GHSA-26gq-p25f-99cp: frp: Unauthenticated Remote Denial of Service in the frp SSH Tunnel Gateway via Integer Overflow

An integer-overflow vulnerability in the frp server’s optional SSH Tunnel Gateway lets any unauthenticated remote attacker crash the entire frps process with a single five-byte message. When the gateway parses an SSH exec channel request in pkg/ssh/server.go, it adds a small constant to a four-byte length value taken directly from the request. Because that length is fully attacker-controlled, a value of 0xFFFFFFFF makes the addition wrap around to a tiny number, defeating the only bounds check and forcing an out-of-range slice. Go raises a panic that nothing recovers, so the whole server exits. In the default gateway mode SSH clients are not authenticated and the request is handled before any frp token is checked, so the crash is reachable pre-authentication. It carries no state and is trivially repeatable, turning one crash into a sustained outage that drops every tunnel for every user.