CVE-2025-58189 is a vulnerability identified in the Go programming language's standard library, specifically within the crypto/tls package used for implementing TLS protocols. The issue arises during the ALPN (Application-Layer Protocol Negotiation) handshake phase, where if the handshake fails, the error message includes the ALPN protocols sent by the client. These protocols are attacker-controlled inputs that are logged without proper escaping or neutralization, leading to CWE-117: Improper Output Neutralization for Logs. This flaw allows an attacker to inject malicious content into log files, potentially enabling log forging or injection attacks. Such attacks can confuse log analysis, hide malicious activity, or trigger false alarms. The vulnerability affects all versions up to and including Go 1.25.0. The CVSS v3.1 score is 5.3 (medium severity), reflecting that the vulnerability is remotely exploitable without authentication or user interaction but only impacts confidentiality slightly and does not affect integrity or availability. No public exploits have been reported yet. The root cause is insufficient sanitization of attacker-controlled data before logging, a common issue in software that handles external inputs. Since crypto/tls is widely used in Go applications for secure communications, this vulnerability has a broad potential impact wherever Go is used for TLS connections.

For European organizations, the primary impact of this vulnerability lies in the potential compromise of log integrity. Attackers could inject misleading or malicious entries into logs, which may hinder incident response, forensic investigations, and security monitoring. This could delay detection of actual attacks or cause misattribution of events. While the vulnerability does not allow direct compromise of data confidentiality, integrity, or availability of systems, the indirect effects on security operations could be significant, especially in highly regulated sectors like finance, healthcare, and critical infrastructure. Organizations relying on Go-based services for TLS communications, including web servers, APIs, and microservices, are at risk. The vulnerability could be exploited remotely without credentials, increasing the attack surface. However, since no known exploits exist yet, the immediate risk is moderate but warrants proactive mitigation. The impact is more pronounced in environments with extensive logging and automated log analysis pipelines, common in European enterprises adhering to strict compliance and auditing standards.

To mitigate CVE-2025-58189, organizations should prioritize updating the Go runtime and crypto/tls package to a patched version once it becomes available from the Go project. Until an official patch is released, developers should implement manual sanitization of ALPN protocol strings before logging, ensuring that any control characters or escape sequences are neutralized to prevent log injection. Additionally, security teams should enhance log monitoring to detect anomalous or suspicious entries that could indicate exploitation attempts. Employing centralized logging solutions with integrity verification and alerting on unusual patterns can reduce the risk of undetected log tampering. Reviewing and hardening logging configurations to avoid excessive trust in raw log data is recommended. Finally, organizations should conduct code audits of custom Go applications using crypto/tls to identify and remediate any unsafe logging practices related to ALPN or other client-supplied inputs.