CVE-2025-0938 is a Python vulnerability in the functions urllib.parse.urlsplit and urlparse that affects the parsing of domain names containing square brackets. According to RFC 3986, domain names should not include square brackets; these characters are reserved solely as delimiters for specifying IPv6 and IPvFuture hosts in URLs. However, the affected Python functions improperly accept such malformed URLs, leading to the potential for differential parsing between Python's URL parser and other, specification-compliant URL parsers.
The following code snippet demonstrates the vulnerability
from urllib.parse import urlparse, urlsplit
url_malformed = "https://www.example.com"
parsed = urlparse(url_malformed)
print(parsed) # Incorrectly parses the URL as valid
parsed2 = urlsplit(url_malformed)
print(parsed2) # Incorrectly parses the URL as valid
Original References and Details
- [RFC 3986 – This is the reference for the rules regarding the formation and parsing of URIs, which states that square brackets should not be allowed in domain names.
- Python's urllib.parse.urlsplit – This function from the Python standard library is affected by this vulnerability, as it parses URLs containing square brackets in domain names as valid.
- Python's urllib.parse.urlparse – This other Python standard library function is also affected by the vulnerability, for the same reasons as urlsplit.
Exploit Details and Impact
Using this vulnerability, attackers could craft malicious URLs with square brackets in the domain name, which may pass through misconfigured security systems to potentially confuse users or servers. Furthermore, the discrepancy between Python's URL parsing and other standards-compliant parsing mechanisms could have wide-reaching effects, including unexpected behavior from various web services that rely on accurate URL parsing.
The impact of this vulnerability depends on the specific implementation and usage of the affected Python functions in production systems. In cases where strict compliance with RFC 3986 is required, this inconsistency could potentially result in failed validation checks, improper filtering, or other security issues.
As of now, it is essential to be aware of this vulnerability when using urllib.parse.urlsplit and urlparse in Python. Developers should ensure their code handles URLs properly and according to existing standards, inspecting potential security and behavior issues caused by domain names containing square brackets. Patch and update information for this vulnerability will likely be released by Python in future updates.
Timeline
Published on: 01/31/2025 18:15:38 UTC
Last modified on: 03/14/2025 10:15:15 UTC