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-2026-73256

CVE-2026-73256CRITICAL

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

  AV  AC  PR  UI  S  C  I  A   CVSS    EPSS   %ile   KEV
   N   L   N   N  U  H  H  N    9.1   .0044   35.9     —

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-2026-73256 (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. 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.

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-2026-73256 (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-mgp5-rjrv-h5j3 [Exploit, Vendor Advisory]

Authoritative record: CVE-2026-73256 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-2026-73256 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.