CVE-2026-73257: Cesanta Mongoose

Critical severity, CVSS 9.1. EPSS: 0.7% chance of exploitation in the next 30 days.

Mongoose is an embedded web server and network library. Priro to version 7.22, a remote unauthenticated attacker can send an HTTP request containing both Content-Length and Transfer-Encoding: chunked. The cl_count and te_count checks in the mg_http_parse() and http_cb() paths in src/http.c accept both headers and prioritize chunked encoding, while a Content-Length-preferring reverse proxy can use a different request boundary. This CL.TE desynchronization can inject requests that access or modify resources in another user context. 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.