Web Cache Poisoning Affecting bottle package, versions [0,0.12.19)



    Attack Complexity High
    User Interaction Required
    Availability High

    Threat Intelligence

    Exploit Maturity Proof of concept
    EPSS 0.37% (69th percentile)
Expand this section
6.8 medium
Expand this section
6.8 medium

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  • Snyk ID SNYK-PYTHON-BOTTLE-1017108
  • published 18 Jan 2021
  • disclosed 13 Oct 2020
  • credit Snyk Security Team

How to fix?

Upgrade bottle to version 0.12.19 or higher.


Affected versions of this package are vulnerable to Web Cache Poisoning by using a vector called parameter cloaking. When the attacker can separate query parameters using a semicolon (;), they can cause a difference in the interpretation of the request between the proxy (running with default configuration) and the server. This can result in malicious requests being cached as completely safe ones, as the proxy would usually not see the semicolon as a separator, and therefore would not include it in a cache key of an unkeyed parameter.


GET /?q=legitimate&utm_content=1;q=malicious HTTP/1.1

Host: example.com

Upgrade-Insecure-Requests: 1

User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/85.0.4183.83 Safari/537.36

Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,imag e/webp,image/apng,/;q=0.8,application/signed-exchange;v=b3;q=0.9 Accept-Encoding: gzip, deflate

Accept-Language: en-US,en;q=0.9 Connection: close

The server sees 3 parameters here: q, utm_content and then q again. On the other hand, the proxy considers this full string: 1;q=malicious as the value of utm_content, which is why the cache key would only contain somesite.com/?q=legitimate.