#VU106010 Improper certificate validation in mbed TLS - CVE-2025-27809

Vulnerability identifier: #VU106010

Vulnerability risk: Medium

CVSSv4.0: 1.7 [CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N/E:U/U:Green]

CVE-ID: CVE-2025-27809

CWE-ID: CWE-295

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
mbed TLS
Universal components / Libraries / Libraries used by multiple products

Vendor: ARM

Description

The vulnerability allows a remote attacker to perform MitM attack.

The vulnerability exists within the client authentication process during certificate-based authentication. Due to insecure default behavior,  if a TLS client application does not call mbedtls_ssl_set_hostname(), the server verification step is skipped. As a result, a remote attacker can supply any valid certificate signed by a trusted CA and perform MitM attack.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

mbed TLS: 2.7.18 - 2.7.19, 2.16.9 - 2.16.12, 2.25.0 - 2.28.9, 3.0.0, 3.1.0, 3.2.0, 3.2.1, 3.3.0, 3.4.0, 3.4.1, 3.5.0 - 3.5.2, 3.6.0 - 3.6.2

---

External links
https://github.com/ARMmbed/mbedtls/releases/tag/mbedtls-2.28.10
https://github.com/ARMmbed/mbedtls/releases/tag/mbedtls-3.6.3
https://mbed-tls.readthedocs.io/en/latest/security-advisories/mbedtls-security-advisory-2025-03-1/

---

Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.