What is CVE-2025-27809?

CVE-2025-27809 is a medium-severity vulnerability in Arm Mbed TLS, classified under Initialization of a Resource with an Insecure Default. CVSS score: 5.4/10. Published 2025-03-25.

How severe is CVE-2025-27809?

Medium severity. CVSS v3 base score is 5.4 out of 10.

RCE in Arm Mbed TLS

CVE-2025-27809

Mbed TLS before 2.28.10 and 3.x before 3.6.3, on the client side, accepts servers that have trusted certificates for arbitrary hostnames unless the TLS client application calls mbedtls_ssl_set_hostname.

Published 2025-03-25 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.002 (9.4th percentile), scored 2026-10-19.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 9th percentile — 9.4% 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: 0.002 · change: +0.000

Affected products

Weakness classification (CWE)

CWE-1188 — Initialization of a Resource with an Insecure Default

References

github.com/Mbed-TLS/mbedtls/releases (Release Notes)
mbed-tls.readthedocs.io/en/latest/security-advisories/mbedtls-security-advisory… (Third Party Advisory)
af854a3a-2127-422b-91ae-364da2661108 (Issue Tracking)
af854a3a-2127-422b-91ae-364da2661108 (Not Applicable)

Frequently asked questions

What is CVE-2025-27809?: CVE-2025-27809 is a medium-severity vulnerability in Arm Mbed TLS, classified under Initialization of a Resource with an Insecure Default. CVSS score: 5.4/10. Published 2025-03-25.
How severe is CVE-2025-27809?: Medium severity. CVSS v3 base score is 5.4 out of 10.