Vulnerability · Published Aug 20, 2026 · Assigned by GitHub_M
CVE-2026-73251Mongoose Built-in TLS: CA-bundle certificate chain accepted without any signature verification
Critical 9.3
In plain English
A critical-severity improper certificate validation in mongoose from cesanta. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 9% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
Mongoose is an embedded web server and network library. Prior to 7.23, a network attacker can impersonate a TLS server to a Mongoose client configured with a multi-certificate CA bundle. In src/tls_builtin.c, the mg_tls_init() function stores the bundle in tls->ca_bundle_der while tls->ca_der.len remains zero, and mg_tls_recv_cert() uses tls_bundle_find() to accept a Common Name match without calling mg_tls_verify_cert_signature(). A forged self-signed certificate can therefore satisfy hostname and CertificateVerify checks and enable interception, credential disclosure, traffic modification, and malicious responses. This issue is fixed in version 7.23.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:14 | mongoose | 7.23+ds-1 | DEBIAN-CVE-2026-73251 |
| Ubuntu:26.10 | mongoose | no fix listed | UBUNTU-CVE-2026-73251 |
Affected products (as reported)
Weakness: CWE-295 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
References
- https://github.com/cesanta/mongoose/security/advisories/GHSA-qj6j-2692-v2r8 x_refsource_CONFIRM
- https://github.com/cesanta/mongoose/commit/2988bc9df3a5efc9539471cb7455975fa25df483 x_refsource_MISC
- https://github.com/cesanta/mongoose/releases/tag/7.23 x_refsource_MISC