CVE-2025-61730 is a vulnerability identified in the Go standard library's crypto/tls package, specifically affecting the TLS 1.3 handshake process. TLS 1.3 handshake involves multiple messages exchanged between client and server to establish secure communication. This vulnerability occurs when multiple handshake messages are sent in records that span encryption level boundaries—for example, when the Client Hello and Encrypted Extensions messages are transmitted in a way that the subsequent messages are processed before the encryption level has actually changed. This premature processing can lead to improper verification of the source of communication channels, classified under CWE-940 (Improper Verification of Source of a Communication Channel). The flaw allows a network-local attacker, who can inject messages during the handshake, to cause minor information disclosure. This could include leaking handshake-related data that should remain confidential during the transition between encryption levels. The affected versions include Go standard library versions from 0 up to 1.25.0. No CVSS score has been assigned yet, and no known exploits have been reported in the wild. The vulnerability does not require authentication but does require the attacker to be on the same network segment or have the ability to inject packets into the handshake process. The root cause is the incorrect handling of message boundaries and encryption level transitions during the handshake, which leads to processing messages out of order or prematurely, thus exposing some information that should be protected. This vulnerability could impact any application or service relying on the Go crypto/tls package for TLS 1.3 communications, including web servers, APIs, and microservices.

For European organizations, this vulnerability poses a confidentiality risk during TLS 1.3 handshakes in Go-based applications. Although the information disclosure is described as minor, it could potentially leak sensitive handshake data that might aid attackers in further reconnaissance or cryptographic attacks. Organizations in sectors such as finance, healthcare, and critical infrastructure that rely heavily on Go for secure communications could be at risk. The requirement for network-local attacker capability limits the threat to environments where attackers can intercept or inject traffic, such as unsecured Wi-Fi networks or compromised internal networks. However, given the widespread use of Go in cloud-native applications and microservices architectures, the vulnerability could affect a broad range of services. The lack of known exploits reduces immediate risk but does not eliminate the potential for future exploitation. The impact on integrity and availability is minimal, but confidentiality degradation could undermine trust in secure communications and compliance with data protection regulations like GDPR.

1. Monitor official Go project channels for the release of patches addressing CVE-2025-61730 and prioritize upgrading to the fixed versions beyond 1.25.0 as soon as they become available. 2. In the interim, restrict network access to critical Go-based services using network segmentation, firewall rules, and zero-trust principles to limit the ability of attackers to perform network injection attacks. 3. Employ TLS inspection and anomaly detection tools that can identify unusual handshake message patterns indicative of injection attempts. 4. Review and harden internal network security, especially in environments where Go applications operate, to prevent local attackers from gaining network access. 5. Conduct thorough code audits and testing of custom Go TLS implementations or wrappers to ensure they do not exacerbate the vulnerability. 6. Educate developers and system administrators about the risks of improper TLS handshake handling and encourage best practices for secure communication. 7. Consider deploying additional endpoint security controls to detect and prevent man-in-the-middle or injection attacks at the network level.