CVE-2026-73253 Mongoose: TLS Hostname Verification Bypass via Overly Permissive Wildcard Matching
An on-path attacker can bypass TLS hostname verification in Mongoose to intercept and modify traffic using a wildcard certificate.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-73253?
CVE-2026-73253 is a critical vulnerability in Cesanta Mongoose, published on 20 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-295
Which versions are affected by CVE-2026-73253?
It affects 1 product.
Products include Cesanta Mongoose.
How do I fix CVE-2026-73253?
Upgrade to a fixed version.
Is CVE-2026-73253 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-73253 exists.
Other vulnerabilities in Cesanta Mongoose
Sources
Also known as DEBIAN-CVE-2026-73253, GHSA-jp6g-796f-39vp, JLSEC-2026-1377, UBUNTU-CVE-2026-73253.