CVE-2025-22870 is a medium-severity vulnerability identified in the golang.org/x/net/http/httpproxy package, which is part of the Go programming language's extended networking libraries. The vulnerability arises from improper handling of IPv6 zone identifiers within the proxy host matching logic. Specifically, when the NO_PROXY environment variable is configured with patterns such as "*.example.com", the matching algorithm incorrectly interprets an IPv6 address containing a zone ID (e.g., "[::1%25.example.com]:80") as matching the NO_PROXY pattern. This misinterpretation stems from treating the zone ID component as a hostname segment, causing the system to bypass proxying for requests that should otherwise be proxied. The root cause is classified under CWE-115, which involves improper input validation or canonicalization leading to security issues. The vulnerability has a CVSS v3.1 base score of 4.4, indicating a medium severity level, with the vector showing that exploitation requires local access (AV:L), low attack complexity (AC:L), low privileges (PR:L), no user interaction (UI:N), unchanged scope (S:U), limited confidentiality impact (C:L), no integrity impact (I:N), and low availability impact (A:L). No known exploits are currently reported in the wild, and no patches are linked yet. The flaw could lead to unintended proxy bypass, potentially exposing internal network resources or sensitive data to direct access or interception, depending on the network configuration and proxy usage patterns. This vulnerability affects all versions of the httpproxy package as indicated, and it is relevant for applications and services written in Go that rely on this package for proxy configuration and HTTP request routing.

For European organizations, the impact of CVE-2025-22870 depends largely on their use of Go-based applications that utilize the golang.org/x/net/http/httpproxy package for proxy configuration. Many enterprises and cloud services in Europe employ Go for backend services, microservices, and networking tools. If these applications rely on NO_PROXY environment variables to control proxy bypass rules, this vulnerability could allow certain IPv6 requests to circumvent proxy controls unintentionally. This may lead to direct exposure of internal services or data flows that were intended to be routed through security proxies, potentially increasing the risk of data leakage, unauthorized access, or network reconnaissance by attackers with local or limited access. Given the medium severity and the requirement for local or low-privilege access, the threat is more significant in environments where users or processes have some level of access to the host or network segment. Organizations with strict proxy policies for compliance or data protection (e.g., GDPR) could face increased risk of non-compliance or data exposure. Additionally, environments heavily using IPv6 addressing and zone identifiers are more susceptible, which is increasingly common in modern European networks. The vulnerability does not directly allow remote exploitation without local access, limiting its impact to scenarios involving insider threats or compromised local accounts.

To mitigate CVE-2025-22870, European organizations should: 1) Audit all Go applications and services that utilize the golang.org/x/net/http/httpproxy package, especially those that rely on NO_PROXY environment variables for proxy bypass rules. 2) Review and sanitize NO_PROXY patterns to avoid ambiguous or overly broad wildcard entries that could be exploited via IPv6 zone ID manipulation. 3) Implement strict network segmentation and access controls to limit local or low-privilege user access to systems running vulnerable Go applications. 4) Monitor network traffic for unexpected direct connections that should be proxied, particularly involving IPv6 addresses with zone identifiers. 5) Stay updated with Go project releases and apply patches promptly once available for this vulnerability. 6) Consider deploying additional proxy validation or filtering layers that do not solely rely on the vulnerable matching logic. 7) Educate developers and system administrators about the nuances of IPv6 zone IDs and their impact on proxy configurations to prevent misconfigurations. These steps go beyond generic advice by focusing on the specific nature of the vulnerability and the operational context of proxy usage in Go applications.