CVE-2026-73253: Cesanta Mongoose

Critical severity, CVSS 9.1. EPSS: 0.3% chance of exploitation in the next 30 days.

Mongoose is an embedded web server and network library. Prior to version 7.22, an on-path network attacker with a wildcard certificate for a parent domain can impersonate deeper subdomains to a client using the built-in TLS stack. The mg_tls_verify_cert_san() and mg_tls_verify_cert_cn() functions in src/tls_builtin.c call mg_match(), whose wildcard can cross DNS label boundaries, so a pattern such as *.example.com can match foo.bar.example.com. The resulting hostname verification bypass permits interception and modification of TLS traffic. This issue is fixed in version 7.22.

Affected products

• Cesanta Mongoose: before 7.22 (fixed in 7.22)

Published 2026-08-20. Last modified 2026-09-29.