Vulnerability in Cesanta Mongoose
CVE-2026-73253
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.
Vulnerability class: Improper Certificate Validation
Published · last modified .
CVSS v3 metric
CVSS v3 base score 9.1 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N.
EPSS exploit prediction
EPSS: 0.003 (25.6th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 26th percentile — 25.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.003 · change: +0.001
Affected products
- Cesanta Mongoose — versions < 7.22
Weakness classification (CWE)
References
- github.com/cesanta/mongoose/security/advisories/GHSA-jp6g-796f-39vp (Exploit, Vendor Advisory)
- github.com/cesanta/mongoose/pull/3611 (Patch, Issue Tracking)
- github.com/cesanta/mongoose/commit/a9df523f76f43a38bd53b4232b9cfd4c16869e71 (Patch)
- github.com/cesanta/mongoose/releases/tag/7.22 (Release Notes)
Frequently asked questions
- What is CVE-2026-73253?
- CVE-2026-73253 is a critical-severity vulnerability in Cesanta Mongoose, classified under Improper Certificate Validation. CVSS score: 9.1/10. Published 2026-08-20.
- How severe is CVE-2026-73253?
- Critical severity. CVSS v3 base score is 9.1 out of 10.