CVE-2026-6860: Vert.x has a DoS via unbounded server-side SNI SslContext cache growth

Potential unbounded server-side SNI SslContext cache growth in Vert.x TLS handling, with possible resource-exhaustion / DoS impact.

On affected versions, matching server-side SNI names are cached via computeIfAbsent(serverName, ...) in a serverName-keyed SslContext cache, and I could not find any bound, TTL, or eviction for that cache.

The implementation differs slightly by branch, but the same sink appears to be present in released versions 4.3.4 through 5.0.8:

• 4.3.x: SSLHelper
• 4.4.x / 4.5.x: SslChannelProvider
• 5.0.x and current master: SslContextProvider

It appears that when server-side SNI is enabled, and wildcard or otherwise broad hostname mappings are used, an unauthenticated client can send many distinct matching SNI names and cause the server to retain increasing numbers of SslContext entries over time, leading to increasing memory consumption and possible DoS conditions.

A check was performed on the related TCP SNI path across affected versions, the QUIC SNI path on 5.x, and the wildcard hostname resolution helpers used during certificate selection.