The twisted.web.util.redirectTo function contains an HTML injection vulnerability. If application code allows an attacker to control the redirect URL this vulnerability may result in Reflected Cross-Site Scripting (XSS) in the redirect response HTML body.
Twisted’s redirectTo function generates an HTTP 302 Redirect response. The response contains an HTML body, built for exceptional cases where the browser doesn’t properly handle the redirect, allowing the user to click a link, navigating them to the specified destination.
The function reflects the destination URL in the HTML body without any output encoding.
# https://github.com/twisted/twisted/blob/trunk/src/twisted/web/_template_util.py#L88
def redirectTo(URL: bytes, request: IRequest) -> bytes:
# ---snip---
content = b"""
<html>
<head>
<meta http-equiv=\"refresh\" content=\"0;URL=%(url)s\">
</head>
<body bgcolor=\"#FFFFFF\" text=\"#000000\">
<a href=\"%(url)s\">click here</a>
</body>
</html>
""" % {
b"url": URL
}
return content
If an attacker has full or partial control over redirect location due to an application bug, also known as an “Open Redirect”, they may inject arbitrary HTML into the response’s body, ultimately leading to an XSS attack.
It’s worth noting that the issue is known to maintainers and tracked with GitHub Issue#9839. The issue description, however, does not make any mention of exploitability and simply states: “…Browsers don't seem to actually render that page…”
The issue can be reproduced by running the following Twisted-based HTTP server locally:
from twisted.web import server, resource
from twisted.internet import reactor
from twisted.web.util import redirectTo
class Simple(resource.Resource):
isLeaf = True
def render_GET(self, request):
url = request.args[b'url'][0] # <-- open redirect
return...
24.7.0rc1Exploitability
AV:NAC:LAT:NPR:NUI:PVulnerable System
VC:NVI:NVA:NSubsequent System
SC:LSI:LSA:N5.3/CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N