CVE-2025-47912 identifies a vulnerability in the Go programming language's standard library, specifically within the net/url package's Parse function. According to RFC 3986, IPv6 addresses in URLs must be enclosed in square brackets within the host component, e.g., "http://[::1]/". IPv4 addresses and hostnames, however, must not be enclosed in square brackets. The vulnerability arises because the Parse function does not enforce this syntactic rule, permitting non-IPv6 values to appear within square brackets. This improper validation (CWE-1286) can cause the URL parser to accept malformed URLs that deviate from the standard, potentially leading to incorrect parsing outcomes. Such parsing errors can be exploited in scenarios where applications rely on the net/url package for security-critical decisions, such as access control, URL filtering, or routing. For example, an attacker might craft URLs that bypass hostname checks or cause unexpected behavior in downstream components. The vulnerability affects all Go versions from the initial release up to 1.25.0. As of the publication date, no public exploits are known, and no patches have been linked yet. The issue was reserved in May 2025 and published in October 2025. The lack of a CVSS score suggests the need for an independent severity assessment. Given the nature of the flaw, it primarily impacts confidentiality and integrity by enabling potential bypasses or injection vectors, but does not directly cause denial of service or remote code execution. Exploitation requires crafting specific URLs and may depend on application context, so user interaction or additional conditions might be necessary.

For European organizations, this vulnerability poses a moderate risk primarily to web services, APIs, and networked applications developed in Go that rely on the net/url package for URL parsing and validation. Incorrect parsing of URLs can lead to security bypasses, such as circumventing hostname-based access controls, evading input filters, or enabling injection attacks. This can compromise application integrity and confidentiality by allowing unauthorized access or manipulation of data. Organizations in sectors like finance, telecommunications, and critical infrastructure that use Go extensively for backend services could face targeted exploitation attempts once proof-of-concept exploits emerge. The lack of known exploits currently limits immediate impact, but the widespread use of Go in cloud-native and microservices architectures across Europe increases the attack surface. Additionally, improper URL validation can complicate logging and monitoring, making detection of malicious activity more difficult. The vulnerability does not directly affect availability but could indirectly impact service reliability if exploited in complex attack chains.

European organizations should proactively monitor Go releases and update the net/url package to a patched version as soon as it becomes available. In the interim, developers should implement additional validation layers to enforce RFC 3986 compliance, specifically ensuring that only IPv6 addresses appear within square brackets in URLs. Security teams should audit codebases for custom URL parsing logic that relies on net/url and consider adding strict input sanitization and validation routines. Employing Web Application Firewalls (WAFs) with rules to detect malformed URLs or suspicious bracket usage can provide a defensive layer. Logging and monitoring should be enhanced to detect anomalous URL patterns that could indicate exploitation attempts. Security training for developers on proper URL handling and awareness of this vulnerability will reduce the risk of introducing exploitable code. Finally, organizations should conduct penetration testing focusing on URL parsing and validation to identify potential attack vectors related to this flaw.