The Go TLS 1.3 implementation incorrectly processes a batch of key update messages sent in a single record after the handshake. When such duplicate key updates are received, the connection can deadlock, leading to uncontrolled consumption of system resources and a denial of service. This vulnerability can be triggered by an attacker sending a crafted TLS session that includes multiple key update records.

The vulnerability affects the Go standard library package crypto/tls and therefore any Go application that enables TLS 1.3 handling through this library. The issue is present in all versions of Go that use the affected TLS implementation, regardless of vendor or product beyond the Go runtime. No specific product naming beyond Go’s standard library is required for the impact assessment.

With a CVSS score of 7.5 the vulnerability is classified as high severity, while the EPSS score of less than 1% indicates a low likelihood of being actively exploited at the present time. The attacker only needs to supply a malformed TLS session and does not require any special privileges or prior access. The vulnerability is remote and does not require authentication to impact the system. Although it is not listed in the CISA Known Exploited Vulnerabilities catalog, it poses a significant risk if an undetected attacker can trigger the deadlock on a high‑traffic service. The recommended mitigations focus on applying the vendor patch or disabling TLS 1.3 until a fix is available.