# CVE-2026-73256

## Summary

- **CVE ID:** CVE-2026-73256
- **Severity:** CRITICAL
- **CVSS Score:** 9.1 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N)
- **CWE:** CWE-444
- **Published:** Aug 20, 2026
- **Last Modified:** Aug 21, 2026

## 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.

## Affected Products

- cesanta — mongoose (< 7.22)

## References

- [CNA](https://github.com/cesanta/mongoose/security/advisories/GHSA-mgp5-rjrv-h5j3)
- [CNA](https://github.com/cesanta/mongoose/pull/3611)
- [CNA](https://github.com/cesanta/mongoose/commit/a9df523f76f43a38bd53b4232b9cfd4c16869e71)
- [CNA](https://github.com/cesanta/mongoose/releases/tag/7.22)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.40%
- **EPSS Percentile:** 33.0

---
_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._