Reference page — cumulative record through Saturday, October 3, 2026 UTC. Reference pages update as the archive grows; only dated daily editions are immutable pages of record.

CVE-2026-73257

CVE-2026-73257CRITICAL

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

  AV  AC  PR  UI  S  C  I  A   CVSS    EPSS   %ile   KEV
   N   L   N   N  U  H  H  N    9.1   .0067   50.3     —

AFFECTED
  Product   Versions  Fixed
  mongoose  < 7.22 –  —

TIMELINE
  Aug 11  Reserved by GitHub_M
  Aug 20  Published (CNA: GitHub_M)
  Sep 29  EXPLOIT PUBLISHED — CVE-2026-73257 (cesanta mongoose). Public exploit reference added.

CWE-444 · CNA: GitHub_M · CVSS v3.1 · 4 references · NVD status: Analyzed

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.

Lifecycle

Complete event history — 3 events, chronological
Date	Event	Detail
August 11, 2026	Reserved	Reserved by GitHub_M
August 20, 2026	Published	Published (CNA: GitHub_M)
September 29, 2026	EXPLOIT PUBLISHED	EXPLOIT PUBLISHED — CVE-2026-73257 (cesanta mongoose). Public exploit reference added.

Affected

Affected products and packages — 1 row
Vendor	Product / Package	Ecosystem	Version introduced	Fixed
cesanta	mongoose	—	< 7.22	—

Weaknesses

CWE-444

References (4)

https://github.com/cesanta/mongoose/commit/a9df523f76f43a38bd53b4232b9cfd4c16869e71 [Patch]
https://github.com/cesanta/mongoose/pull/3611 [Issue Tracking, Patch]
https://github.com/cesanta/mongoose/releases/tag/7.22 [Release Notes]
https://github.com/cesanta/mongoose/security/advisories/GHSA-5wfq-r6mr-wqp6 [Exploit, Vendor Advisory]

Authoritative record: CVE-2026-73257 at cve.org

Vendors: cesanta

Weaknesses: CWE-444

About this page

This is a reference page, not a dated page of record. It assembles the complete lifecycle of CVE-2026-73257 from the CVE Program record, NVD enrichment, the CISA KEV catalog, EPSS, and OSV advisories. The box score's numbers (CVSS, EPSS, KEV status) are current as of Saturday, October 3, 2026 UTC and are re-derived as the archive grows; only dated daily editions are immutable pages of record. The authoritative source for this identifier is cve.org.