Cesanta Mongoose up to 7.22 TCP IP Stack src/net_builtin.c handle_opt input validation

Summaryinfo

A vulnerability identified as critical has been detected in Cesanta Mongoose up to 7.22. This issue affects the function handle_opt of the file src/net_builtin.c of the component TCP IP Stack. Performing a manipulation results in input validation. This vulnerability was named CVE-2026-73261. The attack may be initiated remotely. There is no available exploit. You should upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as critical, was found in Cesanta Mongoose up to 7.22. This affects the function handle_opt of the file src/net_builtin.c of the component TCP IP Stack. The manipulation with an unknown input leads to a input validation vulnerability. CWE is classifying the issue as CWE-20. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. This is going to have an impact on integrity, and availability. The summary by CVE is:

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.

It is possible to read the advisory at github.com. This vulnerability is uniquely identified as CVE-2026-73261 since 08/11/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. Technical details of the vulnerability are known, but there is no available exploit.

Upgrading to version 7.23 eliminates this vulnerability.

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Productinfo

Vendor

• Cesanta

Name

• Mongoose

Version

• 7.0
• 7.1
• 7.2
• 7.3
• 7.4
• 7.5
• 7.6
• 7.7
• 7.8
• 7.9
• 7.10
• 7.11
• 7.12
• 7.13
• 7.14
• 7.15
• 7.16
• 7.17
• 7.18
• 7.19
• 7.20
• 7.21
• 7.22

License

• open-source

Website

• Product: https://github.com/cesanta/mongoose/

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