Go crypto/tls CVE-2026-56862: TLS 1.3 Handshake State Bypass Fix

Vulnerability Overview In TLS 1.3, handshake messages (such as ) are incorrectly counted as advancing the connection state, regardless of whether the handshake has completed. This allows a malicious client to force key derivation on the server by sending messages, thereby bypassing the restrictions on non-advancing records. Scope CVE Number: CVE-2026-56862 Go Version: Go 1.27 Related Project: Remediation 1. Code Changes: - The module was modified to ensure handshake messages are not counted as advancing the connection state. - Related code change link: https://go.dev/cl/804261 2. Patch Submission: - The patch has been submitted to the master branch, and cherry-pick CLs have been created for Go 1.25 and Go 1.26 versions. - Related patch links: - https://go.dev/cl/80530 (for 1.25) - https://go.dev/cl/80531 (for 1.26) 3. Version Updates: - The patch has been merged into the Go 1.27 release branch. - Related commit links: - https://go.dev/cl/806841 (commit 95ae641) - https://go.dev/cl/806941 (release-branch.go1.27) - https://go.dev/cl/806960 (release-branch.go1.26) POC Code No specific POC code or exploit code was provided in the source material. Summary This vulnerability involves incorrect handling of handshake messages in TLS 1.3, which could allow malicious clients to bypass restrictions on non-advancing records. The remediation includes code changes and patch submissions to ensure handshake messages are not counted as advancing the connection state. The patch has been merged into the Go 1.27 release branch, with cherry-pick CLs created for Go 1.25 and Go 1.26 versions.

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Go crypto/tls CVE-2026-56862: TLS 1.3 Handshake State Bypass Fix