ARM mbed TLS before 1.3.22, before 2.1.10, and before 2.7.0 allows remote attackers to execute arbitrary code or cause a denial of service (buffer overflow) via a crafted certificate chain that is mishandled during RSASSA-PSS signature verification within a TLS or DTLS session.
https://www.debian.org/security/2018/dsa-4147
https://www.debian.org/security/2018/dsa-4138
https://usn.ubuntu.com/4267-1/
https://tls.mbed.org/tech-updates/security-advisories/mbedtls-security-advisory-2018-01