by Kastro
Paper/Archive/CVE-2026-73256

CVE-2026-73256

cesanta mongoose — Mongoose: HTTP/1.0 detection off-by-one enables request smuggling via chunked TE

EPSS 0.4%CVSS 9.1
critical.is priorityof 100
35
CVSS 9.1 (CNA)9.1 / 10 × 3027.3Not in CISA KEV+300.0EPSS percentile 38.2.382 × 207.6No public exploit+100.0SSVC exploitation: none+100.0
Description · from the CVE record

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

ProductAffectedFixed inSource
mongoose< 7.22–CNA

Scores by source

GitHub_M (CNA)9.1CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
CISA ADPSSVCExploitation: none · Automatable: yes · Technical impact: total

References

refgithub.com/cesanta/mongoose/security/advisories/GHSA-mgp5-rjrv-h5j3refgithub.com/cesanta/mongoose/pull/3611refgithub.com/cesanta/mongoose/commit/a9df523f76f43a38bd53b4232b9cfd4c16869e71refgithub.com/cesanta/mongoose/releases/tag/7.22