Malformed SHA512 ticket DoS (CVE-2016-6302)

Summary

If a server uses SHA512 for TLS session ticket HMAC it is vulnerable to a DoS attack where a malformed ticket will result in an OOB read which will ultimately crash.

The use of SHA512 in TLS session tickets is comparatively rare as it requires a custom server callback and ticket lookup mechanism.

OpenSSL 1.0.2 users should upgrade to 1.0.2i OpenSSL 1.0.1 users should upgrade to 1.0.1u

This issue was reported to OpenSSL on 19th August 2016 by Shi Lei (Gear Team, Qihoo 360 Inc.). The fix was developed by Stephen Henson of the OpenSSL development team.