CVE-2016-9964: CRLF Attack in bottle

Background

Bottle is a lightweight Python web framework that allows developers to build web applications. It provides a simple and intuitive API for handling HTTP requests and responses. The vulnerability identified as CVE-2016-9964 affects versions 0.12.10 and earlier of the Bottle package. This vulnerability arises from the lack of filtering of a "\r\n" sequence in the redirect() function of bottle.py. An attacker can exploit this vulnerability by making a redirect() call with a malicious payload that includes a CRLF sequence. This can lead to a CRLF attack, allowing the attacker to inject arbitrary HTTP headers or perform other malicious actions.

Vulnerability Detail

The vulnerability in bottle.py allows for a CRLF attack, which occurs when an attacker can inject CRLF sequences into an HTTP response. This can have several consequences, including HTTP response splitting, cache poisoning, cross-site scripting (XSS), session hijacking, and other attacks. In the case of bottle.py, the redirect() function is vulnerable to this attack because it does not properly filter out the "\r\n" sequence from the redirect URL. An attacker can exploit this by crafting a redirect URL that includes a CRLF sequence followed by arbitrary HTTP headers. When the redirect is performed, the malicious headers will be included in the response, potentially leading to further exploitation.

pip install --upgrade "bottle==6d7e13da0f998820800ecb3fe9ccee4189aefb54"

Workaround

If upgrading to a fixed version of Bottle is not immediately feasible, a temporary workaround can be implemented by manually filtering out the "\r\n" sequence from the redirect URL before passing it to the redirect() function. This can be done by using a regular expression or string manipulation to remove any occurrences of "\r\n" from the URL. Here's an example of how this can be done in Python:

import re

def sanitize_redirect_url(url):
    sanitized_url = re.sub(r'\r\n', '', url)
    return sanitized_url

redirect(sanitize_redirect_url('233\r\nSet-Cookie: name=salt'))

Conclusion

The CRLF vulnerability in bottle.py (CVE-2016-9964) allows for a CRLF attack, which can have serious consequences for web applications. It is crucial to upgrade to a fixed version of the Bottle package (0.12.11 or later) to mitigate this vulnerability. If immediate upgrade is not possible, implementing a workaround to filter out the "\r\n" sequence from redirect URLs can provide temporary protection. For further support and assistance in vulnerability remediation, please contact DevNack.com.

See every vulnerability recorded for bottle →

FAQ