TLS interception via wildcard hostname overmatch
Published Aug 20, 2026 · Updated Aug 20, 2026
Improper certificate validation in built-in TLS in Cesanta Mongoose before 7.22 allows man-in-the-middle attackers to intercept TLS traffic. The mg_tls_verify_cert_san() and mg_tls_verify_cert_cn() functions in src/tls_builtin.c pass certificate SAN and CN values to mg_match(), whose wildcard matches dots and therefore accepts parent-domain patterns across multiple DNS labels. Exploitation requires network-path position and a wildcard certificate for a parent domain, after which deeper subdomains can be impersonated to read or modify client traffic.
Summary
What happened
Improper certificate validation in built-in TLS in Cesanta Mongoose before 7.22 allows man-in-the-middle attackers to intercept TLS traffic. The mg_tls_verify_cert_san() and mg_tls_verify_cert_cn() functions in src/tls_builtin.c pass certificate SAN and CN values to mg_match(), whose wildcard matches dots and therefore accepts parent-domain patterns across multiple DNS labels. Exploitation requires network-path position and a wildcard certificate for a parent domain, after which deeper subdomains can be impersonated to read or modify client traffic.
The record
- CVE
- CVE-2026-73253
- Published
- Aug 20, 2026
- Updated
- Aug 20, 2026
- Vendor
- Cesanta
- Product
- Mongoose
- Classifications
- CWE-295, T1557
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Aug 20, 2026CVE publishedPublication date reported by the CVE source.
- Aug 20, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=< 7.22
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Public exploit references
- GHSA wildcard hostname overmatch proof of conceptproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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