async with await client.get(request_path) as r:
         assert r.status == status
 
         if data:

Vulnerability mechanics

Generated by null/stub on May 9, 2026. Inputs: CWE entries + fix-commit diffs from this CVE's patches. Citations validated against bundle.

References

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cvss	0.260
epss	0.001
exploit	0.000
kev	0.000
patch	-0.070
ransomware	0.000