CVE-2026-73256 – Mongoose: HTTP/1.0 detection off-by-one enables request smuggling via chunked TE

​CVE ID :CVE-2026-73256

Published : Aug. 20, 2026, 6:16 p.m. | 28 minutes ago

Description :Mongoose is an embedded web server and network library. Prior to 7.22, a remote unauthenticated attacker can exploit an HTTP/1.0 reverse-proxy deployment by sending a request with Transfer-Encoding: chunked and conflicting framing. The http_cb() function in src/http.c tests hm.proto.len with an impossible greater-than-eight condition even though mg_http_parse() requires an eight-byte protocol string, so is_http_1_0 is never set. Mongoose consequently processes chunked encoding that an HTTP/1.0 proxy can ignore, enabling request smuggling and unauthorized access or state changes. This issue is fixed in version 7.22.

Severity: 9.1 | CRITICAL

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