CVE-2026-26999: Traefik: tcp router clears read deadlines before tls forwarding, enabling stalled handshakes (Slowloris DOS)

There is a potential vulnerability in Traefik managing TLS handshake on TCP routers.

When Traefik processes a TLS connection on a TCP router, the read deadline used to bound protocol sniffing is cleared before the TLS handshake is completed. When a TLS handshake read error occurs, the code attempts a second handshake with different connection parameters, silently ignoring the initial error. A remote unauthenticated client can exploit this by sending an incomplete TLS record and stopping further data transmission, causing the TLS handshake to stall indefinitely and holding connections open.

By opening many such stalled connections in parallel, an attacker can exhaust file descriptors and goroutines, degrading availability of all services on the affected entrypoint.

Each stalled connection occupies file descriptors and goroutines (and may consume additional memory depending on buffering). By opening many such connections in parallel, an attacker can cause resource exhaustion and degrade availability.