Cesanta Mongoose up to 7.21 src/http.c http_cb request smuggling

Summaryinfo

A vulnerability described as problematic has been identified in Cesanta Mongoose up to 7.21. This issue affects the function http_cb of the file src/http.c. The manipulation results in request smuggling. This vulnerability is cataloged as CVE-2026-73256. The attack may be launched remotely. There is no exploit available.

Detailsinfo

A vulnerability classified as problematic has been found in Cesanta Mongoose up to 7.21. Affected is the function http_cb of the file src/http.c. The manipulation with an unknown input leads to a request smuggling vulnerability. CWE is classifying the issue as CWE-444. The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination. This is going to have an impact on integrity. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability is traded as CVE-2026-73256 since 08/11/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. There are known technical details, but no exploit is available.

Upgrading to version 7.22 eliminates this vulnerability.

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Productinfo

Vendor

• Cesanta

Name

• Mongoose

Version

• 7.0
• 7.1
• 7.2
• 7.3
• 7.4
• 7.5
• 7.6
• 7.7
• 7.8
• 7.9
• 7.10
• 7.11
• 7.12
• 7.13
• 7.14
• 7.15
• 7.16
• 7.17
• 7.18
• 7.19
• 7.20
• 7.21

License

• open-source

Website

• Product: https://github.com/cesanta/mongoose/

CPE 2.3info

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CPE 2.2info

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