CVE-2026-73261: CWE-20: Improper Input Validation in cesanta mongoose
Description
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.
CVSS v3.1
Score 7.5high
Affected software
cesanta
mongoose
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-08-11T17:18:01.598Z
- Cvss Version
- 3.1
- State
- PUBLISHED
Threat ID: 6acfceae2cdf04f656a1f7e5
Added to database: 10/14/2026, 18:49:18 UTC
Last updated: 10/14/2026, 18:49:18 UTC
Views: 1
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