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.

A vulnerability in Mongoose, an embedded web server and network library, allows remote unauthenticated attackers to perform HTTP request smuggling against HTTP/1.0 reverse-proxy deployments. The flaw exists in the http_cb() function in src/http.c, where hm.proto.len is tested with an impossible greater-than-eight condition, causing is_http_1_0 to never be set. This logic error allows Mongoose to process chunked Transfer-Encoding that an HTTP/1.0 proxy would normally ignore. By sending a crafted request with conflicting framing, an attacker can exploit this discrepancy to smuggle requests. The impact includes unauthorized access and unauthorized state changes on the affected system. The vulnerability affects all versions of Mongoose prior to 7.22. A fix has been released in version 7.22 along with an associated GitHub commit and security advisory.