STEK Sharing is Not Caring: Bypassing TLS Authentication in Web Servers using Session Tickets

Sven Hebrok, Tim Leonhard Storm, Felix Matthias Cramer, Maximilian Radoy, Juraj Somorovsky

34th USENIX Security Symposium · Day 1

This article delves into a critical security vulnerability discovered in how modern web servers handle TLS session resumption, particularly in virtual hosting environments. Researchers from Paderborn University, Sven Hebrok, Tim Leonhard Storm, Felix Matthias Cramer, Maximilian Radoy, and Juraj Somorovsky, presented their findings on "session ticket confusion" attacks. These attacks exploit the shared use of **Session Ticket Encryption Keys (STEKs)** across multiple virtual hosts, leading to the bypass of both server and client authentication in TLS connections.

AI review

Real research, real vulns, real CVEs. The Paderborn team found a legit class of authentication bypasses in TLS session resumption that hit Apache, nginx, Caddy, LiteSpeed, and major CDNs including Cloudflare and Fastly. This is the kind of work that actually changes how servers should be configured.