TLS Traffic Interception Vulnerability in Mongoose Web Server
CVE-2026-73253

9.1CRITICAL

Key Information:

Vendor

Cesanta

Status
Mongoose
Vendor
CVE Published:
20 August 2026

What is CVE-2026-73253?

An on-path network attacker with a wildcard certificate for a parent domain can impersonate subdomains using the Mongoose web server's built-in TLS stack. This vulnerability arises because the verification functions, mg_tls_verify_cert_san() and mg_tls_verify_cert_cn(), do not properly enforce DNS label boundaries when matching wildcard certificates, allowing patterns like *.example.com to match deeper subdomains such as foo.bar.example.com. This flaw enables the potential interception and modification of TLS traffic, posing a significant security risk until corrected in version 7.22.

Affected Version(s)

mongoose < 7.22

References

https://github.com/cesanta/mongoose/security/advisories/G...
x_refsource_CONFIRM
https://github.com/cesanta/mongoose/pull/3611
x_refsource_MISC
https://github.com/cesanta/mongoose/commit/a9df523f76f43a...
x_refsource_MISC

CVSS V4

Score:
9.1
Severity:
CRITICAL
Confidentiality:
High
Integrity:
High
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
Physical
Privileges Required:
Undefined
User Interaction:
None

Timeline

  • Vulnerability published

  • Vulnerability Reserved

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