CVE-2026-73253
Received Received - Intake

Mongoose TLS Hostname Verification Bypass via Wildcard Certificates

Publication date: 2026-08-20

Last updated on: 2026-08-20

Assigner: GitHub, Inc.

Description
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.

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Meta Information

Published
2026-08-20
Last Modified
2026-08-20
Generated
2026-08-20
AI Q&A
2026-08-20
EPSS Evaluated
N/A
NVD
CVE-2026-73253
EUVD
EUVD-2026-63500

Affected Vendors & Products

Showing 2 associated CPEs
Vendor Product Version / Range
mongoose mongoose 7.22
cesanta mongoose to 7.22 (exc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-295 The product does not validate, or incorrectly validates, a certificate.

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Executive Summary

This vulnerability is a TLS hostname verification bypass in the Mongoose library caused by overly permissive wildcard matching. The mg_match() function incorrectly treats wildcards as matching any character including dots, violating RFC 6125. This allows certificates like *.example.com to match hostnames such as foo.bar.example.com, enabling man-in-the-middle attacks.

Detection Guidance

To detect this vulnerability, check if your Mongoose library version is 7.21 or earlier. Run commands like 'mongoose --version' or inspect your application's dependency files for the version. If using a package manager, commands like 'npm list mongoose' or 'pip show mongoose' may help. Network monitoring tools can detect unusual TLS handshakes or certificate mismatches.

Impact Analysis

An attacker with a wildcard certificate for a parent domain could impersonate deeper subdomains, intercepting and modifying TLS traffic. This could lead to unauthorized access to sensitive data, session hijacking, or man-in-the-middle attacks on applications using vulnerable Mongoose versions.

Compliance Impact

This vulnerability undermines secure communication requirements in GDPR and HIPAA by allowing unauthorized interception of encrypted data. Non-compliance may result from failing to implement proper certificate validation, potentially violating data protection and privacy standards.

Mitigation Strategies

Upgrade Mongoose to version 7.22 or later immediately. Replace any vulnerable versions in your applications or systems. If upgrading is not possible, disable TLS hostname verification as a temporary workaround, though this reduces security. Monitor network traffic for suspicious TLS interception attempts.

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