CVE-2026-73257

CRITICAL 9.1

Mongoose: Content-Length + Transfer-Encoding coexistence enables request smuggling

CVSS Score

9.1

EPSS Score

0.0%

EPSS Percentile

0th

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.

CWE	CWE-444
Vendor	cesanta
Product	mongoose
Published	Aug 20, 2026
Last Updated	Aug 20, 2026

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CVSS v3 Breakdown

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

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

None

Affected Versions

cesanta / mongoose

< 7.22

References

NVD ↗ CVE.org ↗ EPSS Data ↗

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