Improper Certificate Validation in Mongoose - CVE-2026-73251
Published: August 12, 2026
Vulnerability identifier: #VU142179
CSH Severity: Medium
CVSS v4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-73251
CWE-ID: CWE-295
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to bypass TLS server authentication and perform a man-in-the-middle attack.
The vulnerability exists due to improper certificate validation in mg_tls_recv_cert() in src/tls_builtin.c when verifying a server certificate chain against a multi-certificate PEM CA bundle. A remote attacker can present a forged certificate with a matching hostname and an issuer common name matching a root in the bundle to bypass TLS server authentication and perform a man-in-the-middle attack.
Only built-in-TLS client configurations using a CA bundle containing more than one certificate are affected.
Affected software
Mongoose
How to mitigate CVE-2026-73251
Install security update from vendor's website.
Mongoose - update to 7.23