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Vulnerability record · CVE-2026-73257 · published 20 August 2026

CVE-2026-73257: HTTP request smuggling vulnerability

Mongoose is an embedded web server and network library. Priro to version 7.22, a remote unauthenticated attacker can send an HTTP request containing both Content-Length and Transfer-Encoding: chunked. The cl_count and te_count checks in the mg_http_parse() and http_cb() paths in src/http.c accept both headers and prioritize chunked encoding, while a Content-Length-preferring reverse proxy can use a different request boundary. This CL.TE desynchronization can inject requests that access or modify resources in another user context. This issue is fixed in version 7.22.

9.1 CVSS 3.1 Critical EPSS 0.67% · top 50.0% CWE-444 · HTTP request smuggling Awaiting Analysis
9.1CVSS 3.1 base score
0.67%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
5References
9 Sep 2026Last modified by NVD

Description

Mongoose is an embedded web server and network library. Priro to version 7.22, a remote unauthenticated attacker can send an HTTP request containing both Content-Length and Transfer-Encoding: chunked. The cl_count and te_count checks in the mg_http_parse() and http_cb() paths in src/http.c accept both headers and prioritize chunked encoding, while a Content-Length-preferring reverse proxy can use a different request boundary. This CL.TE desynchronization can inject requests that access or modify resources in another user context. This issue is fixed in version 7.22.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

References

LinkTags
https://github.com/cesanta/mongoose/commit/a9df523f76f43a38bd53b4232b9cfd4c16869e71
https://github.com/cesanta/mongoose/pull/3611
https://github.com/cesanta/mongoose/releases/tag/7.22
https://github.com/cesanta/mongoose/security/advisories/GHSA-5wfq-r6mr-wqp6
https://github.com/cesanta/mongoose/security/advisories/GHSA-5wfq-r6mr-wqp6

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Source: NIST National Vulnerability Database (record CVE-2026-73257), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.