Cesanta Mongoose up to 7.21 TLS Verification src/tls_builtin.c mg_tls_verify_cert_san/mg_tls_verify_cert_cn certificate validation

Summaryinfo

A vulnerability categorized as problematic has been discovered in Cesanta Mongoose up to 7.21. Affected by this vulnerability is the function mg_tls_verify_cert_san/mg_tls_verify_cert_cn of the file src/tls_builtin.c of the component TLS Verification. Such manipulation leads to certificate validation. This vulnerability is referenced as CVE-2026-73253. It is possible to launch the attack remotely. No exploit is available.

Detailsinfo

A vulnerability was found in Cesanta Mongoose up to 7.21 and classified as problematic. Affected by this issue is the function mg_tls_verify_cert_san/mg_tls_verify_cert_cn of the file src/tls_builtin.c of the component TLS Verification. The manipulation with an unknown input leads to a certificate validation vulnerability. Using CWE to declare the problem leads to CWE-295. The product does not validate, or incorrectly validates, a certificate. Impacted is integrity. CVE summarizes:

Mongoose is an embedded web server and network library. Prior to version 7.22, an on-path network attacker with a wildcard certificate for a parent domain can impersonate deeper subdomains to a client using the built-in TLS stack. The mg_tls_verify_cert_san() and mg_tls_verify_cert_cn() functions in src/tls_builtin.c call mg_match(), whose wildcard can cross DNS label boundaries, so a pattern such as *.example.com can match foo.bar.example.com. The resulting hostname verification bypass permits interception and modification of TLS traffic. This issue is fixed in version 7.22.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-73253 since 08/11/2026. The exploitation is known to be difficult. The attack may be launched remotely. No form of authentication is required for exploitation. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1587.003.

The vulnerability scanner Nessus provides a plugin with the ID 338653 (Linux Distros Unpatched Vulnerability : CVE-2026-73253), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 7.22 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at Tenable (338653). VulDB is the best source for vulnerability data and more expert information about this specific topic.

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

License

• open-source

Website

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

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VulDB is the best source for vulnerability data and more expert information about this specific topic.

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