Headline
GHSA-cf56-g6w6-pqq2: Twisted vulnerable to HTML injection in HTTP redirect body
Summary
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.
Details
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…”
PoC
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 redirectTo(url, request)
site = server.Site(Simple())
reactor.listenTCP(9009, site)
reactor.run()
Once running, navigate to the following URL: http://127.0.0.1:9009?url=ws://example.com/"><script>alert(document.location)</script>, and verify that the “alert” dialog was displayed.
Note: Due to the different ways browsers validate the redirect Location header, this attack is possible only in Firefox. All other tested browsers will display an error message to the user and will not render the HTML body.
Impact
If successfully exploited, the issue will allow malicious JavaScript to run in the context of the victim’s session. This will in turn lead to unauthorized access/modification to victim’s account and information associated with it, or allow for unauthorized operations to be performed within the context of the victim’s session.
Summary
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.
Details
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…”
PoC
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 redirectTo(url, request)
site = server.Site(Simple()) reactor.listenTCP(9009, site) reactor.run()
Once running, navigate to the following URL: http://127.0.0.1:9009?url=ws://example.com/"><script>alert(document.location)</script>, and verify that the “alert” dialog was displayed.
Note: Due to the different ways browsers validate the redirect Location header, this attack is possible only in Firefox. All other tested browsers will display an error message to the user and will not render the HTML body.
Impact
If successfully exploited, the issue will allow malicious JavaScript to run in the context of the victim’s session. This will in turn lead to unauthorized access/modification to victim’s account and information associated with it, or allow for unauthorized operations to be performed within the context of the victim’s session.
References
- GHSA-cf56-g6w6-pqq2
- twisted/twisted@046a164
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Red Hat Security Advisory 2024-7312-03 - An update is now available for Red Hat Ansible Automation Platform 2.4. Issues addressed include cross site scripting and html injection vulnerabilities.
Ubuntu Security Notice 6988-1 - It was discovered that Twisted incorrectly handled response order when processing multiple HTTP requests. A remote attacker could possibly use this issue to delay and manipulate responses. This issue only affected Ubuntu 24.04 LTS. It was discovered that Twisted did not properly sanitize certain input. An attacker could use this vulnerability to possibly execute an HTML injection leading to a cross-site scripting attack.