When Conn.Handshake fails during ALPN negotiation the error contains attacker controlled information (the ALPN protocols sent by the client) which is not escaped.
Exploitability
AV:NAC:LPR:NUI:NScope
S:UImpact
C:LI:NA:N5.3/CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N