CVE-2021-23336

Python versions 0 to 3.9.2 vulnerable to Web Cache Poisoning via urllib.parse

• CVSS 5.9
• CWE-444 Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
• Input Validation and Sanitization
• Remote

The python/cpython package versions from 0 and before 3.6.13, from 3.7.0 and before 3.7.10, from 3.8.0 and before 3.8.8, from 3.9.0 and before 3.9.2 are susceptible to Web Cache Poisoning via urllib.parse.parse_qsl and urllib.parse.parse_qs 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 the 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.

CVE

CVE-2021-23336

CWE

CWE-444 Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

CVSS base score

5.9

Published

2021-02-15

OWASP

A06 Vulnerable and Outdated Components

Orthogonal defect classification

Function

Code defect classification

Incorrect Functionality

Category

Input Validation and Sanitization

Subcategory

Insecure Parsing or Deserialization

Accessibility scope

Remote

Impact

Denial of Service (DoS)

Fixed by upgrading

Yes

Solution

Upgrade to Python/Cpython version 3.9.2 or later.

import urllib.parse

def parse_qs(query_string):
    return urllib.parse.parse_qs(query_string)

if __name__ == "__main__":
    query_string = "param1=value1;param2=value2"
    parsed_params = parse_qs(query_string)
    print("Parsed parameters:", parsed_params)

import urllib.parse

def parse_qs(query_string):
    sanitized_query_string = query_string.replace(';', '&')
    return urllib.parse.parse_qs(sanitized_query_string)

if __name__ == "__main__":
    query_string = "param1=value1;param2=value2"
    parsed_params = parse_qs(query_string)
    print("Parsed parameters:", parsed_params)

@misc{vaitp:cve202123336,
  title        = {{Python versions 0 to 3.9.2 vulnerable to Web Cache Poisoning via urllib.parse}},
  author       = {Bogaerts, Fr\'ed\'eric and Ivaki, Naghmeh and Fonseca, Jos\'e},
  year         = {2021},
  note         = {VAITP Python Vulnerability Dataset, entry CVE-2021-23336},
  howpublished = {\url{https://netpack.pt/vaitp/vulnerability/CVE-2021-23336/}}
}