CVE-2026-11404: Cesanta Mongoose

High severity, CVSS 7.5. EPSS: 0.6% chance of exploitation in the next 30 days.

Cesanta Mongoose before 7.22 contains an out-of-bounds read in the built-in TLS server function mg_tls_server_recv_hello(), which uses an attacker-controlled session_id_len byte from a TLS ClientHello as a buffer index without validating it against the length of received data. A remote, unauthenticated attacker can send a single crafted ClientHello with an oversized session id length to read past the receive buffer, crashing any HTTPS, MQTTS, or WSS service built on MG_TLS_BUILTIN.

Affected products

• Cesanta Mongoose: before 7.22 (fixed in 7.22)

Published 2026-07-09. Last modified 2026-08-29.