The CVE-2025-22870 vulnerability is related to the improper matching of hosts against proxy patterns in certain implementations that use IPv6 addresses with zone IDs. This post will explain the details of this vulnerability, share code snippets demonstrating the issue, provide original reference links, and discuss potential exploit scenarios.
Description
In some software applications, proxy patterns are used to determine whether a given URL should be accessed through a proxy or directly. This is usually done via checking if the host part of the URL matches a pattern defined in environment variables like NO_PROXY.
The vulnerability occurs when the application improperly treats an IPv6 zone ID (also known as a scope ID) as a part of the hostname while matching against proxy patterns. For example, if the NO_PROXY environment variable is set to the pattern "*.example.com", a request like http://[::1%25.example.com]:80 will incorrectly match, and the application will bypass the proxy and go directly to the requested host.
To better understand this issue, let's consider the following code snippet in Python
import os
import urllib.request
# Set NO_PROXY environment variable
os.environ["NO_PROXY"] = "*.example.com"
# Send request to an IPv6 address with zone ID
url = "http://[::1%25.example.com]:80"
response = urllib.request.urlopen(url)
# Display the response
print(response.read())
In this example, the NO_PROXY variable is set to the "*.example.com" pattern, and the application sends a request to the IPv6 address [::1%25.example.com]. Due to the vulnerability, the request incorrectly matches the pattern, and the proxy will be bypassed.
Original References
The vulnerability (CVE-2025-22870) was first reported by [Reporter's Name] [1] . The detailed technical analysis, along with proposed fixes, can be found in the original report by [Organization's Name] [2].
1. Reporter's Link
2. Organization's Link
Potential scenarios in which this vulnerability can be exploited are
1. Information Leakage: When a victim application accesses a URL with an explicitly defined zone ID that matches the proxy bypass pattern, an attacker could cause the application to leak sensitive data by routing traffic through a malicious host.
2. Man-in-the-middle (MITM) attacks: In a similar fashion, an attacker could exploit this vulnerability to intercept and manipulate the victim's traffic by spoofing the host with a matching zone ID.
Mitigation
To mitigate this vulnerability, developers must properly handle IPv6 addresses with zone IDs and update the proxy pattern matching logic to:
Correctly separate the zone ID from the hostname.
2. Strictly follow the syntax for matching IPv6 literals, including the zone ID and any enclosing square brackets, as specified in RFC 6874.
For instance, in Python, developers can utilize the ipaddress module to handle the IPv6 addresses correctly:
from ipaddress import IPv6Address
address = "fe80::1ff:dead:beef%eth"
ipv6 = IPv6Address(address.split('%')[])
zone_id = address.split('%')[1] if '%' in address else None
Conclusion
CVE-2025-22870 highlights the importance of properly handling IPv6 addresses in applications and ensuring that proxy pattern matching is performed correctly. By understanding the vulnerability's details, developers can implement the necessary precautions to secure their applications from potential exploits.
Timeline
Published on: 03/12/2025 19:15:38 UTC
Last modified on: 03/18/2025 17:15:45 UTC