ARM mbed TLS before 2.12.0, before 2.7.5, and before 2.1.14 allows local users to achieve partial plaintext recovery (for a CBC based ciphersuite) via a cache-based side-channel attack.
https://www.debian.org/security/2018/dsa-4296
https://usn.ubuntu.com/4267-1/
https://tls.mbed.org/tech-updates/security-advisories/mbedtls-security-advisory-2018-02
https://lists.debian.org/debian-lts-announce/2018/09/msg00029.html