CVE-2026-73253: CWE-295: Improper Certificate Validation in cesanta mongoose
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.
AI Analysis
Technical Summary
CVE-2026-73253 is a critical improper certificate validation vulnerability (CWE-295) in the cesanta mongoose embedded web server and network library. Before version 7.22, the built-in TLS stack's hostname verification functions mg_tls_verify_cert_san() and mg_tls_verify_cert_cn() use mg_match() which allows wildcard certificates such as *.example.com to match unintended deeper subdomains like foo.bar.example.com. This hostname verification bypass enables an on-path attacker possessing a wildcard certificate for a parent domain to impersonate deeper subdomains to the client, potentially intercepting and modifying TLS traffic. The vulnerability is resolved in mongoose version 7.22.
Potential Impact
An attacker with a wildcard certificate for a parent domain can impersonate deeper subdomains to clients using the vulnerable mongoose TLS stack, enabling interception and modification of TLS traffic. This compromises the confidentiality and integrity of communications relying on mongoose's TLS verification prior to version 7.22.
Mitigation Recommendations
This vulnerability is fixed in mongoose version 7.22. Users should upgrade to version 7.22 or later to remediate this issue. No official patch or temporary fix is documented beyond upgrading. Since this is not a cloud service, remediation depends on applying the fixed version.
CVE-2026-73253: CWE-295: Improper Certificate Validation in cesanta mongoose
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.
CVSS v4.0
Score 9.1critical
Affected software
Run on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-73253 is a critical improper certificate validation vulnerability (CWE-295) in the cesanta mongoose embedded web server and network library. Before version 7.22, the built-in TLS stack's hostname verification functions mg_tls_verify_cert_san() and mg_tls_verify_cert_cn() use mg_match() which allows wildcard certificates such as *.example.com to match unintended deeper subdomains like foo.bar.example.com. This hostname verification bypass enables an on-path attacker possessing a wildcard certificate for a parent domain to impersonate deeper subdomains to the client, potentially intercepting and modifying TLS traffic. The vulnerability is resolved in mongoose version 7.22.
Potential Impact
An attacker with a wildcard certificate for a parent domain can impersonate deeper subdomains to clients using the vulnerable mongoose TLS stack, enabling interception and modification of TLS traffic. This compromises the confidentiality and integrity of communications relying on mongoose's TLS verification prior to version 7.22.
Mitigation Recommendations
This vulnerability is fixed in mongoose version 7.22. Users should upgrade to version 7.22 or later to remediate this issue. No official patch or temporary fix is documented beyond upgrading. Since this is not a cloud service, remediation depends on applying the fixed version.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-08-11T17:18:01.598Z
- Cvss Version
- 4.0
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a873eeeacd9273b49f2b5e0
Added to database: 08/20/2026, 17:52:46 UTC
Last enriched: 08/20/2026, 18:07:23 UTC
Last updated: 08/20/2026, 23:34:14 UTC
Views: 10
Community Reviews
0 reviewsCrowdsource mitigation strategies, share intel context, and vote on the most helpful responses. Sign in to add your voice and help keep defenders ahead.
Want to contribute mitigation steps or threat intel context? Sign in or create an account to join the community discussion.
Actions
Updates to AI analysis require Pro Console access. Upgrade inside Console → Billing.
Need more coverage?
Upgrade to Pro Console for AI refresh and higher limits.
For incident response and remediation, OffSeq services can help resolve threats faster.
Latest Threats
Check if your credentials are on the dark web
Instant breach scanning across billions of leaked records. Free tier available.