---
id: CVE-2026-73261
title: Mongoose is an embedded web server and network library
summary: >-
  Mongoose is an embedded web server and network library. Prior to 7.23, the
  built-in TCP/IP stack enabled by MG_ENABLE_TCPIP in src/net_builtin.c does not
  reject a TCP option whose declared opts[1] length exceeds the remaining option
  byte…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-20
  - CWE-125
published: '2026-10-14'
updated: '2026-10-14'
sourceUpdated: '2026-10-14T19:17:19.990'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-73261'
references:
  - url: >-
      https://github.com/cesanta/mongoose/commit/cc7c6d2d18c28fcc6d085633dddd88402946140a
    label: security-advisories@github.com
  - url: 'https://github.com/cesanta/mongoose/releases/tag/7.23'
    label: security-advisories@github.com
  - url: >-
      https://github.com/cesanta/mongoose/security/advisories/GHSA-3fmr-92g4-wchx
    label: security-advisories@github.com
tags:
  - nvd
ingestedAt: '2026-10-14T19:49:57.615Z'
---

## Overview

Mongoose is an embedded web server and network library. Prior to 7.23, the built-in TCP/IP stack enabled by MG_ENABLE_TCPIP in src/net_builtin.c does not reject a TCP option whose declared opts[1] length exceeds the remaining option bytes. In handle_opt(), a NOP followed by a truncated MSS option causes opts[3] to be read outside the declared options area and used as the low byte of dmss. An unauthenticated remote peer can corrupt the per-connection MSS value so later mg_send() calls transmit truncated or zero-length application payloads while the TCP connection otherwise appears healthy. This issue is fixed in version 7.23.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.